engine: geometry.face.split, a face split along a datum plane (#508 )

geometry.face.split {name, face, datum} records a face split; it is applied after the merges whenever the design is opened or cut again, follows its datum (which it holds), undoes, and is saved with the model. geometry.face.split.delete removes it. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo
model: face splits along datum planes (#508 )
2026-10-16 15:27:03 -04:00 · 2026-10-16 15:14:54 -04:00 · 2026-10-16 15:14:54 -04:00 · 2026-10-16 14:57:51 -04:00 · 2026-10-16 14:57:51 -04:00 · 2026-10-16 14:57:51 -04:00
355 changed files with 42677 additions and 17180 deletions
@@ -1,2 +1,13 @@
 # Every change to FieldCraft needs the maintainer's review before it merges.
 * @jyviko
+
+# Release and supply-chain paths, named explicitly so they stay owner-reviewed if the rule above
+# is ever relaxed: workflows and secrets use, packaging and signing, the updater, dependencies,
+# licences.
+/.github/ @jyviko
+/packaging/ @jyviko
+/crates/update/ @jyviko
+/Cargo.toml @jyviko
+/Cargo.lock @jyviko
+/ATTRIBUTION.md @jyviko
+/deny.toml @jyviko
@@ -41,6 +41,6 @@ body:
    id: version
    attributes:
      label: Version and platform
-      placeholder: "v0.5.9 (or commit), macOS 15 arm64"
+      placeholder: "v0.6.0 (or commit), macOS 15 arm64"
    validations:
      required: true
@@ -1,13 +1,14 @@
 FieldCraft is open-source CAE pre-processing in Rust: it turns geometry into analysis-ready
 finite element models, writes Abaqus, Nastran and LS-DYNA decks, and solves linear static and
 modal problems with its own solver. AI agents can drive it over MCP (`fieldcraft-cli mcp`).
-[README](https://github.com/jyviko/fieldcraft#readme) ·
-[roadmap](https://github.com/jyviko/fieldcraft/blob/main/ROADMAP.md) ·
-[issues](https://github.com/jyviko/fieldcraft/issues)
+[README](https://github.com/tangency-labs/fieldcraft#readme) ·
+[roadmap](https://github.com/tangency-labs/fieldcraft/blob/main/ROADMAP.md) ·
+[issues](https://github.com/tangency-labs/fieldcraft/issues)

 **Which file?**
 - **macOS 11+** (Apple silicon and Intel): open `fieldcraft-{version}-macos-universal.dmg` and
-  drag `FieldCraft.app` onto Applications. The command-line tool is in
+  drag `FieldCraft.app` onto Applications. The command-line tool is included at
+  `/Applications/FieldCraft.app/Contents/MacOS/fieldcraft-cli` and also available separately in
  `fieldcraft-cli-{version}-macos-universal.zip`.
 - **Linux** (x86_64, glibc 2.35+: Ubuntu 22.04, Debian 12, Fedora 36 or newer):
  `fieldcraft-{version}-linux-x86_64.AppImage` (`chmod +x`, then run it), or unpack
@@ -6,6 +6,13 @@ name: CI
 # Pull requests from forks (outside contributors) run the full gate, once the maintainer approves
 # the run, so the review sees it; so do Dependabot's (.github/dependabot.yml), which nobody tests
 # locally. The heavy job stays off pull requests.
+#
+# What runs when (docs/releasing.md, "What CI runs when"): the `plan` job picks a base, the last
+# `develop` commit whose CI run passed (a pull request: its merge base; nightly and manual runs:
+# none), and `cargo xtask affected` maps the change since it to crates. `cargo xtask ci --affected`
+# then lints and tests those crates and their dependents only; the heavy and oracle jobs run when
+# the change reaches the solvers, the oracle or everything (Cargo.toml/Cargo.lock/xtask/workflows).
+# Nightly and manual runs, and every release (release.yml), run all of it.
 on:
  pull_request:
    paths:
@@ -26,7 +33,7 @@ on:
      - 'docs/features.md'
      - 'docs/oracle.md'
  schedule:
-    # Nightly, on the default branch (develop): the heavy tests.
+    # Nightly, on the default branch (develop): the whole gate, the heavy tests and the oracle.
    - cron: '23 3 * * *'
    # Weekly: the oracle on macOS too, so results that differ by platform show up in CI (the
    # fixtures are often blessed on a Mac; #115).
@@ -37,7 +44,8 @@ permissions:
  contents: read

 # A newer merge cancels the run still going for the one before it, so a burst of merges is tested
-# once, at the tip. Nightly and manual runs are grouped apart and never cancelled by a merge.
+# once, at the tip; nothing is missed, since the tip's run tests everything since the last green
+# run. Nightly and manual runs are grouped apart and never cancelled by a merge.
 concurrency:
  group: ci-${{ github.ref }}-${{ github.event_name }}
  cancel-in-progress: ${{ github.event_name == 'push' || github.event_name == 'pull_request' }}
@@ -46,32 +54,101 @@ env:
  CARGO_TERM_COLOR: always

 jobs:
+  plan:
+    name: Plan (affected crates)
+    if: github.event.schedule != '41 4 * * 0' && (github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name != github.repository || github.event.pull_request.user.login == 'dependabot[bot]')
+    runs-on: ubuntu-24.04
+    timeout-minutes: 15
+    permissions:
+      contents: read
+      # To find the last green run on develop.
+      actions: read
+    outputs:
+      base: ${{ steps.base.outputs.base }}
+      everything: ${{ steps.affected.outputs.everything }}
+      solver: ${{ steps.affected.outputs.solver }}
+      wasm: ${{ steps.affected.outputs.wasm }}
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          fetch-depth: 0
+      - uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2.9.2
+        with:
+          key: plan
+          save-if: ${{ github.ref == 'refs/heads/develop' }}
+      - name: Pick the base
+        id: base
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          EVENT: ${{ github.event_name }}
+          PR_BASE: ${{ github.base_ref }}
+        run: |
+          base=""
+          case "$EVENT" in
+            push)
+              # The newest develop commit whose push run passed and that this commit contains.
+              # Runs that were cancelled or failed are skipped, so their changes are tested here.
+              for sha in $(gh api "repos/$GITHUB_REPOSITORY/actions/workflows/ci.yml/runs?branch=develop&event=push&status=success&per_page=100" --jq '.workflow_runs[].head_sha'); do
+                if [ "$sha" != "$GITHUB_SHA" ] && git merge-base --is-ancestor "$sha" HEAD; then
+                  base="$sha"
+                  break
+                fi
+              done
+              ;;
+            pull_request)
+              base="$(git merge-base "origin/$PR_BASE" HEAD || true)"
+              ;;
+          esac
+          # Nightly and manual runs, or no green run to start from: everything.
+          echo "base=$base" >>"$GITHUB_OUTPUT"
+          echo "### Base: \`${base:-none (everything)}\`" >>"$GITHUB_STEP_SUMMARY"
+      - name: cargo xtask affected
+        id: affected
+        env:
+          BASE: ${{ steps.base.outputs.base }}
+        run: |
+          if [ -n "$BASE" ]; then
+            cargo xtask affected --base "$BASE" --github-output | tee -a "$GITHUB_STEP_SUMMARY"
+          else
+            printf 'everything=true\nsolver=true\nwasm=true\n' >>"$GITHUB_OUTPUT"
+          fi
+
  ci:
    name: cargo xtask ci
-    if: github.event.schedule != '41 4 * * 0' && (github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name != github.repository || github.event.pull_request.user.login == 'dependabot[bot]')
+    needs: plan
    runs-on: ubuntu-24.04
    timeout-minutes: 60
    steps:
      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          fetch-depth: 0
      - uses: dtolnay/rust-toolchain@stable
        with:
          components: rustfmt, clippy
          targets: wasm32-unknown-unknown
      - uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2.9.2
        with:
+          # Shared keys: release.yml's verify jobs restore these caches (they save only on main).
+          shared-key: ci
          save-if: ${{ github.ref == 'refs/heads/develop' }}
-      # A dependency update changes THIRD-PARTY-LICENSES.txt, which Dependabot cannot regenerate:
-      # regenerate it here so the gate checks everything else, and dependabot-licences.yml commits
-      # it to the pull request.
-      - name: Regenerate THIRD-PARTY-LICENSES.txt (Dependabot)
-        if: github.event.pull_request.user.login == 'dependabot[bot]'
-        run: cargo xtask licences
-      - run: cargo xtask ci
+      - name: Software GPU (lavapipe), so headless snapshots run the GPU pipeline
+        run: sudo apt-get update -q && sudo apt-get install -y -q --no-install-recommends mesa-vulkan-drivers libvulkan1
+      - name: cargo xtask ci (the affected crates, or everything)
+        env:
+          BASE: ${{ needs.plan.outputs.base }}
+          # The drawing tests run on lavapipe and fail, instead of skipping, without it.
+          FIELDCRAFT_GPU: software
+          FIELDCRAFT_REQUIRE_GPU: "1"
+        run: |
+          if [ -n "$BASE" ]; then cargo xtask ci --affected "$BASE"; else cargo xtask ci; fi

  heavy:
-    # The heavy verification and corpus tests (#[ignore]d) and the doc tests.
+    # The heavy verification and corpus tests (#[ignore]d) and the doc tests, when the change
+    # reaches them.
    name: cargo xtask test --heavy
-    if: github.event.schedule != '41 4 * * 0' && github.event_name != 'pull_request'
+    needs: plan
+    if: github.event_name != 'pull_request' && (needs.plan.outputs.solver == 'true' || needs.plan.outputs.everything == 'true')
    runs-on: ubuntu-24.04
    timeout-minutes: 60
    steps:
@@ -79,15 +156,18 @@ jobs:
      - uses: dtolnay/rust-toolchain@stable
      - uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2.9.2
        with:
+          shared-key: heavy
          save-if: ${{ github.ref == 'refs/heads/develop' }}
      - run: cargo xtask test --heavy

  oracle:
    # Verification and validation (docs/verification.md): every case against its reference and
    # its fixture, and docs/oracle.md must be the table the cases produce. Cases marked `slow`
-    # run here too while the whole set stays within a few minutes; `--quick` skips them.
+    # run here too while the whole set stays within a few minutes; `--quick` skips them. It runs
+    # when the change reaches the solvers or the oracle's package.
    name: cargo xtask oracle
-    if: github.event.schedule != '41 4 * * 0' && (github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name != github.repository || github.event.pull_request.user.login == 'dependabot[bot]')
+    needs: plan
+    if: needs.plan.outputs.solver == 'true' || needs.plan.outputs.everything == 'true'
    runs-on: ubuntu-24.04
    timeout-minutes: 45
    steps:
@@ -95,7 +175,7 @@ jobs:
      - uses: dtolnay/rust-toolchain@stable
      - uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2.9.2
        with:
-          key: oracle
+          shared-key: oracle
          save-if: ${{ github.ref == 'refs/heads/develop' }}
      - run: cargo xtask oracle
      - name: docs/oracle.md is current
@@ -113,14 +193,31 @@ jobs:
      - uses: dtolnay/rust-toolchain@stable
      - uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2.9.2
        with:
-          key: oracle-macos
+          shared-key: oracle-macos
          save-if: ${{ github.ref == 'refs/heads/develop' }}
      - run: cargo xtask oracle
      - name: docs/oracle.md is current
        run: git diff --exit-code docs/oracle.md

+  windows:
+    # The desktop app's tests on Windows, nightly and on demand: the Windows-only code
+    # (apps/fieldcraft/src/native_crash.rs, the exception filter) builds and a child process that
+    # faults on purpose leaves its native crash report (#299). Releases build Windows too.
+    name: Windows app tests
+    if: github.event.schedule == '23 3 * * *' || github.event_name == 'workflow_dispatch'
+    runs-on: windows-latest
+    timeout-minutes: 60
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2.9.2
+        with:
+          shared-key: windows
+          save-if: ${{ github.ref == 'refs/heads/develop' }}
+      - run: cargo test --locked --profile ci -p fieldcraft
+
  advisories:
-    name: Dependency advisories and sources
+    name: Dependency licences, advisories and sources
    if: github.event.schedule != '41 4 * * 0' && (github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name != github.repository || github.event.pull_request.user.login == 'dependabot[bot]')
    runs-on: ubuntu-24.04
    timeout-minutes: 20
@@ -129,4 +226,4 @@ jobs:
      - uses: dtolnay/rust-toolchain@stable
      - name: Install cargo-deny
        run: cargo install cargo-deny --version 0.20.2 --locked
-      - run: cargo deny --locked check --warn unmaintained advisories bans sources
+      - run: cargo deny --locked check --warn unmaintained advisories bans licenses sources
@@ -1,40 +0,0 @@
-# Dependabot's Cargo updates change THIRD-PARTY-LICENSES.txt (`cargo xtask licences`), which
-# Dependabot cannot regenerate: this commits the regenerated file to its pull request. CI's own
-# run on the pull request regenerates it too, so its result covers everything else.
-name: Dependabot licences
-
-on:
-  pull_request:
-    branches: [develop]
-    paths: [Cargo.lock]
-
-permissions:
-  contents: write
-
-concurrency:
-  group: dependabot-licences-${{ github.head_ref }}
-  cancel-in-progress: true
-
-jobs:
-  licences:
-    if: github.event.pull_request.user.login == 'dependabot[bot]'
-    runs-on: ubuntu-24.04
-    timeout-minutes: 20
-    steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
-        with:
-          ref: ${{ github.head_ref }}
-      - uses: dtolnay/rust-toolchain@stable
-      - run: cargo xtask licences
-      - name: Commit the regenerated file
-        run: |
-          if git diff --quiet -- THIRD-PARTY-LICENSES.txt; then
-            echo "THIRD-PARTY-LICENSES.txt is up to date"
-            exit 0
-          fi
-          git config user.name "github-actions[bot]"
-          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
-          # [skip ci]: the pull request's CI run already regenerated this file and tested the
-          # tree with it; a bot-authored commit would otherwise wait for a maintainer's approval.
-          git commit -m "deps: regenerate THIRD-PARTY-LICENSES.txt [skip ci]" -- THIRD-PARTY-LICENSES.txt
-          git push origin "HEAD:${GITHUB_HEAD_REF}"
@@ -1,4 +1,4 @@
-# The web app (apps/fieldcraft-web, docs/web.md) on GitHub Pages: https://jyviko.github.io/fieldcraft/
+# The web app (apps/fieldcraft-web, docs/web.md) on GitHub Pages: https://tangency-labs.github.io/fieldcraft/
 # After SolidCraft's pages.yml (MIT OR Apache-2.0; see ATTRIBUTION.md).
 #
 # A push to `main` (a release; main holds released code only) builds the app with Trunk (release,
@@ -33,6 +33,10 @@ env:

 jobs:
  build:
+    # POSTHOG_KEY lives in the `release` environment (main only, docs/releasing.md). The deploy job
+    # already uses github-pages and a job has one environment, so the build job reads the key: on
+    # main it runs in `release`, elsewhere in no environment and with an empty key.
+    environment: ${{ github.ref == 'refs/heads/main' && 'release' || '' }}
    runs-on: ubuntu-24.04
    timeout-minutes: 60
    steps:
@@ -6,8 +6,9 @@
 # DRAFT GitHub Release "FieldCraft v<version>", with SHA256SUMS.txt (signed with the release key
 # into SHA256SUMS.txt.minisig when the FIELDCRAFT_SIGNING_KEY secret exists) and generated notes. The
 # version is [workspace.package] version in Cargo.toml; a suffix (0.2.0-rc.1) makes a
-# pre-release. A person verifies the draft and publishes it; this workflow never publishes,
-# and pushes to develop or tags never start it.
+# pre-release. Every package, and the release itself, carries THIRD-PARTY-LICENSES.txt, generated
+# here by `cargo xtask licences` (it is not committed). A person verifies the draft and publishes
+# it; this workflow never publishes, and pushes to develop or tags never start it.
 #
 #   macOS universal (arm64 + x86_64)   .dmg with FieldCraft.app, the CLI as a .zip   packaging/macos
 #   Linux x86_64 (glibc 2.35+)         .tar.gz, .AppImage, .deb and .rpm              packaging/linux
@@ -16,7 +17,14 @@
 # macOS: signed with a Developer ID and notarized when the APPLE_* secrets exist, ad-hoc
 # otherwise (the release notes say which). Linux and Windows builds are not signed.
 #
-# Dry run: `gh workflow run release.yml --ref <branch>` builds everything and uploads the
+# The verify jobs run everything CI can: the full `cargo xtask ci`, `cargo xtask test --heavy` and
+# `cargo xtask oracle` on Linux, and the oracle on macOS. Develop's CI tests only what each change
+# affects (ci.yml), so this is where a release proves all of it. The packaging jobs build in
+# parallel with them and only upload workflow artifacts; the `release` job, the only one that
+# signs SHA256SUMS.txt or touches a GitHub Release, needs every verify and packaging job, so a
+# failing verify means no draft and no signature.
+#
+# Dry run: `gh workflow run release.yml --ref <branch>` verifies and builds everything and uploads the
 # `release-assets` artifact without creating a release. `-f draft=true` on `main` retries
 # the draft.
 name: Release
@@ -40,8 +48,10 @@ concurrency:
  cancel-in-progress: false

 env:
+  # The same CARGO_* environment as ci.yml: rust-cache hashes it into the cache key, so a
+  # difference would stop the verify jobs restoring develop's caches. (rust-cache already sets
+  # CARGO_INCREMENTAL=0 for every job.)
  CARGO_TERM_COLOR: always
-  CARGO_INCREMENTAL: 0

 jobs:
  version:
@@ -70,9 +80,68 @@ jobs:
          { echo "version=$VERSION"; echo "prerelease=$pre"; echo "draft=$REQUEST_DRAFT"; } >>"$GITHUB_OUTPUT"
          echo "### FieldCraft v$VERSION (\`${GITHUB_SHA::9}\`)" >>"$GITHUB_STEP_SUMMARY"

+  # The full gate, the heavy tests and the oracle on Linux and macOS: the `release` job needs them,
+  # so a release never drafts or signs a commit that fails any of them. Each restores the cache of
+  # its ci.yml counterpart on develop (same shared-key), so it starts warm.
+  verify-ci:
+    name: Verify (cargo xtask ci)
+    runs-on: ubuntu-24.04
+    timeout-minutes: 60
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          components: rustfmt, clippy
+          targets: wasm32-unknown-unknown
+      - uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2.9.2
+        with:
+          shared-key: ci
+          # Release runs are rare: only release-branch runs keep a cache, so dry runs don't evict CI's.
+          save-if: ${{ github.ref == 'refs/heads/main' }}
+      - run: cargo xtask ci
+
+  verify-heavy:
+    name: Verify (cargo xtask test --heavy)
+    runs-on: ubuntu-24.04
+    timeout-minutes: 60
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2.9.2
+        with:
+          shared-key: heavy
+          save-if: ${{ github.ref == 'refs/heads/main' }}
+      - run: cargo xtask test --heavy
+
+  verify-oracle:
+    name: Verify (cargo xtask oracle, ${{ matrix.os }})
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: ubuntu-24.04
+            cache: oracle
+          - os: macos-14
+            cache: oracle-macos
+    runs-on: ${{ matrix.os }}
+    timeout-minutes: 60
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2.9.2
+        with:
+          shared-key: ${{ matrix.cache }}
+          save-if: ${{ github.ref == 'refs/heads/main' }}
+      - run: cargo xtask oracle
+      - name: docs/oracle.md is current
+        run: git diff --exit-code docs/oracle.md
+
  macos:
    name: macOS universal
    needs: version
+    # Signing, notarization and analytics secrets live in the `release` environment, which only
+    # `main` may use; a dry run on another branch asks for no environment and builds unsigned.
+    environment: ${{ github.ref == 'refs/heads/main' && 'release' || '' }}
    runs-on: macos-14
    timeout-minutes: 120
    outputs:
@@ -89,6 +158,8 @@ jobs:
          key: release-macos-universal
          # Release runs are rare: only release-branch runs keep a cache, so dry runs don't evict CI's.
          save-if: ${{ github.ref == 'refs/heads/main' }}
+      - name: Generate THIRD-PARTY-LICENSES.txt (fails when a crate's licence can't be resolved)
+        run: cargo xtask licences
      - name: Import the signing certificate (skipped without APPLE_CERTIFICATE)
        env:
          APPLE_CERTIFICATE: ${{ secrets.APPLE_CERTIFICATE }}
@@ -118,6 +189,9 @@ jobs:
    name: Linux x86_64
    needs: version
    # The oldest GitHub-hosted image, so the binaries need only glibc >= 2.35.
+    # Signing, notarization and analytics secrets live in the `release` environment, which only
+    # `main` may use; a dry run on another branch asks for no environment and builds unsigned.
+    environment: ${{ github.ref == 'refs/heads/main' && 'release' || '' }}
    runs-on: ubuntu-22.04
    timeout-minutes: 90
    env:
@@ -137,6 +211,8 @@ jobs:
          key: release-linux-x86_64
          # Release runs are rare: only release-branch runs keep a cache, so dry runs don't evict CI's.
          save-if: ${{ github.ref == 'refs/heads/main' }}
+      - name: Generate THIRD-PARTY-LICENSES.txt (fails when a crate's licence can't be resolved)
+        run: cargo xtask licences
      - name: Install cargo-deb and cargo-generate-rpm
        run: |
          cargo install --locked --version "$CARGO_DEB_VERSION" cargo-deb
@@ -201,6 +277,9 @@ jobs:
  windows:
    name: Windows x64
    needs: version
+    # Signing, notarization and analytics secrets live in the `release` environment, which only
+    # `main` may use; a dry run on another branch asks for no environment and builds unsigned.
+    environment: ${{ github.ref == 'refs/heads/main' && 'release' || '' }}
    runs-on: windows-latest
    timeout-minutes: 90
    env:
@@ -215,6 +294,8 @@ jobs:
          key: release-windows-x64
          # Release runs are rare: only release-branch runs keep a cache, so dry runs don't evict CI's.
          save-if: ${{ github.ref == 'refs/heads/main' }}
+      - name: Generate THIRD-PARTY-LICENSES.txt (fails when a crate's licence can't be resolved)
+        run: cargo xtask licences
      - name: Build and package (zip)
        shell: pwsh
        env:
@@ -229,7 +310,11 @@ jobs:

  release:
    name: Draft release (or dry-run artifacts)
-    needs: [version, macos, linux, windows]
+    # The only job that publishes anything: it waits for every verify and packaging job.
+    needs: [version, verify-ci, verify-heavy, verify-oracle, macos, linux, windows]
+    # Signing, notarization and analytics secrets live in the `release` environment, which only
+    # `main` may use; a dry run on another branch asks for no environment and builds unsigned.
+    environment: ${{ github.ref == 'refs/heads/main' && 'release' || '' }}
    runs-on: ubuntu-24.04
    permissions:
      contents: write
@@ -246,12 +331,16 @@ jobs:
          pattern: release-*
          path: artifacts
          merge-multiple: true
+      - uses: dtolnay/rust-toolchain@stable
+      # The same file every package carries, attached to the release on its own.
+      - name: Generate THIRD-PARTY-LICENSES.txt
+        run: cargo xtask licences && cp THIRD-PARTY-LICENSES.txt artifacts/
      - name: Check the set and write the checksums
        run: |
          for f in "fieldcraft-$VERSION-macos-universal.dmg" "fieldcraft-cli-$VERSION-macos-universal.zip" \
            "fieldcraft-$VERSION-linux-x86_64.tar.gz" "fieldcraft-$VERSION-linux-x86_64.AppImage" \
            "fieldcraft_${VERSION}_amd64.deb" "fieldcraft-$VERSION.x86_64.rpm" \
-            "fieldcraft-$VERSION-windows-x64.zip"; do
+            "fieldcraft-$VERSION-windows-x64.zip" THIRD-PARTY-LICENSES.txt; do
            test -s "artifacts/$f" || { echo "::error::missing $f"; exit 1; }
          done
          (cd artifacts && sha256sum -- * | tee SHA256SUMS.txt)
@@ -7,3 +7,4 @@
 .DS_Store
 *.swp
 __pycache__/
+/THIRD-PARTY-LICENSES.txt
@@ -24,7 +24,9 @@ FieldCraft everywhere: crates `fieldcraft-*`, binaries `fieldcraft` and `fieldcr
 ## Never crash
 People trust FieldCraft with their models; a crash loses their work. **This outranks feature work.**
 - **No panics in non-test code:** no `unwrap()`, `expect()`, `panic!`, `unreachable!`, `todo!`,
-  `unimplemented!`; no `unsafe` (`unsafe_code = "forbid"`).
+  `unimplemented!`; no `unsafe` (`unsafe_code = "forbid"`). The one exception, in the app crate
+  (which denies it instead), has no safe API: the Windows-only `apps/fieldcraft/src/native_crash.rs`
+  (the exception filter that records crashes inside native code such as graphics drivers).
 - **Errors are `Result<T, E>`** through the crate's error type and `?`. An unfinished feature
  returns an error ("not supported yet: …"); it never panics.
 - **Input-derived numbers are hostile** (command parameters, model files, solver decks,
@@ -119,20 +121,25 @@ People trust FieldCraft with their models; a crash loses their work. **This outr
     contributors' pull requests wait for the maintainer's review (CONTRIBUTING.md). Never squash.
     Then remove your worktree and delete your local branch.
  5. Never run the full gate locally: no `cargo xtask ci`, no `cargo clippy --workspace`, no
-     `cargo xtask wasm` or `oracle` unless step 2 calls for it. Never watch CI. GitHub CI runs
-     `cargo xtask ci` (fmt, assets, licences, layers, clippy -D warnings, tests, wasm), the
-     oracle, the heavy tests and the advisories once per merge on `develop`; the coordinator
+     `cargo xtask wasm` or `oracle` unless step 2 calls for it. Never watch CI. GitHub CI runs,
+     per merge on `develop`, `cargo xtask ci --affected <last green commit>` (fmt, assets,
+     layers on the whole tree; clippy and tests on the crates the change reaches; wasm when one
+     of them builds for it), the oracle and heavy tests when the change reaches the solvers or
+     the oracle, and the dependency licences and advisories; a change to Cargo.toml, Cargo.lock,
+     xtask or the workflows, the nightly run and every release run all of it (docs/releasing.md,
+     "What CI runs when"). `cargo xtask affected --base origin/develop` shows what your branch
+     reaches. The coordinator
     watches it and sends a failure back to the change that caused it, which is fixed forward
     at once.
 - **Keep the trunk gate fast** (under ~3 minutes on CI). A test that takes more than a few seconds
  (convergence studies, the whole corpus, cross-checks between solvers) is
  `#[ignore = "heavy: cargo xtask test --heavy (CI heavy job)"]`, with a fast representative
  test left in the trunk gate. The `heavy` CI job runs `cargo xtask test --heavy` (every ignored
-  test, benchmarks included, and the doc tests) on every merge to `develop`, nightly and on
-  demand (`gh workflow run CI --ref <branch>`). Hostile-input tests run commands on sessions with small
+  test, benchmarks included, and the doc tests) on merges to `develop` that reach a crate with
+  heavy tests, nightly, before every release and on demand (`gh workflow run CI --ref <branch>`). Hostile-input tests run commands on sessions with small
  work caps (`Session::limits`) so refusals are instant; never lower the production caps for a
  test.
- **Publishing**: `origin` is github.com/jyviko/fieldcraft. Changes land through pull requests
+- **Publishing**: `origin` is github.com/tangency-labs/fieldcraft. Changes land through pull requests
  as the workflow above describes; the coordinator reads every merged diff and sends findings
  back as fix-forward work. Never force-push `develop` or `main`; `main` holds released code and moves only by
  fast-forward at a release (docs/releasing.md). Never commit `plan/`, `.agent-files/`,
@@ -24,13 +24,26 @@ is committed and listed here with its exports.
 | docs/media/examples/bracket-hex.png | FieldCraft contributors | Original: the FieldCraft window captured (`ui.capture`) with the solved bracket-hex sample (docs/examples.md) | MIT OR Apache-2.0 |
 | docs/media/examples/crank-arm.png | FieldCraft contributors | Original: the FieldCraft window captured (`ui.capture`) with the solved crank-arm sample (docs/examples.md) | MIT OR Apache-2.0 |
 | docs/media/examples/crank-mirror.png | FieldCraft contributors | Original: the FieldCraft window captured (`ui.capture`) with the solved crank-mirror sample (docs/examples.md) | MIT OR Apache-2.0 |
-| crates/ui-egui/thumbnails/bracket-hex.png | FieldCraft contributors | Original: the viewport of docs/media/examples/bracket-hex.png cropped to the model and scaled to 320 px wide (ImageMagick, 128-colour palette), the bracket-hex sample's thumbnail on the Start card | MIT OR Apache-2.0 |
-| crates/ui-egui/thumbnails/crank-arm.png | FieldCraft contributors | Original: the viewport of docs/media/examples/crank-arm.png cropped to the model and scaled to 320 px wide (ImageMagick, 128-colour palette), the crank-arm sample's thumbnail on the Start card | MIT OR Apache-2.0 |
-| crates/ui-egui/thumbnails/crank-mirror.png | FieldCraft contributors | Original: the viewport of docs/media/examples/crank-mirror.png cropped to the model and scaled to 320 px wide (ImageMagick, 128-colour palette), the crank-mirror sample's thumbnail on the Start card | MIT OR Apache-2.0 |
-| crates/ui-egui/thumbnails/drop-test.png | FieldCraft contributors | Original: the viewport of docs/media/examples/drop-test.png cropped to the model and scaled to 320 px wide (ImageMagick, 128-colour palette), the drop-test sample's thumbnail on the Start card | MIT OR Apache-2.0 |
-| crates/ui-egui/thumbnails/heated-bracket.png | FieldCraft contributors | Original: the viewport of docs/media/examples/heated-bracket.png cropped to the model and scaled to 320 px wide (ImageMagick, 128-colour palette), the heated-bracket sample's thumbnail on the Start card | MIT OR Apache-2.0 |
-| crates/ui-egui/thumbnails/rubber-seal.png | FieldCraft contributors | Original: the viewport of docs/media/examples/rubber-seal.png cropped to the model and scaled to 320 px wide (ImageMagick, 128-colour palette), the rubber-seal sample's thumbnail on the Start card | MIT OR Apache-2.0 |
+| docs/meshing/skill/analytic-cylinder.png, docs/meshing/skill/analytic-pipe.png, docs/meshing/skill/analytic-plate-hole.png, docs/meshing/skill/analytic-sphere.png, docs/meshing/skill/analytic-torus.png, docs/meshing/skill/bent-tube.png, docs/meshing/skill/bolted-assembly.png, docs/meshing/skill/cantilever-i-beam.png, docs/meshing/skill/crank-arm.png, docs/meshing/skill/cup.png, docs/meshing/skill/filleted-bracket-blocks.png, docs/meshing/skill/filleted-bracket.png, docs/meshing/skill/i-beam.png, docs/meshing/skill/loft-transition.png, docs/meshing/skill/perforated-plate.png, docs/meshing/skill/pi5-base.png, docs/meshing/skill/pi5-lid.png, docs/meshing/skill/pinhole-block.png, docs/meshing/skill/plain-cup.png, docs/meshing/skill/rounded-box.png, docs/meshing/skill/shallow-groove.png, docs/meshing/skill/sharp-wedge.png, docs/meshing/skill/sphere-on-plate.png, docs/meshing/skill/spline-vase.png, docs/meshing/skill/stepped-block.png, docs/meshing/skill/thin-ribs.png, docs/meshing/skill/thin-wall-enclosure.png, docs/meshing/skill/upright-bracket.png | FieldCraft contributors | Original: section pictures of the corpus parts and samples meshed by the meshing skill, drawn by `fieldcraft-cli snapshot` (`cargo xtask skill-results`, docs/meshing/skill-results.md) | MIT OR Apache-2.0 |
+| docs/media/examples/flow-past.png | FieldCraft contributors | Original: the FieldCraft window captured (`ui.capture`) with the flow-past sample (its bracket; the viewport does not draw flow results yet) (docs/examples.md) | MIT OR Apache-2.0 |
+| docs/media/examples/cantilever.png | FieldCraft contributors | Original: the FieldCraft window captured (`ui.capture`) with the solved cantilever sample (docs/examples.md) | MIT OR Apache-2.0 |
+| docs/media/examples/impact.png | FieldCraft contributors | Original: the FieldCraft window captured (`ui.capture`) with the solved impact sample (docs/examples.md) | MIT OR Apache-2.0 |
+| docs/media/examples/ibeam.png | FieldCraft contributors | Original: the FieldCraft window captured (`ui.capture`) with the solved ibeam sample (docs/examples.md) | MIT OR Apache-2.0 |
+| crates/ui-egui/thumbnails/ibeam.png | FieldCraft contributors | Original: the solved ibeam sample rendered by FieldCraft (`ui.render`, light theme), cropped to the model and scaled to 320 px wide (ImageMagick, 128-colour palette), the ibeam sample's thumbnail on the Start card | MIT OR Apache-2.0 |
+| docs/media/examples/parts.png | FieldCraft contributors | Original: the FieldCraft window captured (`ui.capture`) with the parts sample (meshes only, nothing to solve) (docs/examples.md) | MIT OR Apache-2.0 |
+| crates/ui-egui/thumbnails/flow-past.png | FieldCraft contributors | Original: the flow-past sample as docs/media/examples/flow-past.png shows it, rendered by FieldCraft (`ui.render`, light theme), cropped to the model and scaled to 320 px wide (ImageMagick, 128-colour palette), the flow-past sample's thumbnail on the Start card | MIT OR Apache-2.0 |
+| crates/ui-egui/thumbnails/cantilever.png | FieldCraft contributors | Original: the cantilever sample as docs/media/examples/cantilever.png shows it, rendered by FieldCraft (`ui.render`, light theme), cropped to the model and scaled to 320 px wide (ImageMagick, 128-colour palette), the cantilever sample's thumbnail on the Start card | MIT OR Apache-2.0 |
+| crates/ui-egui/thumbnails/impact.png | FieldCraft contributors | Original: the impact sample as docs/media/examples/impact.png shows it, rendered by FieldCraft (`ui.render`, light theme), cropped to the model and scaled to 320 px wide (ImageMagick, 128-colour palette), the impact sample's thumbnail on the Start card | MIT OR Apache-2.0 |
+| crates/ui-egui/thumbnails/parts.png | FieldCraft contributors | Original: the parts sample as docs/media/examples/parts.png shows it, rendered by FieldCraft (`ui.render`, light theme), cropped to the model and scaled to 320 px wide (ImageMagick, 128-colour palette), the parts sample's thumbnail on the Start card | MIT OR Apache-2.0 |
+| crates/ui-egui/thumbnails/bracket-hex.png | FieldCraft contributors | Original: the bracket-hex sample as docs/media/examples/bracket-hex.png shows it, rendered by FieldCraft (`ui.render`, light theme), cropped to the model and scaled to 320 px wide (ImageMagick, 128-colour palette), the bracket-hex sample's thumbnail on the Start card | MIT OR Apache-2.0 |
+| crates/ui-egui/thumbnails/crank-arm.png | FieldCraft contributors | Original: the crank-arm sample as docs/media/examples/crank-arm.png shows it, rendered by FieldCraft (`ui.render`, light theme), cropped to the model and scaled to 320 px wide (ImageMagick, 128-colour palette), the crank-arm sample's thumbnail on the Start card | MIT OR Apache-2.0 |
+| crates/ui-egui/thumbnails/crank-mirror.png | FieldCraft contributors | Original: the crank-mirror sample as docs/media/examples/crank-mirror.png shows it, rendered by FieldCraft (`ui.render`, light theme), cropped to the model and scaled to 320 px wide (ImageMagick, 128-colour palette), the crank-mirror sample's thumbnail on the Start card | MIT OR Apache-2.0 |
+| crates/ui-egui/thumbnails/drop-test.png | FieldCraft contributors | Original: the drop-test sample as docs/media/examples/drop-test.png shows it, rendered by FieldCraft (`ui.render`, light theme), cropped to the model and scaled to 320 px wide (ImageMagick, 128-colour palette), the drop-test sample's thumbnail on the Start card | MIT OR Apache-2.0 |
+| crates/ui-egui/thumbnails/heated-bracket.png | FieldCraft contributors | Original: the heated-bracket sample as docs/media/examples/heated-bracket.png shows it, rendered by FieldCraft (`ui.render`, light theme), cropped to the model and scaled to 320 px wide (ImageMagick, 128-colour palette), the heated-bracket sample's thumbnail on the Start card | MIT OR Apache-2.0 |
+| crates/ui-egui/thumbnails/rubber-seal.png | FieldCraft contributors | Original: the rubber-seal sample as docs/media/examples/rubber-seal.png shows it, rendered by FieldCraft (`ui.render`, light theme), cropped to the model and scaled to 320 px wide (ImageMagick, 128-colour palette), the rubber-seal sample's thumbnail on the Start card | MIT OR Apache-2.0 |
 | crates/decks/tests/golden/nastran/*.bdf | FieldCraft contributors | Written by our Nastran writer from our own test models (crates/decks/tests/nastran.rs) | MIT OR Apache-2.0 |
+| crates/engine/tests/designs/pi5-enclosure.json | FieldCraft contributors | Original SolidCraft recipe (solid.* commands) of an enclosure for a single-board computer, for thermal analysis: base, lid, heat sink, board, chips, connectors and the air inside | MIT OR Apache-2.0 |
+| crates/geometry/tests/designs/hollow-box.solidcraft, crates/geometry/tests/designs/hollow-box-post.solidcraft, crates/geometry/tests/designs/open-tray-post.solidcraft | FieldCraft contributors | Built with `solidcraft-cli run` from the recipes beside them (crates/geometry/tests/designs/*.json) | MIT OR Apache-2.0 |
 | assets/icons/assembly.instance.svg, assets/icons/assembly.instance.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/assembly.instance.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/deck.read.svg, assets/icons/deck.read.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/deck.read.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/deck.write.abaqus.svg, assets/icons/deck.write.abaqus.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/deck.write.abaqus.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
@@ -44,6 +57,7 @@ is committed and listed here with its exports.
 | assets/icons/file.save_as.svg, assets/icons/file.save_as.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/file.save_as.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/file.save.svg, assets/icons/file.save.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/file.save.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/geometry.bodies.svg, assets/icons/geometry.bodies.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/geometry.bodies.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
+| assets/icons/geometry.check.svg, assets/icons/geometry.check.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/geometry.check.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/geometry.datum.svg, assets/icons/geometry.datum.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/geometry.datum.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/geometry.datum.axis.svg, assets/icons/geometry.datum.axis.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/geometry.datum.axis.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/geometry.datum.point.svg, assets/icons/geometry.datum.point.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/geometry.datum.point.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
@@ -51,6 +65,10 @@ is committed and listed here with its exports.
 | assets/icons/geometry.midsurface.svg, assets/icons/geometry.midsurface.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/geometry.midsurface.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/geometry.open.svg, assets/icons/geometry.open.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/geometry.open.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/geometry.partition.svg, assets/icons/geometry.partition.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/geometry.partition.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
+| assets/icons/geometry.faces.merge.svg, assets/icons/geometry.faces.merge.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/geometry.faces.merge.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
+| assets/icons/geometry.face.absorb.svg, assets/icons/geometry.face.absorb.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/geometry.face.absorb.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
+| assets/icons/geometry.face.split.svg, assets/icons/geometry.face.split.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/geometry.face.split.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
+| assets/icons/geometry.stitch.svg, assets/icons/geometry.stitch.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/geometry.stitch.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/geometry.tessellate.svg, assets/icons/geometry.tessellate.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/geometry.tessellate.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/interaction.bolt.svg, assets/icons/interaction.bolt.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/interaction.bolt.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/interaction.connector.svg, assets/icons/interaction.connector.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/interaction.connector.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
@@ -58,6 +76,8 @@ is committed and listed here with its exports.
 | assets/icons/interaction.contact.general.svg, assets/icons/interaction.contact.general.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/interaction.contact.general.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/interaction.contact.pair.svg, assets/icons/interaction.contact.pair.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/interaction.contact.pair.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/interaction.fsi.svg, assets/icons/interaction.fsi.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/interaction.fsi.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
+| assets/icons/mesh.block.svg, assets/icons/mesh.block.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.block.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
+| assets/icons/mesh.mirror.svg, assets/icons/mesh.mirror.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.mirror.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/model.mass.create.svg, assets/icons/model.mass.create.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/model.mass.create.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/interaction.rigid_wall.svg, assets/icons/interaction.rigid_wall.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/interaction.rigid_wall.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/model.spring.create.svg, assets/icons/model.spring.create.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/model.spring.create.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
@@ -74,9 +94,13 @@ is committed and listed here with its exports.
 | assets/icons/mesh.layers.svg, assets/icons/mesh.layers.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.layers.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/mesh.node.add.svg, assets/icons/mesh.node.add.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.node.add.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/mesh.node.merge.svg, assets/icons/mesh.node.merge.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.node.merge.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
+| assets/icons/mesh.node.relax.svg, assets/icons/mesh.node.relax.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.node.relax.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/mesh.order.quadratic.svg, assets/icons/mesh.order.quadratic.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.order.quadratic.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/mesh.quad.faces.svg, assets/icons/mesh.quad.faces.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.quad.faces.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/mesh.quality.svg, assets/icons/mesh.quality.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.quality.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
+| assets/icons/mesh.quality.mark.svg, assets/icons/mesh.quality.mark.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.quality.mark.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
+| assets/icons/results.export.vtu.svg, assets/icons/results.export.vtu.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/results.export.vtu.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
+| assets/icons/mesh.export.stl.svg, assets/icons/mesh.export.stl.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.export.stl.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/mesh.region.remesh.svg, assets/icons/mesh.region.remesh.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.region.remesh.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/mesh.size.adapt.svg, assets/icons/mesh.size.adapt.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.size.adapt.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/mesh.size.global.svg, assets/icons/mesh.size.global.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.size.global.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
@@ -85,6 +109,8 @@ is committed and listed here with its exports.
 | assets/icons/mesh.surface.check.svg, assets/icons/mesh.surface.check.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.surface.check.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/mesh.tag.svg, assets/icons/mesh.tag.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.tag.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/mesh.tet.generate.svg, assets/icons/mesh.tet.generate.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.tet.generate.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
+| assets/icons/mesh.hex.extrude.svg, assets/icons/mesh.hex.extrude.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.hex.extrude.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
+| assets/icons/mesh.plan.svg, assets/icons/mesh.plan.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.plan.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/mesh.planar.svg, assets/icons/mesh.planar.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.planar.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/mesh.transition.svg, assets/icons/mesh.transition.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.transition.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
 | assets/icons/mesh.untangle.svg, assets/icons/mesh.untangle.vectorcraft | FieldCraft contributors | Original toolbar icon drawn with VectorCraft from `assets/icons/src/mesh.untangle.json` (`cargo xtask icons`) | MIT OR Apache-2.0 |
@@ -182,12 +208,12 @@ is committed and listed here with its exports.
 | clippy.toml, rustfmt.toml | SolidCraft | MIT OR Apache-2.0 |
 | crates/geometry/src/tagged_mesh.rs (package and part reading, transforms, units, caps) | SolidCraft `crates/io/src/threemf.rs` | MIT OR Apache-2.0 |
 | crates/render/src/camera.rs, crates/render/src/raster.rs | SolidCraft `crates/render/src/camera.rs`, `raster.rs` | MIT OR Apache-2.0 |
-| crates/ui-egui/src/gpu.rs, crates/ui-egui/src/theme.rs (tokens and their values), crates/ui-egui/src/control.rs, crates/ui-egui/src/lib.rs (input injection, screenshots), crates/ui-egui/src/toolbar.rs (workspace switcher, tabs, panels with drop-downs, fitting), crates/ui-egui/src/appbar.rs (application bar; the mark is drawn from assets/app-icon/icon-small.svg's coordinates), crates/ui-egui/src/titlebar.rs (caption buttons, drag and resize zones; SolidCraft took it from VectorCraft), crates/ui-egui/src/frame.rs (windows, heading bands), crates/ui-egui/src/browser.rs (row drawing), crates/ui-egui/src/palette.rs (command line and search), crates/ui-egui/src/timeline.rs (timeline strip, transport), crates/ui-egui/src/viewport.rs (navigation bar, orientation gizmo), crates/ui-egui/src/files.rs (background opening, file pickers as host services) | SolidCraft `crates/ui-egui/src/` (titlebar.rs also VectorCraft `crates/ui-egui/src/titlebar.rs`) | MIT OR Apache-2.0 |
+| crates/gpu/src/view.rs (viewport pipelines and shaders), crates/ui-egui/src/gpu.rs, crates/ui-egui/src/theme.rs (tokens and their values), crates/ui-egui/src/control.rs, crates/ui-egui/src/lib.rs (input injection, screenshots), crates/ui-egui/src/toolbar.rs (workspace switcher, tabs, panels with drop-downs, fitting), crates/ui-egui/src/appbar.rs (application bar; the mark is drawn from assets/app-icon/icon-small.svg's coordinates), crates/ui-egui/src/titlebar.rs (caption buttons, drag and resize zones; SolidCraft took it from VectorCraft), crates/ui-egui/src/frame.rs (windows, heading bands), crates/ui-egui/src/browser.rs (row drawing), crates/ui-egui/src/palette.rs (command line and search), crates/ui-egui/src/timeline.rs (timeline strip, transport), crates/ui-egui/src/viewport.rs (navigation bar, orientation gizmo), crates/ui-egui/src/files.rs (background opening, file pickers as host services) | SolidCraft `crates/ui-egui/src/` (titlebar.rs also VectorCraft `crates/ui-egui/src/titlebar.rs`) | MIT OR Apache-2.0 |
 | crates/ui-egui/src/navigation.rs (navigation presets and bindings), crates/ui-egui/src/viewport.rs (orbit about the point under the cursor, or the drawn centre from empty space; Ctrl + left drag orbits) | SolidCraft `crates/ui-egui/src/prefs.rs` (`NavPreset`, `NavBinding`, `NAV_PRESETS`, `orbit`) | MIT OR Apache-2.0 |
 | crates/ui-egui/src/fields.rs (form rows: a label column of fixed width, then the field) | SolidCraft `crates/ui-egui/src/dialogs.rs` | MIT OR Apache-2.0 |
 | crates/io/src/fs.rs (atomic writes) | SolidCraft `crates/io/src/safe_write.rs` | MIT OR Apache-2.0 |
 | crates/io/src/recovery.rs (recovery folder, entries, locks) | SolidCraft `crates/engine/src/recovery.rs` | MIT OR Apache-2.0 |
-| crates/engine/src/crash.rs, crates/engine/src/crash_tests.rs (crash reports: panic hook, locked command journal, unclean-exit detection, report folders and limits, replay), apps/fieldcraft-cli/src/crashes.rs, docs/crash-reports.md (structure) | SolidCraft `crates/engine/src/crash.rs`, `crash_tests.rs`, `apps/solidcraft-cli/src/crashes.rs`, `docs/crash-reports.md` | MIT OR Apache-2.0 |
+| crates/engine/src/crash.rs, crates/engine/src/crash_tests.rs (crash reports: panic hook, locked command journal, unclean-exit detection, startup steps, native crash reports, report folders and limits, replay), apps/fieldcraft/src/native_crash.rs (Windows exception filter and minidump), apps/fieldcraft-cli/src/crashes.rs, docs/crash-reports.md (structure) | SolidCraft `crates/engine/src/crash.rs`, `crash_tests.rs`, `apps/solidcraft/src/native_crash.rs`, `apps/solidcraft-cli/src/crashes.rs`, `docs/crash-reports.md` | MIT OR Apache-2.0 |
 | apps/fieldcraft/src/control_server.rs | SolidCraft `apps/solidcraft/src/control_server.rs` | MIT OR Apache-2.0 |
 | crates/mcp/src/ (JSON-RPC framing, MCP lifecycle, tool schema checks, the control-channel backend, base64) | SolidCraft `crates/mcp/src/` | MIT OR Apache-2.0 |
 | crates/io/src/roots.rs (the rules of read and write roots) | VectorCraft's automation roots (docs/mcp.md there) | MIT OR Apache-2.0 |
@@ -15,7 +15,7 @@ needed most, and how to claim work. The rules every change follows, by a person
 You need stable Rust 1.95 or newer.

 ```sh
-git clone https://github.com/jyviko/fieldcraft && cd fieldcraft
+git clone https://github.com/tangency-labs/fieldcraft && cd fieldcraft
 cargo run --release -p fieldcraft -- --sample cantilever   # the desktop app on a sample model
 cargo run -p fieldcraft-cli -- commands                    # every command and its parameters
 cargo test -p fieldcraft-solver                            # the tests of one crate
@@ -28,32 +28,32 @@ cargo xtask oracle --quick                                 # the verification ca

 ## Where help is wanted most

-See the [`help wanted`](https://github.com/jyviko/fieldcraft/labels/help%20wanted) and
-[`good first issue`](https://github.com/jyviko/fieldcraft/labels/good%20first%20issue) labels, and
+See the [`help wanted`](https://github.com/tangency-labs/fieldcraft/labels/help%20wanted) and
+[`good first issue`](https://github.com/tangency-labs/fieldcraft/labels/good%20first%20issue) labels, and
 the `area:` labels for your field. In order of how much they would help users:

-1. **Reproducible meshes** ([#115](https://github.com/jyviko/fieldcraft/issues/115)). The same part
+1. **Reproducible meshes** ([#115](https://github.com/tangency-labs/fieldcraft/issues/115)). The same part
   must give the same tet mesh on every platform and every run, as the solvers already do.
-2. **All-hex meshing of thin and curved parts** ([#85](https://github.com/jyviko/fieldcraft/issues/85)).
+2. **All-hex meshing of thin and curved parts** ([#85](https://github.com/tangency-labs/fieldcraft/issues/85)).
   The octree mesher over-refines thin walls; concave transition templates and an up-front depth
   are next. Hex meshing is the centre of gravity of the project.
-3. **Getting results in and out**: ParaView export ([#90](https://github.com/jyviko/fieldcraft/issues/90)),
-   Gmsh import ([#91](https://github.com/jyviko/fieldcraft/issues/91)), Abaqus deck reading
-   ([#98](https://github.com/jyviko/fieldcraft/issues/98)), CSV and STL
-   ([#92](https://github.com/jyviko/fieldcraft/issues/92), [#93](https://github.com/jyviko/fieldcraft/issues/93)).
-4. **Verification benchmarks** ([#97](https://github.com/jyviko/fieldcraft/issues/97),
-   [#106](https://github.com/jyviko/fieldcraft/issues/106)). An engineer with a published benchmark
+3. **Getting results in and out**: ParaView export ([#90](https://github.com/tangency-labs/fieldcraft/issues/90)),
+   Gmsh import ([#91](https://github.com/tangency-labs/fieldcraft/issues/91)), Abaqus deck reading
+   ([#98](https://github.com/tangency-labs/fieldcraft/issues/98)), CSV and STL
+   ([#92](https://github.com/tangency-labs/fieldcraft/issues/92), [#93](https://github.com/tangency-labs/fieldcraft/issues/93)).
+4. **Verification benchmarks** ([#97](https://github.com/tangency-labs/fieldcraft/issues/97),
+   [#106](https://github.com/tangency-labs/fieldcraft/issues/106)). An engineer with a published benchmark
   can add it as an oracle case without touching solver code.
 5. **Nonlinear elements and materials**: incompatible modes at finite strain
-   ([#82](https://github.com/jyviko/fieldcraft/issues/82)), kinematic hardening
-   ([#81](https://github.com/jyviko/fieldcraft/issues/81)), and the material library
-   ([#99](https://github.com/jyviko/fieldcraft/issues/99)).
-6. **The app**: typed command forms ([#112](https://github.com/jyviko/fieldcraft/issues/112)), XY and
-   path plots ([#94](https://github.com/jyviko/fieldcraft/issues/94), [#95](https://github.com/jyviko/fieldcraft/issues/95)).
+   ([#82](https://github.com/tangency-labs/fieldcraft/issues/82)), kinematic hardening
+   ([#81](https://github.com/tangency-labs/fieldcraft/issues/81)), and the material library
+   ([#99](https://github.com/tangency-labs/fieldcraft/issues/99)).
+6. **The app**: typed command forms ([#112](https://github.com/tangency-labs/fieldcraft/issues/112)), XY and
+   path plots ([#94](https://github.com/tangency-labs/fieldcraft/issues/94), [#95](https://github.com/tangency-labs/fieldcraft/issues/95)).

 Bigger areas on the [roadmap](ROADMAP.md) — contact, dynamics, composites, coupled fields, wave
 propagation, turbulence — are open to anyone who wants to own one: start a thread in
-[Discussions](https://github.com/jyviko/fieldcraft/discussions).
+[Discussions](https://github.com/tangency-labs/fieldcraft/discussions).

 ## Before you start: claim an issue

@@ -425,12 +425,6 @@ version = "1.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f2032f911046de80f0a198e0901378627c33f59ea0ac00e363d481118bd70a53"

-[[package]]
-name = "base64"
-version = "0.22.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "72b3254f16251a8381aa12e40e3c4d2f0199f8c6508fbecb9d91f575e0fbb8c6"
-
 [[package]]
 name = "base64"
 version = "0.23.1"
@@ -1052,7 +1046,7 @@ dependencies = [
 [[package]]
 name = "egui-wgpu"
 version = "0.36.2"
-source = "git+https://github.com/bherbruck/solidcraft?rev=a629236650c44ee73edf36fab0dcd2385103a610#a629236650c44ee73edf36fab0dcd2385103a610"
+source = "git+https://github.com/bherbruck/solidcraft?rev=b1695873f5d0031f51a8d5e7ec036fced6f000e2#b1695873f5d0031f51a8d5e7ec036fced6f000e2"
 dependencies = [
 "ahash",
 "bytemuck",
@@ -1270,7 +1264,7 @@ checksum = "b97b65636e5b9ef369943878ac74335ba1c55c1cb6adbf1e2c293c624248d693"

 [[package]]
 name = "fieldcraft"
-version = "0.5.9"
+version = "0.6.0"
 dependencies = [
 "eframe",
 "egui",
@@ -1279,28 +1273,33 @@ dependencies = [
 "fieldcraft-io",
 "fieldcraft-ui-egui",
 "fieldcraft-update",
- "getrandom 0.3.4",
+ "getrandom 0.4.3",
 "log",
 "rfd",
 "rustls",
 "serde_json",
+ "signal-hook",
 "ureq",
+ "windows-sys 0.61.2",
 ]

 [[package]]
 name = "fieldcraft-cli"
-version = "0.5.9"
+version = "0.6.0"
 dependencies = [
 "fieldcraft-engine",
+ "fieldcraft-gpu",
 "fieldcraft-io",
 "fieldcraft-mcp",
+ "fieldcraft-render",
 "fieldcraft-update",
+ "png",
 "serde_json",
 ]

 [[package]]
 name = "fieldcraft-decks"
-version = "0.5.9"
+version = "0.6.0"
 dependencies = [
 "fieldcraft-model",
 "serde_json",
@@ -1309,7 +1308,7 @@ dependencies = [

 [[package]]
 name = "fieldcraft-engine"
-version = "0.5.9"
+version = "0.6.0"
 dependencies = [
 "fieldcraft-decks",
 "fieldcraft-explicit",
@@ -1328,12 +1327,12 @@ dependencies = [
 "serde",
 "serde_json",
 "thiserror 2.0.21",
- "zip",
+ "zip 9.0.3",
 ]

 [[package]]
 name = "fieldcraft-explicit"
-version = "0.5.9"
+version = "0.6.0"
 dependencies = [
 "fieldcraft-fem",
 "fieldcraft-model",
@@ -1344,7 +1343,7 @@ dependencies = [

 [[package]]
 name = "fieldcraft-fem"
-version = "0.5.9"
+version = "0.6.0"
 dependencies = [
 "fieldcraft-model",
 "thiserror 2.0.21",
@@ -1352,10 +1351,11 @@ dependencies = [

 [[package]]
 name = "fieldcraft-geometry"
-version = "0.5.9"
+version = "0.6.0"
 dependencies = [
 "fieldcraft-model",
- "quick-xml",
+ "quick-xml 0.42.0",
+ "serde",
 "serde_json",
 "solidcraft-doc",
 "solidcraft-engine",
@@ -1363,12 +1363,24 @@ dependencies = [
 "solidcraft-io",
 "solidcraft-kernel",
 "thiserror 2.0.21",
- "zip",
+ "zip 9.0.3",
+]
+
+[[package]]
+name = "fieldcraft-gpu"
+version = "0.6.0"
+dependencies = [
+ "fieldcraft-render",
+ "log",
+ "pollster 1.0.1",
+ "serde_json",
+ "thiserror 2.0.21",
+ "wgpu",
 ]

 [[package]]
 name = "fieldcraft-io"
-version = "0.5.9"
+version = "0.6.0"
 dependencies = [
 "fieldcraft-model",
 "log",
@@ -1376,12 +1388,12 @@ dependencies = [
 "serde_json",
 "sha2 0.11.1",
 "thiserror 2.0.21",
- "zip",
+ "zip 9.0.3",
 ]

 [[package]]
 name = "fieldcraft-lbm"
-version = "0.5.9"
+version = "0.6.0"
 dependencies = [
 "fieldcraft-mesh",
 "fieldcraft-model",
@@ -1391,9 +1403,10 @@ dependencies = [

 [[package]]
 name = "fieldcraft-mcp"
-version = "0.5.9"
+version = "0.6.0"
 dependencies = [
 "fieldcraft-engine",
+ "fieldcraft-gpu",
 "fieldcraft-io",
 "fieldcraft-render",
 "fieldcraft-testkit",
@@ -1402,7 +1415,7 @@ dependencies = [

 [[package]]
 name = "fieldcraft-mesh"
-version = "0.5.9"
+version = "0.6.0"
 dependencies = [
 "fieldcraft-model",
 "num-bigint",
@@ -1414,7 +1427,7 @@ dependencies = [

 [[package]]
 name = "fieldcraft-model"
-version = "0.5.9"
+version = "0.6.0"
 dependencies = [
 "serde",
 "serde_json",
@@ -1423,14 +1436,14 @@ dependencies = [

 [[package]]
 name = "fieldcraft-parallel"
-version = "0.5.9"
+version = "0.6.0"
 dependencies = [
 "rayon",
 ]

 [[package]]
 name = "fieldcraft-render"
-version = "0.5.9"
+version = "0.6.0"
 dependencies = [
 "fieldcraft-model",
 "png",
@@ -1440,7 +1453,7 @@ dependencies = [

 [[package]]
 name = "fieldcraft-solver"
-version = "0.5.9"
+version = "0.6.0"
 dependencies = [
 "fieldcraft-fem",
 "fieldcraft-mesh",
@@ -1452,7 +1465,7 @@ dependencies = [

 [[package]]
 name = "fieldcraft-testkit"
-version = "0.5.9"
+version = "0.6.0"
 dependencies = [
 "fieldcraft-engine",
 "fieldcraft-geometry",
@@ -1463,7 +1476,7 @@ dependencies = [

 [[package]]
 name = "fieldcraft-ui-egui"
-version = "0.5.9"
+version = "0.6.0"
 dependencies = [
 "craft-ui",
 "egui",
@@ -1472,6 +1485,7 @@ dependencies = [
 "fieldcraft-engine",
 "fieldcraft-explicit",
 "fieldcraft-geometry",
+ "fieldcraft-gpu",
 "fieldcraft-model",
 "fieldcraft-render",
 "fieldcraft-update",
@@ -1484,7 +1498,7 @@ dependencies = [

 [[package]]
 name = "fieldcraft-update"
-version = "0.5.9"
+version = "0.6.0"
 dependencies = [
 "flate2",
 "log",
@@ -1496,14 +1510,14 @@ dependencies = [
 "tar",
 "thiserror 2.0.21",
 "ureq",
- "zip",
+ "zip 9.0.3",
 ]

 [[package]]
 name = "fieldcraft-web"
-version = "0.5.9"
+version = "0.6.0"
 dependencies = [
- "base64 0.22.1",
+ "base64",
 "eframe",
 "egui",
 "fieldcraft-engine",
@@ -2208,7 +2222,7 @@ checksum = "f9f8bd3e56ce4dfc153cf470fffbfa98c7620958b312ca5c3a4b8d5181fd13c6"
 [[package]]
 name = "matext4cgmath"
 version = "0.1.0"
-source = "git+https://github.com/bherbruck/solidcraft?rev=a629236650c44ee73edf36fab0dcd2385103a610#a629236650c44ee73edf36fab0dcd2385103a610"
+source = "git+https://github.com/bherbruck/solidcraft?rev=b1695873f5d0031f51a8d5e7ec036fced6f000e2#b1695873f5d0031f51a8d5e7ec036fced6f000e2"
 dependencies = [
 "cgmath",
 "katexit",
@@ -2241,9 +2255,9 @@ dependencies = [

 [[package]]
 name = "minisign"
-version = "0.9.1"
+version = "0.10.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "aefd422a7a8b5efced01cd7cdf3771e62ebecbc90e3d27695002d3af6af94586"
+checksum = "3062dbbf4d8f57899e2252804f7512a4fd89c8211c58fa6c786d38794a0c809d"
 dependencies = [
 "ct-codecs",
 "getrandom 0.4.3",
@@ -2355,6 +2369,18 @@ dependencies = [
 "jni-sys 0.3.1",
 ]

+[[package]]
+name = "nix"
+version = "0.31.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cf20d2fde8ff38632c426f1165ed7436270b44f199fc55284c38276f9db47c3d"
+dependencies = [
+ "bitflags 2.13.2",
+ "cfg-if",
+ "cfg_aliases",
+ "libc",
+]
+
 [[package]]
 name = "nohash-hasher"
 version = "0.2.0"
@@ -3087,6 +3113,15 @@ dependencies = [
 "memchr",
 ]

+[[package]]
+name = "quick-xml"
+version = "0.42.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "41b1177fdf999d2321d3fb46ff47159d9c1fb9ad66a4879f8c50a0b504615e9b"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "quote"
 version = "1.0.47"
@@ -3639,6 +3674,16 @@ version = "2.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f8fadd59c855ef2080decdef8ff161eb6661b86933c9d82e5ba29dc602a55aba"

+[[package]]
+name = "signal-hook"
+version = "0.4.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b29ffa27d3d59a049bb328258de100f8012848d1b08d444e08bbc02ac468435e"
+dependencies = [
+ "libc",
+ "signal-hook-registry",
+]
+
 [[package]]
 name = "signal-hook-registry"
 version = "1.4.8"
@@ -3792,7 +3837,7 @@ dependencies = [
 [[package]]
 name = "solidcraft-doc"
 version = "0.11.0"
-source = "git+https://github.com/bherbruck/solidcraft?rev=a629236650c44ee73edf36fab0dcd2385103a610#a629236650c44ee73edf36fab0dcd2385103a610"
+source = "git+https://github.com/bherbruck/solidcraft?rev=b1695873f5d0031f51a8d5e7ec036fced6f000e2#b1695873f5d0031f51a8d5e7ec036fced6f000e2"
 dependencies = [
 "log",
 "serde",
@@ -3809,7 +3854,7 @@ dependencies = [
 [[package]]
 name = "solidcraft-engine"
 version = "0.11.0"
-source = "git+https://github.com/bherbruck/solidcraft?rev=a629236650c44ee73edf36fab0dcd2385103a610#a629236650c44ee73edf36fab0dcd2385103a610"
+source = "git+https://github.com/bherbruck/solidcraft?rev=b1695873f5d0031f51a8d5e7ec036fced6f000e2#b1695873f5d0031f51a8d5e7ec036fced6f000e2"
 dependencies = [
 "log",
 "serde",
@@ -3826,7 +3871,7 @@ dependencies = [
 [[package]]
 name = "solidcraft-geom"
 version = "0.11.0"
-source = "git+https://github.com/bherbruck/solidcraft?rev=a629236650c44ee73edf36fab0dcd2385103a610#a629236650c44ee73edf36fab0dcd2385103a610"
+source = "git+https://github.com/bherbruck/solidcraft?rev=b1695873f5d0031f51a8d5e7ec036fced6f000e2#b1695873f5d0031f51a8d5e7ec036fced6f000e2"
 dependencies = [
 "serde",
 "thiserror 2.0.21",
@@ -3835,9 +3880,9 @@ dependencies = [
 [[package]]
 name = "solidcraft-io"
 version = "0.11.0"
-source = "git+https://github.com/bherbruck/solidcraft?rev=a629236650c44ee73edf36fab0dcd2385103a610#a629236650c44ee73edf36fab0dcd2385103a610"
+source = "git+https://github.com/bherbruck/solidcraft?rev=b1695873f5d0031f51a8d5e7ec036fced6f000e2#b1695873f5d0031f51a8d5e7ec036fced6f000e2"
 dependencies = [
- "quick-xml",
+ "quick-xml 0.41.0",
 "serde",
 "serde_json",
 "sha2 0.10.9",
@@ -3845,13 +3890,13 @@ dependencies = [
 "solidcraft-geom",
 "solidcraft-kernel",
 "thiserror 2.0.21",
- "zip",
+ "zip 3.0.0",
 ]

 [[package]]
 name = "solidcraft-kernel"
 version = "0.11.0"
-source = "git+https://github.com/bherbruck/solidcraft?rev=a629236650c44ee73edf36fab0dcd2385103a610#a629236650c44ee73edf36fab0dcd2385103a610"
+source = "git+https://github.com/bherbruck/solidcraft?rev=b1695873f5d0031f51a8d5e7ec036fced6f000e2#b1695873f5d0031f51a8d5e7ec036fced6f000e2"
 dependencies = [
 "log",
 "rayon",
@@ -3870,9 +3915,10 @@ dependencies = [
 [[package]]
 name = "solidcraft-render"
 version = "0.11.0"
-source = "git+https://github.com/bherbruck/solidcraft?rev=a629236650c44ee73edf36fab0dcd2385103a610#a629236650c44ee73edf36fab0dcd2385103a610"
+source = "git+https://github.com/bherbruck/solidcraft?rev=b1695873f5d0031f51a8d5e7ec036fced6f000e2#b1695873f5d0031f51a8d5e7ec036fced6f000e2"
 dependencies = [
 "image",
+ "png",
 "serde",
 "solidcraft-geom",
 ]
@@ -3880,7 +3926,7 @@ dependencies = [
 [[package]]
 name = "solidcraft-sketch"
 version = "0.11.0"
-source = "git+https://github.com/bherbruck/solidcraft?rev=a629236650c44ee73edf36fab0dcd2385103a610#a629236650c44ee73edf36fab0dcd2385103a610"
+source = "git+https://github.com/bherbruck/solidcraft?rev=b1695873f5d0031f51a8d5e7ec036fced6f000e2#b1695873f5d0031f51a8d5e7ec036fced6f000e2"
 dependencies = [
 "serde",
 "solidcraft-geom",
@@ -4228,7 +4274,7 @@ dependencies = [
 [[package]]
 name = "truck-meshalgo"
 version = "0.4.0"
-source = "git+https://github.com/bherbruck/solidcraft?rev=a629236650c44ee73edf36fab0dcd2385103a610#a629236650c44ee73edf36fab0dcd2385103a610"
+source = "git+https://github.com/bherbruck/solidcraft?rev=b1695873f5d0031f51a8d5e7ec036fced6f000e2#b1695873f5d0031f51a8d5e7ec036fced6f000e2"
 dependencies = [
 "array-macro",
 "derive_more",
@@ -4278,7 +4324,7 @@ dependencies = [
 [[package]]
 name = "truck-shapeops"
 version = "0.4.0"
-source = "git+https://github.com/bherbruck/solidcraft?rev=a629236650c44ee73edf36fab0dcd2385103a610#a629236650c44ee73edf36fab0dcd2385103a610"
+source = "git+https://github.com/bherbruck/solidcraft?rev=b1695873f5d0031f51a8d5e7ec036fced6f000e2#b1695873f5d0031f51a8d5e7ec036fced6f000e2"
 dependencies = [
 "derive_more",
 "itertools 0.13.0",
@@ -4293,7 +4339,7 @@ dependencies = [
 [[package]]
 name = "truck-stepio"
 version = "0.3.0"
-source = "git+https://github.com/bherbruck/solidcraft?rev=a629236650c44ee73edf36fab0dcd2385103a610#a629236650c44ee73edf36fab0dcd2385103a610"
+source = "git+https://github.com/bherbruck/solidcraft?rev=b1695873f5d0031f51a8d5e7ec036fced6f000e2#b1695873f5d0031f51a8d5e7ec036fced6f000e2"
 dependencies = [
 "chrono",
 "truck-geometry",
@@ -4333,6 +4379,12 @@ dependencies = [
 "rustc-hash 2.1.3",
 ]

+[[package]]
+name = "typed-path"
+version = "0.12.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8e28f89b80c87b8fb0cf04ab448d5dd0dd0ade2f8891bae878de66a75a28600e"
+
 [[package]]
 name = "typenum"
 version = "1.20.1"
@@ -4386,7 +4438,7 @@ version = "3.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9a7ac20be9b7726e0bbdbf974c059676d9acb1cd414961f570a4e8231cacd7fc"
 dependencies = [
- "base64 0.23.1",
+ "base64",
 "log",
 "percent-encoding",
 "rustls",
@@ -4402,7 +4454,7 @@ version = "0.6.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f86fd172ccca569e458f61b6bdd6220965a9ef36e672a6852953b51a0e1583be"
 dependencies = [
- "base64 0.23.1",
+ "base64",
 "http",
 "httparse",
 "log",
@@ -4697,7 +4749,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "338e30461b3a2b67d70eb30a6d89f8e0c93a833e07d2ae89085cd070c4a00ac0"
 dependencies = [
 "proc-macro2",
- "quick-xml",
+ "quick-xml 0.41.0",
 "quote",
 ]

@@ -5356,7 +5408,7 @@ checksum = "e450f9b2ed1dff33c94c12589a87338689467b9c4f5d8a5710bd09a847d2c8a7"

 [[package]]
 name = "xtask"
-version = "0.5.9"
+version = "0.6.0"
 dependencies = [
 "serde_json",
 ]
@@ -5507,6 +5559,21 @@ dependencies = [
 "zopfli",
 ]

+[[package]]
+name = "zip"
+version = "9.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c2d98561b612a84ae525331a7a094429ef8a5772514ed507ff6db5f54badc971"
+dependencies = [
+ "crc32fast",
+ "flate2",
+ "indexmap",
+ "memchr",
+ "nix",
+ "typed-path",
+ "zopfli",
+]
+
 [[package]]
 name = "zlib-rs"
 version = "0.6.8"
@@ -3,12 +3,12 @@ resolver = "3"
 members = ["crates/*", "apps/*", "xtask"]

 [workspace.package]
-version = "0.5.9"
+version = "0.6.0"
 edition = "2024"
 license = "MIT OR Apache-2.0"
 rust-version = "1.95"
 authors = ["FieldCraft contributors"]
-repository = "https://github.com/jyviko/fieldcraft"
+repository = "https://github.com/tangency-labs/fieldcraft"

 [workspace.dependencies]
 # internal
@@ -28,6 +28,7 @@ fieldcraft-render = { path = "crates/render" }
 fieldcraft-ui-egui = { path = "crates/ui-egui" }
 fieldcraft-mcp = { path = "crates/mcp" }
 fieldcraft-update = { path = "crates/update" }
+fieldcraft-gpu = { path = "crates/gpu" }

 # foundation
 thiserror = "2"
@@ -35,9 +36,9 @@ serde = { version = "1", features = ["derive"] }
 serde_json = { version = "1", features = ["float_roundtrip"] }
 log = "0.4"

-# 3MF packages (docs/formats/tagged-mesh.md): the same versions SolidCraft uses.
-zip = { version = "3", default-features = false, features = ["deflate"] }
-quick-xml = "0.41"
+# 3MF packages (docs/formats/tagged-mesh.md). zip is ahead of SolidCraft (still on 3), so both are built.
+zip = { version = "9", default-features = false, features = ["deflate"] }
+quick-xml = "0.42"

 # content hashes and part checksums of .fieldcraft files (the version SolidCraft uses)
 sha2 = "0.11"
@@ -51,6 +52,9 @@ resvg = { version = "0.48", default-features = false }
 egui = "0.36"
 eframe = { version = "0.36", default-features = false }
 egui-wgpu = "0.36"
+# the wgpu egui-wgpu uses, for the offscreen viewport (crates/gpu); backends come per target there
+wgpu = { version = "30", default-features = false, features = ["std", "wgsl"] }
+pollster = "1.0"
 # Shared Craft-family egui components (icon buttons, tabs, widget palette); the same rev as
 # VectorCraft. MIT OR Apache-2.0.
 craft-ui = { git = "https://github.com/storytold/craft-libs", rev = "5c874d51eeb3de70e735c8ce87a59a7dedd47675" }
@@ -59,13 +63,13 @@ rfd = "0.17"

 # Geometry: SolidCraft's B-rep kernel (MIT OR Apache-2.0), pinned. Only crates/geometry uses it
 # (plan/adr/0001-libraries.md).
-solidcraft-geom = { git = "https://github.com/bherbruck/solidcraft", rev = "a629236650c44ee73edf36fab0dcd2385103a610" }
-solidcraft-kernel = { git = "https://github.com/bherbruck/solidcraft", rev = "a629236650c44ee73edf36fab0dcd2385103a610" }
-solidcraft-doc = { git = "https://github.com/bherbruck/solidcraft", rev = "a629236650c44ee73edf36fab0dcd2385103a610" }
-solidcraft-io = { git = "https://github.com/bherbruck/solidcraft", rev = "a629236650c44ee73edf36fab0dcd2385103a610" }
+solidcraft-geom = { git = "https://github.com/bherbruck/solidcraft", rev = "b1695873f5d0031f51a8d5e7ec036fced6f000e2" }
+solidcraft-kernel = { git = "https://github.com/bherbruck/solidcraft", rev = "b1695873f5d0031f51a8d5e7ec036fced6f000e2" }
+solidcraft-doc = { git = "https://github.com/bherbruck/solidcraft", rev = "b1695873f5d0031f51a8d5e7ec036fced6f000e2" }
+solidcraft-io = { git = "https://github.com/bherbruck/solidcraft", rev = "b1695873f5d0031f51a8d5e7ec036fced6f000e2" }
 # Runs SolidCraft command scripts (the test corpus recipes); only behind fieldcraft-geometry's
 # `scripts` feature.
-solidcraft-engine = { git = "https://github.com/bherbruck/solidcraft", rev = "a629236650c44ee73edf36fab0dcd2385103a610" }
+solidcraft-engine = { git = "https://github.com/bherbruck/solidcraft", rev = "b1695873f5d0031f51a8d5e7ec036fced6f000e2" }

 [workspace.lints.rust]
 unsafe_code = "forbid"
@@ -129,10 +133,10 @@ debug = "line-tables-only"
 # reach a dependent workspace, so FieldCraft applies the same ones from the same pinned commit;
 # keep this list and the rev in step with SolidCraft's [patch.crates-io].
 [patch.crates-io]
-truck-shapeops = { git = "https://github.com/bherbruck/solidcraft", rev = "a629236650c44ee73edf36fab0dcd2385103a610" }
-truck-stepio = { git = "https://github.com/bherbruck/solidcraft", rev = "a629236650c44ee73edf36fab0dcd2385103a610" }
-truck-meshalgo = { git = "https://github.com/bherbruck/solidcraft", rev = "a629236650c44ee73edf36fab0dcd2385103a610" }
-matext4cgmath = { git = "https://github.com/bherbruck/solidcraft", rev = "a629236650c44ee73edf36fab0dcd2385103a610" }
+truck-shapeops = { git = "https://github.com/bherbruck/solidcraft", rev = "b1695873f5d0031f51a8d5e7ec036fced6f000e2" }
+truck-stepio = { git = "https://github.com/bherbruck/solidcraft", rev = "b1695873f5d0031f51a8d5e7ec036fced6f000e2" }
+truck-meshalgo = { git = "https://github.com/bherbruck/solidcraft", rev = "b1695873f5d0031f51a8d5e7ec036fced6f000e2" }
+matext4cgmath = { git = "https://github.com/bherbruck/solidcraft", rev = "b1695873f5d0031f51a8d5e7ec036fced6f000e2" }
 # egui-wgpu with SolidCraft's fixes (vendor/egui-wgpu there): MSAA clamped to what the device
 # supports and 1x on OpenGL adapters, so the requested 4x never fails pipeline validation at start.
-egui-wgpu = { git = "https://github.com/bherbruck/solidcraft", rev = "a629236650c44ee73edf36fab0dcd2385103a610" }
+egui-wgpu = { git = "https://github.com/bherbruck/solidcraft", rev = "b1695873f5d0031f51a8d5e7ec036fced6f000e2" }
@@ -6,7 +6,7 @@ Licensed under the MIT License or the Apache License, Version 2.0, at your optio
 Third-party material

 Software dependencies are listed in Cargo.lock; their licences are in THIRD-PARTY-LICENSES.txt
-(`cargo xtask licences`). Geometry comes from SolidCraft (https://github.com/bherbruck/solidcraft,
+(generated by `cargo xtask licences`, in every release package). Geometry comes from SolidCraft (https://github.com/bherbruck/solidcraft,
 MIT OR Apache-2.0), which builds on the truck crates (https://github.com/ricosjp/truck, Apache-2.0,
 Copyright (c) RICOS Co. Ltd.), some with SolidCraft's modifications.

@@ -10,8 +10,8 @@ see the results — with a nonlinear implicit solver (large deformation, plastic
 in place. Hex meshing is the centre of gravity. Next: buckling and arc-length, contact, then
 the wider material and multiphysics library. See [ROADMAP.md](ROADMAP.md).
 **Want to help?** Pick an issue labelled
-[good first issue](https://github.com/jyviko/fieldcraft/labels/good%20first%20issue) or
-[help wanted](https://github.com/jyviko/fieldcraft/labels/help%20wanted) and read
+[good first issue](https://github.com/tangency-labs/fieldcraft/labels/good%20first%20issue) or
+[help wanted](https://github.com/tangency-labs/fieldcraft/labels/help%20wanted) and read
 [CONTRIBUTING.md](CONTRIBUTING.md).

 ![Claude analyses an I-beam cantilever in FieldCraft over MCP: it opens the part, hex meshes it, sets steel, the clamp and a 1 kN tip load, solves, shows von Mises stress and the deformed shape, and checks the tip deflection against beam theory](docs/media/claude-mcp.gif)
@@ -28,15 +28,15 @@ theory with shear 0.177 mm).

 ## Download

-[![Download for macOS](https://img.shields.io/badge/macOS-Download-000000?style=for-the-badge&logo=apple&logoColor=white)](https://github.com/jyviko/fieldcraft/releases/latest)
-[![Download for Windows](https://img.shields.io/badge/Windows-Download-0078D6?style=for-the-badge)](https://github.com/jyviko/fieldcraft/releases/latest)
-[![Download for Linux](https://img.shields.io/badge/Linux-Download-FCC624?style=for-the-badge&logo=linux&logoColor=black)](https://github.com/jyviko/fieldcraft/releases/latest)
-[![Try it in your browser](https://img.shields.io/badge/Browser-Try%20it-2ea44f?style=for-the-badge&logo=webassembly&logoColor=white)](https://jyviko.github.io/fieldcraft/)
+[![Download for macOS](https://img.shields.io/badge/macOS-Download-000000?style=for-the-badge&logo=apple&logoColor=white)](https://github.com/tangency-labs/fieldcraft/releases/latest)
+[![Download for Windows](https://img.shields.io/badge/Windows-Download-0078D6?style=for-the-badge)](https://github.com/tangency-labs/fieldcraft/releases/latest)
+[![Download for Linux](https://img.shields.io/badge/Linux-Download-FCC624?style=for-the-badge&logo=linux&logoColor=black)](https://github.com/tangency-labs/fieldcraft/releases/latest)
+[![Try it in your browser](https://img.shields.io/badge/Browser-Try%20it-2ea44f?style=for-the-badge&logo=webassembly&logoColor=white)](https://tangency-labs.github.io/fieldcraft/)

 - **macOS:** open the `.dmg` and drag FieldCraft into Applications (Apple silicon and Intel).
 - **Windows:** unzip and run `fieldcraft.exe`.
 - **Linux:** the `.AppImage` (allow it to run as a program), or the `.tar.gz`.
- **Browser:** [try it at jyviko.github.io/fieldcraft](https://jyviko.github.io/fieldcraft/), no install.
+- **Browser:** [try it at tangency-labs.github.io/fieldcraft](https://tangency-labs.github.io/fieldcraft/), no install.
 - **Command line:** `fieldcraft-cli` ships in every package; AI agents connect to it over MCP
  ([docs/mcp.md](docs/mcp.md)).

@@ -114,10 +114,11 @@ against a closed form or a reference solution ([docs/examples.md](docs/examples.
 ## Build

 ```sh
-cargo xtask ci                                  # fmt, assets, licences, layers, clippy, tests, wasm
+cargo xtask ci                                  # fmt, assets, layers, clippy, tests, wasm
 cargo xtask test --heavy                        # the heavy (ignored) tests and the doc tests
 cargo run -p fieldcraft-cli -- commands         # every command and its parameters
 cargo run -p fieldcraft-cli -- run script.json  # run a command script
+cargo run -p fieldcraft-cli -- snapshot script.json --out shot.png  # draw it to a PNG, no window
 cargo run -p fieldcraft-cli -- mcp              # MCP server on stdio for AI agents (docs/mcp.md)
 ```

@@ -148,7 +149,8 @@ you review and submit yourself, with your session or model attached only if you
 ## License

 Dual-licensed under [MIT](LICENSE-MIT) or [Apache-2.0](LICENSE-APACHE), at your option. Notices
-are in [NOTICE](NOTICE); third-party licences in [THIRD-PARTY-LICENSES.txt](THIRD-PARTY-LICENSES.txt).
+are in [NOTICE](NOTICE); third-party licences in
+THIRD-PARTY-LICENSES.txt, which every release package carries (`cargo xtask licences` writes it).

 FieldCraft is an independent project, not affiliated with, sponsored or endorsed by Dassault
 Systèmes, MSC Software, Siemens or Ansys. Abaqus, Nastran, MSC Nastran, Simcenter Nastran and
@@ -32,7 +32,7 @@ pressure) is a degree of freedom of the existing DOF framework, not a separate s
 | M3 First deck | Sets and surfaces bound to SolidCraft face, edge, vertex and body names, resolved after meshing; materials (isotropic and orthotropic elastic, density) with a unit-system label and consistency check; sections (solid, shell, beam profiles) assigned by set; element formulation per region mapped to each solver; BCs (fixed, displacement, symmetry); loads (force and moment on reference points, pressure, gravity); reference points with kinematic and distributing coupling; steps (linear static, frequency) with explicit per-step load and BC tables and output presets; `model.check` naming every missing or bad item; `model.*` and `mesh.tag` commands (model definition: done); writers for Abaqus input (done: `deck.write`), Nastran SOL 101/103 (done: `deck.write`) and LS-DYNA implicit (done); the `.fieldcraft` file (text definition, binary mesh, geometry references reopened on load, journal; atomic saves, autosave and recovery; undo/redo on the journal: done) | in progress |
 | M4 Own solver and first results | Element library per docs/elements.md (1D and 2D first); Linear static and modal solver (tet4/10, wedge6, hex8, hex20; sparse direct, Lanczos), verified against analytic solutions (solver: done — `fieldcraft-fem` kernels, `fieldcraft-solver` with nested dissection, sparse Cholesky and block Lanczos, `solve.static`/`solve.frequency`/`solve.probe`, patch, cantilever, Lamé, Kirsch and beam-frequency tests; reference points with kinematic and distributing couplings and moments by master–slave constraint elimination, verified by rigid motion, clamping, Saint-Venant tension, bending and tube torsion; 1D elements I: rod2/rod3 trusses, point masses, rotary inertia, springs and dashpots in both solvers and all three decks, verified by the method of joints, the three-bar truss, spring–mass, two-mass chain and torsional pendulum frequencies, and damped decay; 2D elements: plane stress, plane strain and axisymmetric tri3, tri6, quad4 (incompatible modes QM6), quad8 with two degrees of freedom per node, centrifugal loads, `mesh.planar` 2D meshes of polygons and planar faces, verified by patch tests, Kirsch, Lamé (plane strain and axisymmetric), rotating discs and cylinders, and a plane stress cantilever; deck mapping to Abaqus CPS/CPE/CAX, Nastran membranes, LS-DYNA ELFORM 12/13); shells and beams (done: quad4 MITC4 and tri3 MITC3 flat shells with a Hughes–Brezzi drilling rotation, two-node Timoshenko beams with profile properties and orientations, six degrees of freedom at shell and beam nodes shared with solids and trusses, section forces and surface stresses, verified by shell patch tests, Navier's plate, cantilever and portal-frame beams, and the Scordelis–Lo and pinched-cylinder benchmarks); results display (done: `results.*` commands, deformed shape to scale, banded contours of displacement, von Mises, principal and component stresses with a legend, mode shapes with their frequencies and animation, probing a node by clicking it, reaction force and moment sums per set, stale results marked after an edit; explicit steps: field frames by slider or animation with contours per frame, energy histories plotted) | started |
 | M5 Structured hex | 2D quad meshing of faces (`fieldcraft-mesh::quad`: transfinite mapped meshes, free all-quad meshes of polygons with holes on prescribed boundary nodes, exact planar quad validity, shared `SizeField` and even edge divisions; done for planar faces); mapped hex of six-sided regions (trivariate TFI, curved faces) and sweep meshing (multi-level extrusions with imprinted cross-sections, revolutions, one-to-one sweeps through linking faces; interval assignment, hex8/hex20 on the geometry, B-rep face tags, `mesh.hex.generate`/`sweep`/`mapped`: done, 16 of 21 corpus parts all-hex); conforming interfaces between cells (done: `mesh.hex.blocks` meshes a part split with SolidCraft's Split Body into mapped blocks as one conforming mesh — composite faces for seams and tangent faces, interval assignment over all cells, shared faces meshed once, grading off holes and fillets, free-internal-face check; the filleted bracket in 30 cells, hex20 within 0.1 % of a fine tet10 tip deflection); partitions inside FieldCraft (done: datum planes and axes, `geometry.partition` cuts the open design by a datum plane, kept in the model and replayed when the design opens, the two faces of each cut paired by name); cells meshed each with its own method into one mesh (done: `mesh.cells` — hex where a method fits, else tet; matching interfaces merged node for node, others, such as hex next to tet, tied by dual mortar, verified by a tied hex–tet bar in tension to 1e-6); meshing half a symmetric part and mirroring it (done: `mesh.mirror` reflects hex8/hex20/tet4/tet10/wedge6 across a datum plane, right-handed, nodes on the plane merged, tags carried to the image half; a mirrored half bar equals the whole bar's mesh and bending deflection to 1e-12; samples `crank-arm` and `crank-mirror`: one datum, the half extruded in automatic blocks and mirrored, scaled Jacobian ≥ 0.37; or solving the half: `model.boundary_condition.symmetry` on a datum plane, a half bar with half the load bends as the whole to 1e-11); three-sided sweep regions mapped as triangle primitives (done: midpoint subdivision, dominance constraints in interval assignment); automatic blocks of extruded cross-sections (done: `hex::decompose` — holes separated, O-grids, cuts from concave corners and fillets chosen by block quality, kept only when no worse than the free mesh; nothing added to the model); pyramid transitions; automatic decomposition of 3D parts into sweepable and mappable regions | started |
-| M6 Automatic hex | Octree/grid all-hex for any part (first version: done — `fieldcraft-mesh::octree`, `mesh.hex.octree`: 3-refinement grid with conforming templates refined by curvature, thickness and narrow faces, a core cleared to a manifold boundary, feature map onto it, padding and a pillow per patch capturing every sharp curve, foldover-free fitting, certified validity, B-rep face tags; the corpus hex column and the filleted-bracket oracle case; next: transitions for concave refined regions so thin and curved parts stop over-refining); hex-dominant by tet recombination; polycube for blocky parts; layers through thin walls; mesh editing and orphan-mesh import | started |
+| M6 Automatic hex | Octree/grid all-hex for any part (first version: done — `fieldcraft-mesh::octree`, `mesh.hex.octree`: 3-refinement grid with conforming templates refined by curvature, thickness and narrow faces, a core cleared to a manifold boundary, feature map onto it, padding and a pillow per patch capturing every sharp curve, foldover-free fitting, certified validity, B-rep face tags; the corpus hex column and the filleted-bracket oracle case; next: transitions for concave refined regions so thin and curved parts stop over-refining); hex-dominant by tet recombination; polycube for blocky parts; layers through thin walls; mesh editing (node tools done: `mesh.node.merge` equivalences coincident nodes with sets and tags following the survivors and element collapses left out, previewed in its form; `mesh.check.duplicates` lists unmerged nodes, repeated elements, cracks and free edges and selects them; `mesh.renumber` compact, by body or in reverse Cuthill–McKee order, every reference following) and orphan-mesh import | started |
 | M7 Assemblies, contact and friction | Needs M15. Part instances from SolidCraft occurrences; tie between non-matching meshes (mortar: done — `interaction.tie`, dual mortar constraints in the implicit analyses, Abaqus `*TIE` and LS-DYNA tied contact, the tie patch test); implicit contact: surface-to-surface mortar and node-to-surface, penalty and augmented Lagrange, self-contact, automatic pair detection (mortar contact pairs with Coulomb friction in nonlinear static steps: done — segment-to-segment mortar with the consistent tangent by automatic differentiation of the segmentation, augmented Lagrangian with Uzawa updates to a gap tolerance, semismooth active set with a chattering cutback, small sliding without nonlinear geometry and finite sliding with it, overclosure adjusted or refused, Coulomb friction (stick/slip return map, static and kinetic coefficients, symmetrised tangent), pressure, gap, status, shear and slip output; verified by the contact patch test, Hertz cylinder and sphere, Newton's quadratic rate and sliding blocks; the linear analyses refuse contact by name); friction: Coulomb with stick–slip, static/kinetic, anisotropic, pressure-, rate- and temperature-dependent coefficients; contact output (pressure, slip, status); thermal contact conductance and frictional heating; wear (Archard); bolt pretension, connectors with behaviour (elastic, damped, stops, locks); amplitudes, multiple steps, restart; nonlinear steps in all three decks. Verified by Hertz (sphere and cylinder), the Cattaneo–Mindlin partial-slip problem, the sliding block, NAFEMS contact benchmarks | started |
 | M8 Materials, explicit, shells, composites | Plasticity, hyperelasticity, damage data per solver; explicit dynamics decks (Abaqus/Explicit, LS-DYNA); midsurface shells; composite layups and material orientations, continuum shells on swept hex; hybrid (mixed u–p) hex8/hex20/tet10 for nearly incompressible materials (done); heat transfer (solids done: steady and θ-method transient conduction with flux, convection and sources, thermal strain in static steps (solids and 2D) and explicit dynamics (with plasticity), coupled temperature–displacement, `solve.heat`; deck output, 2D/shell/beam conduction planned) | started |
 | M9 Post-processing and deck readers | Results readers for public formats (Nastran OP2, LS-DYNA d3plot, Abaqus `.fil`); XY and path plots, cuts, display groups, free-body forces; deck readers that keep unknown keywords; mesh convergence studies | planned |
@@ -54,6 +54,43 @@ pressure) is a degree of freedom of the existing DOF framework, not a separate s
 | Continuous: performance | CPU first, deterministic: results never depend on the thread count (fixed partitions, sums in a fixed order; checked by hashing results on 1, 2 and 7 threads). Supernodal left-looking Cholesky (11–15× faster than the column solver on one thread), parallel element matrices, stresses and Lanczos products, explicit element updates and LBM cell blocks on rayon threads (done — `fieldcraft-parallel`, `threads` on the solve commands, `FIELDCRAFT_THREADS`); parallel forward/back substitution and explicit tet4 assembly; GPU paths later, within a stated tolerance of the CPU | started |
 | Continuous: desktop and agents | Desktop app (viewport, model tree, commands, control channel, the open design drawn, `ui.capture` of the whole window offscreen: done; toolbar of every capability from the catalogue, ready or coming soon with its milestone, icons drawn with VectorCraft, docs/features.md: done; the Craft-family shell — title bar, workspaces and ribbon drop-downs, browser, context panel, command search, journal timeline, light and dark themes — native file pickers with background opening, drag and drop and recent files, samples and one-click Solve, and an examples gallery of ready-to-solve samples, each checked by a test (docs/examples.md): done; MCP server over stdio, headless or bridged to the app, with read and write roots, docs/mcp.md: done; caps labels in Inter SemiBold; the README's analysis video recorded through MCP by `tools/demo-video`: done; support, load, reference-point and coupling symbols in the viewport and headless renders, with their browser toggles: done; symbols as wireframes, one mark per constrained degree of freedom, a constant size on screen with a size setting, highlighted with their selected definition, concentrated loads drawn over the part: done; selection by picking in the viewport — geometry faces, edges, vertices and bodies, mesh nodes, element faces and elements, box selection, hover, a Target row in command forms, `ui.select`/`ui.selection` and MCP `select`: done; a camera parameter for screenshots, a ribbon that follows the command being run: in progress; the browser build — the same app in a web page with browser file pickers, downloads, drops and autosave to browser storage, deployed to GitHub Pages from each release, docs/web.md: done; in-app updates — a daily check of GitHub Releases, Help › Check for Updates and Reinstall, downloads verified against the release key's signature of SHA256SUMS.txt and swapped in after closing, `app.update.check`, `fieldcraft-cli update`, Reload to update in the browser, docs/updates.md: done), command schema as the public API | started |

+## 0.6.0: the UI/UX release
+
+What landed for 0.6.0 (milestone 0.6.0 on GitHub):
+
+- **Browser:** status checks in one aligned column, Interactions counting ties, a selected set
+  highlighted in the viewport, seeds selectable, editable and deletable, definitions shown with
+  units instead of raw JSON, one highlighted item per context menu, given names shown as typed,
+  and a setup checklist that does not ask for a load on a displacement-driven model or for a
+  support or load on a free body in explicit dynamics (#315, #335, #336, #352, #356, #361, #366).
+- **Results:** units on every legend, summary, probe and reaction sum; legend ranges that can be
+  clamped; max and min markers in the viewport; an energies plot with axes and the current frame;
+  the deformed shape kept when the field changes; a sensible auto scale for large strains; setup
+  symbols off over contours; heat flow through each convection and flux load; probe and reaction
+  results exported to CSV (#92, #191, #319, #321, #325–#332, #362).
+- **Forms, progress and jobs:** solves and meshers run as jobs with their step, stage, count and
+  elapsed time and a Cancel that interrupts every solver and mesher; the control channel and MCP
+  wait for a long solve; mesher forms report what they made; typed fields for label lists, point
+  lists, multi-choices and number-or-auto, JSON fields with hints, defaults shown as set; forms
+  without orphan sets on Cancel; unknown parameters refused (#169, #316, #322–#324, #337, #339,
+  #340, #353, #357, #367, #371).
+- **Picking and preparation:** vertices pickable, selected edges visible over the mesh, a
+  reference point placed by a pick or a hole's centre, Seed Edges switching the filter to edges,
+  live previews and default names for datums and partitions, readable partition cell names, the
+  Partitioned Mesh form with picks and per-cell methods, a mesh marked out of date when its seeds
+  or partitions change, remeshing from the current mesh's settings (#338, #341–#349, #351).
+- **UI conveniences:** File › New (`file.new`), Help › Crash Reports, the I-beam sample, every
+  sample with a Start-card thumbnail and a gallery capture, node tools (merge, duplicates, free
+  edges, renumber), the mesh quality panel's histograms and worst elements, Mirror Mesh and Mesh
+  Block on the ribbon, Rigid Wall in Interactions, readable journal entries and status messages,
+  a sample's name on its document tab, the web build naming an unknown sample (#113, #143, #144,
+  #200, #234, #300, #333, #334, #348, #350, #354, #355, #359, #360, #365).
+- **Mesh soundness:** tet improvement that no longer crowds one vertex, hex20 extrudes that pass
+  the validity gate where hex8 does, biased seeds carried to the opposite edge of a mapped face,
+  designs with a closed internal void and face names over 256 characters meshed (#197, #257,
+  #311, #364, #374).
+- **Heat:** heat transfer across ties for bonded multi-body thermal models (#358).
+
 ## Next

 In progress, in this order of landing:
@@ -3,7 +3,7 @@
 FieldCraft is young; only `main` and the latest release get fixes.

 Please **don't open a public issue** for a security problem. Report it privately through the
-repository's [Security tab](https://github.com/jyviko/fieldcraft/security/advisories/new) with
+repository's [Security tab](https://github.com/tangency-labs/fieldcraft/security/advisories/new) with
 what you found, how to reproduce it (a model, deck or script), the version and platform, and the
 impact you expect.

@@ -1,6 +1,6 @@
 [package]
 name = "fieldcraft-cli"
-description = "FieldCraft from the command line: list commands, run scripts, serve MCP"
+description = "FieldCraft from the command line: list commands, run scripts, draw snapshots, serve MCP"
 version.workspace = true
 edition.workspace = true
 license.workspace = true
@@ -10,10 +10,13 @@ workspace = true

 [dependencies]
 fieldcraft-engine = { workspace = true }
+fieldcraft-gpu = { workspace = true }
+fieldcraft-render = { workspace = true }
 fieldcraft-io = { workspace = true }
 fieldcraft-mcp = { workspace = true }
 fieldcraft-update = { workspace = true }
 serde_json = { workspace = true }

 [dev-dependencies]
+png = { workspace = true }
 fieldcraft-update = { workspace = true, features = ["mock"] }
@@ -1,5 +1,6 @@
 //! fieldcraft-cli commands
 //! fieldcraft-cli run <script.json>
+//! fieldcraft-cli snapshot <script.json> --out shot.png [--view V | --camera JSON] [--size WxH] [--section x|y|z[=V]] [--field F]
 //! fieldcraft-cli features
 //! fieldcraft-cli mcp [--connect ADDR | --headless] [--automation-read-root DIR] [--automation-write-root DIR]
 //! fieldcraft-cli crashes [list [--json] | show <id> | replay <id> | dir | clear [<id>]]
@@ -9,6 +10,7 @@
 #![forbid(unsafe_code)]

 mod crashes;
+mod snapshot;
 mod update;

 use std::path::Path;
@@ -23,6 +25,19 @@ usage:
  fieldcraft-cli commands --json       the same as JSON, each command's parameters as JSON Schema
  fieldcraft-cli run <script.json>     run a script (a JSON array of {\"command\", \"params\"})
                                       and print the model summary
+  fieldcraft-cli snapshot <script.json> --out FILE.png [--view V | --camera JSON]
+                      [--size WxH] [--section x|y|z[=VALUE]] [--field FIELD]
+                                       run a script and draw the model to a PNG with no
+                                       window: the viewport's GPU pipeline on a hardware or
+                                       software GPU, else the CPU rasterizer (FIELDCRAFT_GPU=
+                                       auto|hardware|software|cpu); V: iso (default), x, y, z,
+                                       front, back, left, right, top, bottom; size 1280x800;
+                                       --section hides the elements beyond a plane (at the
+                                       mesh's middle, or VALUE); --field contours a nodal
+                                       field of the solved step (results.contour);
+                                       --camera '{\"yaw\":30,\"pitch\":20,\"target\":...,
+                                       \"fit\":true,\"fov\":35}' aims as MCP screenshot's camera
+                                       (default target: the model's centre of mass)
  fieldcraft-cli features              print docs/features.md (every capability, ready or
                                       coming soon) from the capability catalogue
  fieldcraft-cli mcp [options]         serve the Model Context Protocol on stdin/stdout
@@ -67,6 +82,7 @@ fn main() -> ExitCode {
        Some("mcp") => mcp(args.get(1..).unwrap_or(&[])),
        Some("crashes") => crashes::run(args.get(1..).unwrap_or(&[])),
        Some("update") => update::run(args.get(1..).unwrap_or(&[])),
+        Some("snapshot") => snapshot::run(args.get(1..).unwrap_or(&[])),
        Some("run") => args.get(1).ok_or_else(|| format!("run needs a script\n\n{USAGE}")).and_then(|p| run(p)),
        Some("-V" | "--version") => {
            println!("fieldcraft-cli {}", env!("CARGO_PKG_VERSION"));
@@ -135,7 +151,14 @@ fn mcp(args: &[String]) -> Result<(), String> {
    server.serve(std::io::stdin().lock(), std::io::stdout().lock()).map_err(|e| format!("mcp: {e}"))
 }

-fn run(path: &str) -> Result<(), String> {
+/// The JSON report of a picture: what drew it and what it shows (the MCP `screenshot` reply's
+/// fields).
+pub fn picture_report(r: &fieldcraft_gpu::Renderer, shown: &fieldcraft_engine::view::Shown) -> serde_json::Value {
+    fieldcraft_mcp::picture_report(r, shown)
+}
+
+/// The session after running the script at `path`.
+fn session_of(path: &str) -> Result<Session, String> {
    let size = std::fs::metadata(path).map_err(|e| format!("{path}: {e}"))?.len();
    if size > MAX_SCRIPT_BYTES {
        return Err(format!("{path}: larger than {} MB", MAX_SCRIPT_BYTES / (1024 * 1024)));
@@ -144,6 +167,11 @@ fn run(path: &str) -> Result<(), String> {
    let script: serde_json::Value = serde_json::from_str(&text).map_err(|e| format!("{path}: {e}"))?;
    let mut session = Session::default();
    session.run_script(&script).map_err(|e| e.to_string())?;
+    Ok(session)
+}
+
+fn run(path: &str) -> Result<(), String> {
+    let mut session = session_of(path)?;
    let info = session.execute("model.info", &json!({})).map_err(|e| e.to_string())?;
    println!("{}", serde_json::to_string_pretty(&info).map_err(|e| e.to_string())?);
    Ok(())
@@ -0,0 +1,261 @@
+//! `fieldcraft-cli snapshot`: a script in, a PNG out, with no window and no display. The picture
+//! is the viewport's: the engine's scene ([`fieldcraft_engine::view::frame`]) drawn with the
+//! window's GPU pipelines ([`fieldcraft_gpu::capture`]) on a hardware GPU or a software one
+//! (lavapipe, llvmpipe, WARP), and by the CPU rasterizer as the last tier (`FIELDCRAFT_GPU`,
+//! [`fieldcraft_gpu::select`]).
+
+use fieldcraft_engine::view::{self, Aim, Palette, Section, Target};
+use fieldcraft_gpu::Renderer;
+use fieldcraft_gpu::capture::{self, Capturer};
+use fieldcraft_gpu::select::Policy;
+use fieldcraft_render::{Orientation, StandardView};
+
+/// The picture size when `--size` is not given.
+const DEFAULT_SIZE: (u32, u32) = (1280, 800);
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct Options {
+    pub script: String,
+    pub out: String,
+    pub view: StandardView,
+    /// A camera aimed as the MCP `screenshot`'s (`--camera JSON`; not with `--view`).
+    pub camera: Option<Aim>,
+    pub size: (u32, u32),
+    /// A section through the mesh (`--section x|y|z[=VALUE]`).
+    pub section: Option<Section>,
+    /// A nodal field contoured on the last solved step (`--field von_mises`).
+    pub field: Option<String>,
+}
+
+/// A view name: a standard view, or the axis looked along (`x`: from the right, `y`: from the
+/// front, `z`: from the top).
+fn view_of(s: &str) -> Option<StandardView> {
+    match s.to_ascii_lowercase().as_str() {
+        "x" => Some(StandardView::Right),
+        "y" => Some(StandardView::Front),
+        "z" => Some(StandardView::Top),
+        other => StandardView::parse(other),
+    }
+}
+
+/// `WxH`, each side 1..=the renderer's limit.
+fn size_of(s: &str) -> Option<(u32, u32)> {
+    let (w, h) = s.split_once(['x', 'X'])?;
+    let (w, h) = (w.trim().parse::<u32>().ok()?, h.trim().parse::<u32>().ok()?);
+    let max = fieldcraft_gpu::capture::MAX_SIDE;
+    ((1..=max).contains(&w) && (1..=max).contains(&h) && u64::from(w) * u64::from(h) <= fieldcraft_gpu::capture::MAX_PIXELS).then_some((w, h))
+}
+
+/// The options: the script, then each flag once, as `--flag value` or `--flag=value`.
+pub fn options(args: &[String]) -> Result<Options, String> {
+    let (mut script, mut out, mut view, mut size, mut section, mut field, mut camera) = (None, None, None, None, None, None, None);
+    let mut it = args.iter();
+    while let Some(arg) = it.next() {
+        if !arg.starts_with("--") {
+            if script.replace(arg.clone()).is_some() {
+                return Err(format!("snapshot takes one script, not `{arg}` too"));
+            }
+            continue;
+        }
+        let (flag, inline) = match arg.split_once('=') {
+            Some((f, v)) => (f, Some(v.to_string())),
+            None => (arg.as_str(), None),
+        };
+        let value = inline.or_else(|| it.next().cloned()).filter(|v| !v.is_empty()).ok_or_else(|| format!("{flag} needs a value"))?;
+        let twice = match flag {
+            "--out" => out.replace(value).is_some(),
+            "--view" => view
+                .replace(
+                    view_of(&value).ok_or_else(|| format!("--view: unknown view `{value}` (iso, x, y, z, front, back, left, right, top, bottom)"))?,
+                )
+                .is_some(),
+            "--size" => size
+                .replace(size_of(&value).ok_or_else(|| {
+                    format!(
+                        "--size: `{value}` is not WxH with each side 1..={} and at most {} pixels",
+                        fieldcraft_gpu::capture::MAX_SIDE,
+                        fieldcraft_gpu::capture::MAX_PIXELS
+                    )
+                })?)
+                .is_some(),
+            "--section" => section
+                .replace(Section::parse(&value).ok_or_else(|| format!("--section: `{value}` is not x, y, z or AXIS=VALUE (x=12.5)"))?)
+                .is_some(),
+            "--field" => field.replace(value).is_some(),
+            "--camera" => {
+                let v: serde_json::Value = serde_json::from_str(&value).map_err(|e| format!("--camera: not JSON: {e}"))?;
+                camera.replace(view::camera(&v).map_err(|e| format!("--camera: {e}"))?).is_some()
+            }
+            other => return Err(format!("snapshot: unknown option `{other}`")),
+        };
+        if twice {
+            return Err(format!("{flag} is given twice"));
+        }
+    }
+    if view.is_some() && camera.is_some() {
+        return Err("give --view or --camera, not both".into());
+    }
+    Ok(Options {
+        script: script.ok_or("snapshot needs a script")?,
+        out: out.ok_or("snapshot needs --out FILE.png")?,
+        view: view.unwrap_or(StandardView::Iso),
+        camera,
+        size: size.unwrap_or(DEFAULT_SIZE),
+        section,
+        field,
+    })
+}
+
+/// The PNG of the session `o` describes, drawn as `policy` says ([`capture::png`]).
+pub fn picture(o: &Options, policy: Policy) -> Result<(Vec<u8>, Renderer, view::Shown), String> {
+    let mut session = crate::session_of(&o.script)?;
+    if let Some(field) = &o.field {
+        session.execute("results.contour", &serde_json::json!({"field": field})).map_err(|e| format!("--field: {e}"))?;
+    }
+    let (w, h) = o.size;
+    let f = match &o.camera {
+        Some(aim) => view::frame_at(&session, aim, w as usize, h as usize, &Palette::LIGHT, o.section).map_err(|e| e.to_string())?,
+        None => view::frame(&session, &Orientation::of(o.view), w as usize, h as usize, &Palette::LIGHT, o.section),
+    };
+    let capturer = Capturer::open(policy);
+    let (png, renderer) = capture::png(&capturer, policy, &f.scene, &[&f.symbols], &f.cam, w, h).map_err(|e| e.to_string())?;
+    Ok((png, renderer, f.shown))
+}
+
+pub fn run(args: &[String]) -> Result<(), String> {
+    let o = options(args)?;
+    let policy = Policy::from_env().map_err(|e| e.to_string())?;
+    let (png, renderer, shown) = picture(&o, policy)?;
+    std::fs::write(&o.out, &png).map_err(|e| format!("{}: {e}", o.out))?;
+    let mut report = crate::picture_report(&renderer, &shown);
+    if let Some(r) = report.as_object_mut() {
+        r.insert("out".into(), o.out.clone().into());
+        r.insert("width".into(), o.size.0.into());
+        r.insert("height".into(), o.size.1.into());
+        match &o.camera {
+            Some(aim) => r.insert("camera".into(), Aim { target: Some(aim.target.clone().unwrap_or(Target::MODEL)), ..aim.clone() }.json()),
+            None => r.insert("view".into(), o.view.label().into()),
+        };
+    }
+    println!("{report}");
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn opts(args: &[&str]) -> Result<Options, String> {
+        options(&args.iter().map(|s| s.to_string()).collect::<Vec<_>>())
+    }
+
+    #[test]
+    fn options_are_checked() {
+        let o = opts(&["s.json", "--out", "a.png"]).unwrap();
+        assert_eq!(
+            o,
+            Options {
+                script: "s.json".into(),
+                out: "a.png".into(),
+                view: StandardView::Iso,
+                camera: None,
+                size: DEFAULT_SIZE,
+                section: None,
+                field: None
+            }
+        );
+        let o = opts(&["s", "--out", "o", "--section", "y=2.5", "--field", "displacement"]).unwrap();
+        assert_eq!((o.section, o.field.as_deref()), (Some(Section { axis: 1, at: Some(2.5) }), Some("displacement")));
+        assert_eq!(opts(&["s", "--out", "o", "--section=Z"]).unwrap().section, Some(Section { axis: 2, at: None }));
+        let o = opts(&["--view=z", "s.json", "--size", "640x480", "--out=b.png"]).unwrap();
+        assert_eq!((o.view, o.size), (StandardView::Top, (640, 480)));
+        assert_eq!(opts(&["s", "--out", "o", "--view", "X"]).unwrap().view, StandardView::Right);
+        assert_eq!(opts(&["s", "--out", "o", "--view", "front"]).unwrap().view, StandardView::Front);
+        let o = opts(&["s", "--out", "o", "--camera", r#"{"yaw": 30, "pitch": 10, "target": [1, 2, 3], "fit": true}"#]).unwrap();
+        assert_eq!(o.camera.and_then(|a| a.target), Some(Target::Point(fieldcraft_render::Vec3::new(1.0, 2.0, 3.0))));
+        for bad in [
+            vec![],
+            vec!["s.json"],
+            vec!["--out", "a.png"],
+            vec!["s", "t", "--out", "o"],
+            vec!["s", "--out"],
+            vec!["s", "--out", "o", "--out", "p"],
+            vec!["s", "--out", "o", "--view", "diagonal"],
+            vec!["s", "--out", "o", "--size", "0x10"],
+            vec!["s", "--out", "o", "--size", "10"],
+            vec!["s", "--out", "o", "--size", "99999x10"],
+            vec!["s", "--out", "o", "--size", "8192x8192"],
+            vec!["s", "--out", "o", "--size", "-5x10"],
+            vec!["s", "--out", "o", "--nope", "1"],
+            vec!["s", "--out", "o", "--section", "w"],
+            vec!["s", "--out", "o", "--section", "x=inf"],
+            vec!["s", "--out", "o", "--section", "x=", "--field", "f"],
+            vec!["s", "--out", "o", "--camera", "{yaw: 1}"],
+            vec!["s", "--out", "o", "--camera", r#"{"yaw": 0}"#],
+            vec!["s", "--out", "o", "--camera", r#"{"yaw": 0, "pitch": 0}"#, "--view", "x"],
+        ] {
+            assert!(opts(&bad).is_err(), "{bad:?}");
+        }
+    }
+
+    /// PNG width, height and pixels (RGBA).
+    fn decode(png: &[u8]) -> (u32, u32, Vec<u8>) {
+        let mut r = png::Decoder::new(std::io::Cursor::new(png)).read_info().unwrap();
+        let mut buf = vec![0; r.output_buffer_size().unwrap()];
+        let info = r.next_frame(&mut buf).unwrap();
+        buf.truncate(info.buffer_size());
+        (info.width, info.height, buf)
+    }
+
+    fn script(dir: &std::path::Path, name: &str, solve: bool) -> String {
+        let mut steps = fieldcraft_engine::sample::cantilever();
+        if solve && let Some(a) = steps.as_array_mut() {
+            a.push(serde_json::json!({"command": "solve.static", "params": {}}));
+        }
+        let path = dir.join(name);
+        std::fs::write(&path, steps.to_string()).unwrap();
+        path.to_string_lossy().into()
+    }
+
+    fn opts_for(script: String) -> Options {
+        Options { script, out: String::new(), view: StandardView::Iso, camera: None, size: (320, 200), section: None, field: None }
+    }
+
+    /// The cantilever drawn headless: a PNG of the size asked for, with the model in it (pixels
+    /// of the hex colour) and its element edges (dark pixels). `auto` draws on the GPU when the
+    /// machine has one and on the CPU otherwise (it must be the GPU under `FIELDCRAFT_REQUIRE_GPU=1`); `cpu` always
+    /// on the CPU, and both pictures show the same model. A section and a field change it.
+    #[test]
+    fn snapshots_the_model_and_its_mesh_headless() {
+        let dir = std::env::temp_dir().join(format!("fieldcraft-snapshot-{}", std::process::id()));
+        std::fs::create_dir_all(&dir).unwrap();
+        let o = opts_for(script(&dir, "cantilever.json", false));
+        for policy in [Policy::Auto, Policy::Cpu] {
+            let (png, drawn, _) = picture(&o, policy).unwrap();
+            let (w, h, px) = decode(&png);
+            assert_eq!((w, h), (320, 200), "{drawn:?}");
+            let hex = Palette::LIGHT.hex;
+            let near = |p: &[u8], c: fieldcraft_render::Rgb, d: u8| p[0].abs_diff(c.0) <= d && p[1].abs_diff(c.1) <= d && p[2].abs_diff(c.2) <= d;
+            // Shaded faces vary in brightness around the hex colour; the edges are near black.
+            let faces = px.chunks(4).filter(|p| near(p, hex, 60) && p[2] > p[0]).count();
+            let edges = px.chunks(4).filter(|p| p[0] < 90 && p[1] < 90 && p[2] < 90).count();
+            assert!(faces > 500, "{drawn:?}: {faces} face pixels");
+            assert!(edges > 100, "{drawn:?}: {edges} edge pixels");
+            if policy == Policy::Cpu {
+                assert_eq!(drawn, Renderer::Cpu { why: None });
+            } else if fieldcraft_gpu::select::gpu_required() {
+                assert!(matches!(drawn, Renderer::Gpu { .. }), "FIELDCRAFT_REQUIRE_GPU=1 but drawn by {drawn:?}");
+            }
+        }
+        // A section along the beam draws half of it.
+        let whole = picture(&o, Policy::Cpu).unwrap().0;
+        let cut = picture(&Options { section: Some(Section { axis: 0, at: None }), ..o.clone() }, Policy::Cpu).unwrap().0;
+        assert_ne!(whole, cut);
+        // A field needs a solved step; on a solved one it is the contour reported.
+        assert!(picture(&Options { field: Some("von_mises".into()), ..o.clone() }, Policy::Cpu).is_err());
+        let solved = Options { field: Some("displacement".into()), ..opts_for(script(&dir, "solved.json", true)) };
+        let (_, _, shown) = picture(&solved, Policy::Auto).unwrap();
+        assert_eq!(shown.contour.map(|c| c.0).as_deref(), Some("displacement"));
+        std::fs::remove_dir_all(&dir).ok();
+    }
+}
@@ -12,7 +12,10 @@ fn cli(host: &str, args: &[&str]) -> std::process::Output {
 #[test]
 fn update_check_reports_the_latest_release() {
    let server = Server::start().unwrap();
-    server.release("latest", &json!({"tag_name": "v99.0.0", "html_url": "https://github.com/jyviko/fieldcraft/releases/tag/v99.0.0", "assets": []}));
+    server.release(
+        "latest",
+        &json!({"tag_name": "v99.0.0", "html_url": "https://github.com/tangency-labs/fieldcraft/releases/tag/v99.0.0", "assets": []}),
+    );
    let out = cli(&server.url(), &["update", "--check"]);
    assert!(out.status.success(), "{out:?}");
    let report: Value = serde_json::from_slice(&out.stdout).unwrap();
@@ -31,4 +31,4 @@ wasm-bindgen-futures = "0.4"
 js-sys = "0.3"
 web-sys = { version = "0.3", features = ["Window", "Document", "Element", "HtmlElement", "HtmlCanvasElement", "HtmlAnchorElement", "Blob", "BlobPropertyBag", "Url", "Location", "DomTokenList", "CssStyleDeclaration", "Event", "EventTarget", "BeforeUnloadEvent", "Storage", "Crypto", "Headers", "Request", "RequestInit", "RequestCache", "Response"] }
 # Autosaves kept in the browser's local storage, which holds text.
-base64 = "0.22"
+base64 = "0.23"
@@ -9,15 +9,15 @@
  <meta property="og:site_name" content="FieldCraft">
  <meta property="og:title" content="FieldCraft">
  <meta property="og:description" content="Open-source CAE built in Rust: structures, heat, fluids, and MCP for AI agents.">
-  <meta property="og:url" content="https://jyviko.github.io/fieldcraft/">
-  <meta property="og:image" content="https://jyviko.github.io/fieldcraft/og.png">
+  <meta property="og:url" content="https://tangency-labs.github.io/fieldcraft/">
+  <meta property="og:image" content="https://tangency-labs.github.io/fieldcraft/og.png">
  <meta property="og:image:width" content="1280">
  <meta property="og:image:height" content="640">
  <meta property="og:image:alt" content="FieldCraft: Open-source CAE built in Rust">
  <meta name="twitter:card" content="summary_large_image">
  <meta name="twitter:title" content="FieldCraft">
  <meta name="twitter:description" content="Open-source CAE built in Rust: structures, heat, fluids, and MCP for AI agents.">
-  <meta name="twitter:image" content="https://jyviko.github.io/fieldcraft/og.png">
+  <meta name="twitter:image" content="https://tangency-labs.github.io/fieldcraft/og.png">
  <link data-trunk rel="rust" data-bin="fieldcraft-web" data-wasm-opt="z" data-weak-refs />
  <link data-trunk rel="icon" type="image/svg+xml" href="../../assets/app-icon/icon-small.svg" />
  <link data-trunk rel="copy-file" href="../../assets/app-icon/icon.iconset/icon_128x128@2x.png" data-target-path="icons" />
@@ -6,8 +6,18 @@ edition.workspace = true
 license.workspace = true
 publish = false

-[lints]
-workspace = true
+# The workspace lints, except unsafe_code: denied, not forbidden, so that src/native_crash.rs
+# (the Windows exception filter, which has no safe API) can allow it. Keep the rest in sync with
+# [workspace.lints].
+[lints.rust]
+unsafe_code = "deny"
+
+[lints.clippy]
+dbg_macro = "warn"
+todo = "warn"
+too_many_arguments = "allow"
+type_complexity = "allow"
+neg_cmp_op_on_partial_ord = "allow"

 [dependencies]
 fieldcraft-engine = { workspace = true }
@@ -23,7 +33,27 @@ log = { workspace = true }
 # operating system's certificates (no bundled root list), and a random install id.
 ureq = { version = "3.4", default-features = false, features = ["rustls-no-provider", "platform-verifier"] }
 rustls = { version = "0.23", default-features = false, features = ["ring", "std"] }
-getrandom = "0.3"
+getrandom = "0.4"
+
+# A termination signal (SIGTERM, SIGINT) closes the window the normal way (terminate.rs).
+[target.'cfg(unix)'.dependencies]
+signal-hook = "0.4"
+
+# The exception filter and minidump of a native crash (src/native_crash.rs).
+[target.'cfg(windows)'.dependencies]
+windows-sys = { version = "0.61", features = [
+    "Win32_Foundation",
+    "Win32_Security",
+    "Win32_Storage_FileSystem",
+    "Win32_System_Diagnostics_Debug",
+    # WriteFile's OVERLAPPED.
+    "Win32_System_IO",
+    "Win32_System_Kernel",
+    "Win32_System_LibraryLoader",
+    # MiniDumpWriteDump.
+    "Win32_System_Memory",
+    "Win32_System_Threading",
+] }

 [build-dependencies]
 # The Windows executable's icon resource (build.rs).
@@ -71,7 +101,7 @@ assets = [
 [package.metadata.generate-rpm]
 name = "fieldcraft"
 license = "MIT OR Apache-2.0"
-url = "https://github.com/jyviko/fieldcraft"
+url = "https://github.com/tangency-labs/fieldcraft"
 assets = [
    { source = "target/release/fieldcraft", dest = "/usr/bin/fieldcraft", mode = "755" },
    { source = "target/release/fieldcraft-cli", dest = "/usr/bin/fieldcraft-cli", mode = "755" },
@@ -115,6 +115,11 @@ fn serve(stream: TcpStream, tx: Sender<ControlRequest>, ctx: egui::Context) {
                }
                ctx.request_repaint();
                let mut r = rrx.recv_timeout(REPLY_TIMEOUT).unwrap_or_else(|_| json!({"ok": false, "error": "timeout"}));
+                // A request waiting for a job (a solve, a mesher): its reply comes when the job
+                // ends, however long it runs; the job always answers, even when cancelled.
+                if r.get(fieldcraft_ui_egui::control::PENDING).is_some() {
+                    r = rrx.recv().unwrap_or_else(|_| json!({"ok": false, "error": "the job ended without a reply"}));
+                }
                if let Some(o) = r.as_object_mut() {
                    o.insert("id".into(), id);
                }
@@ -9,9 +9,12 @@
 //! `fieldcraft_ui_egui::control` and docs/control-protocol.md.
 #![cfg_attr(all(target_os = "windows", not(debug_assertions)), windows_subsystem = "windows")]
 #![deny(clippy::unwrap_used, clippy::expect_used, clippy::panic, clippy::unimplemented, clippy::todo, clippy::unreachable)]
-#![forbid(unsafe_code)]
+// Unsafe code is denied (Cargo.toml): only the Windows exception filter allows it (native_crash.rs).

 mod control_server;
+#[cfg(windows)]
+mod native_crash;
+mod terminate;
 mod update;
 mod usage;

@@ -49,8 +52,8 @@ struct App {
    autosaver: Option<Autosaver>,
    /// App time of the last autosave check.
    autosaved_at: f64,
-    /// The first frame was drawn (the crash journal says the app is up).
-    running: bool,
+    /// Frames drawn so far, up to 2 (the second means the first was presented: the app is up).
+    frames: u8,
    /// Sends the anonymous usage events, when this run may (docs/privacy.md).
    usage: Option<usage::Sender>,
 }
@@ -67,9 +70,13 @@ impl App {

 impl eframe::App for App {
    fn logic(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
-        if !self.running {
-            self.running = true;
-            crash::activity("running");
+        if self.frames < 2 {
+            self.frames += 1;
+            // A second frame right away, which means the first was presented: the app is up.
+            ctx.request_repaint();
+            if self.frames == 2 {
+                crash::phase(crash::RUNNING);
+            }
        }
        self.app.logic(ctx);
        if self.app.now - self.autosaved_at >= AUTOSAVE_SECONDS {
@@ -162,10 +169,18 @@ fn start_reporting() -> Vec<crash::Summary> {
        b.version_line(),
        crash::default_dir().map(|d| d.display().to_string()).unwrap_or_default()
    );
-    crash::activity("startup");
    crashed
 }

+/// egui-wgpu is about to start a step of getting the graphics device and the window's surface
+/// up: the crash journal keeps it, and the adapter once it is picked (#299).
+fn startup_step(step: &'static str, detail: &str) {
+    if step == eframe::egui_wgpu::STEP_ADAPTER_CHOSEN {
+        crash::set_environment(&format!("Renderer: {detail}"));
+    }
+    crash::phase(step);
+}
+
 /// Command-line options.
 #[derive(Debug, Default, PartialEq)]
 struct Args {
@@ -223,6 +238,12 @@ fn main() -> eframe::Result {
        fieldcraft_io::recovery::use_automation_dir();
    }
    let crashed = start_reporting();
+    // A crash in native code (a graphics driver) says where it happened: the exception and the
+    // module on Windows, and on every system the startup step the app was in.
+    #[cfg(windows)]
+    native_crash::install();
+    eframe::egui_wgpu::set_startup_hook(startup_step);
+    crash::phase("window");
    let options = eframe::NativeOptions {
        viewport: egui::ViewportBuilder::default()
            .with_title("FieldCraft")
@@ -245,6 +266,7 @@ fn main() -> eframe::Result {
        "FieldCraft",
        options,
        Box::new(move |cc| {
+            crash::phase("app setup");
            let mut session = Session::default();
            // The window's model: its commands go into the crash journal.
            session.crash_journal = crash::enabled();
@@ -265,7 +287,21 @@ fn main() -> eframe::Result {
            if let Some(rs) = &cc.wgpu_render_state {
                let info = rs.adapter.get_info();
                log::info!("graphics {:?} {} ({}), MSAA {}x (requested {MSAA}x)", info.backend, info.name, info.driver, rs.msaa_samples);
+                crash::set_environment(&format!("Renderer: {:?} {} ({}), MSAA {}x", info.backend, info.name, info.driver, rs.msaa_samples));
+                crash::phase("viewport pipelines (shader compile)");
                app.set_wgpu(rs, DEPTH_BITS, rs.msaa_samples, &cc.egui_ctx);
+                // The graphics driver is loaded now; it may have put its own exception filter
+                // in front of ours.
+                #[cfg(windows)]
+                native_crash::reinstall();
+            }
+            // `kill` or Ctrl-C closes the window as Close does: autosaved, no crash (#248).
+            let ctx = cc.egui_ctx.clone();
+            if let Err(e) = terminate::watch(move || {
+                ctx.send_viewport_cmd(egui::ViewportCommand::Close);
+                ctx.request_repaint();
+            }) {
+                log::warn!("termination signals: {e}");
            }
            if let Some(port) = args.control {
                app = app.with_control(control_server::start(port, cc.egui_ctx.clone()));
@@ -285,7 +321,8 @@ fn main() -> eframe::Result {
                Autosaver::new(&dir).map_err(|e| log::warn!("autosave unavailable: {e}")).ok()
            });
            app.announce_crashes(&crashed);
-            Ok(Box::new(App { app, autosaver, autosaved_at: 0.0, running: false, usage }))
+            crash::phase("first frame");
+            Ok(Box::new(App { app, autosaver, autosaved_at: 0.0, frames: 0, usage }))
        }),
    )
 }
@@ -0,0 +1,290 @@
+//! Windows: what a crash in native code leaves behind (docs/crash-reports.md, #299).
+//!
+//! A crash inside a graphics driver or another DLL (an access violation, a stack overflow) is no
+//! Rust panic: the panic hook never runs and the next start only found "an unclean exit". An
+//! unhandled-exception filter now writes, before the process goes, a small JSON file with the
+//! exception code, the faulting module and the offset into it, and a minidump, next to the run's
+//! crash journal (`fieldcraft_engine::crash::native_paths`). The next start puts both into the
+//! unclean exit's report, with the startup step the journal says the app was in. Everything that
+//! can be tested without Windows (reading the file, the report, the startup steps) lives in
+//! `fieldcraft_engine::crash` and is tested there.
+//!
+//! Installing an exception filter and asking the system which module holds an address have no
+//! safe API, hence the `unsafe_code` allowance on this module, the only one in FieldCraft (the
+//! app crate denies unsafe code instead of forbidding it for this). The filter runs on a thread
+//! that may have a broken heap or almost no stack left: it doesn't allocate, formats into a buffer
+//! on the stack, and skips the minidump after a stack overflow.
+//!
+//! Adapted from SolidCraft's `apps/solidcraft/src/native_crash.rs` (MIT OR Apache-2.0), see
+//! ATTRIBUTION.md.
+#![allow(unsafe_code)]
+
+use std::fmt::Write as _;
+use std::os::windows::ffi::OsStrExt;
+use std::path::Path;
+use std::sync::OnceLock;
+use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
+
+use windows_sys::Win32::Foundation::{CloseHandle, GENERIC_WRITE, HANDLE, HMODULE, INVALID_HANDLE_VALUE};
+use windows_sys::Win32::Storage::FileSystem::{CREATE_ALWAYS, CreateFileW, FILE_ATTRIBUTE_NORMAL, WriteFile};
+use windows_sys::Win32::System::Diagnostics::Debug::{
+    EXCEPTION_CONTINUE_SEARCH, EXCEPTION_POINTERS, MINIDUMP_EXCEPTION_INFORMATION, MiniDumpNormal, MiniDumpWithThreadInfo,
+    MiniDumpWithUnloadedModules, MiniDumpWriteDump, SetUnhandledExceptionFilter,
+};
+use windows_sys::Win32::System::LibraryLoader::{
+    GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS, GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT, GetModuleFileNameW, GetModuleHandleExW,
+};
+use windows_sys::Win32::System::Threading::{GetCurrentProcess, GetCurrentProcessId, GetCurrentThreadId};
+
+/// Where the filter writes (NUL-terminated UTF-16), set once by [`install`].
+struct Paths {
+    info: Vec<u16>,
+    dump: Vec<u16>,
+}
+
+static PATHS: OnceLock<Paths> = OnceLock::new();
+/// The filter that was installed before ours (called after ours), as an address.
+static PREVIOUS: AtomicUsize = AtomicUsize::new(0);
+/// The filter has started writing (a second exception while it does is left alone).
+static BUSY: AtomicBool = AtomicBool::new(false);
+
+const STATUS_ACCESS_VIOLATION: u32 = 0xC000_0005;
+const STATUS_IN_PAGE_ERROR: u32 = 0xC000_0006;
+const STATUS_STACK_OVERFLOW: u32 = 0xC000_00FD;
+
+/// Catch native crashes from now on (after `fieldcraft_engine::crash::install`; nothing without it).
+pub fn install() {
+    let Some((info, dump)) = fieldcraft_engine::crash::native_paths() else { return };
+    let wide = |p: &Path| p.as_os_str().encode_wide().chain([0]).collect::<Vec<u16>>();
+    if PATHS.set(Paths { info: wide(&info), dump: wide(&dump) }).is_ok() {
+        set_filter();
+    }
+}
+
+/// Put the filter back on top: a DLL loaded since (a graphics driver) may have set its own,
+/// which is then called after ours.
+pub fn reinstall() {
+    if PATHS.get().is_some() {
+        set_filter();
+    }
+}
+
+fn set_filter() {
+    // SAFETY: `filter` has the signature the system calls it with and stays valid for the
+    // process's life.
+    let previous = unsafe { SetUnhandledExceptionFilter(Some(filter)) };
+    if let Some(p) = previous
+        && p as usize != filter as *const () as usize
+    {
+        PREVIOUS.store(p as usize, Ordering::SeqCst);
+    }
+}
+
+/// The unhandled-exception filter: record, then let the previous filter (or the system) go on.
+unsafe extern "system" fn filter(pointers: *const EXCEPTION_POINTERS) -> i32 {
+    if !BUSY.swap(true, Ordering::SeqCst) {
+        // SAFETY: the system passes valid exception pointers for the duration of the call.
+        unsafe { record(pointers) };
+    }
+    let previous = PREVIOUS.load(Ordering::SeqCst);
+    if previous != 0 && previous != filter as *const () as usize {
+        // SAFETY: the address came from `SetUnhandledExceptionFilter` as a filter of this type.
+        let previous: unsafe extern "system" fn(*const EXCEPTION_POINTERS) -> i32 = unsafe { std::mem::transmute(previous) };
+        // SAFETY: as for this filter.
+        return unsafe { previous(pointers) };
+    }
+    EXCEPTION_CONTINUE_SEARCH
+}
+
+/// A fixed buffer to format into without allocating (what doesn't fit is cut off).
+struct Buf {
+    bytes: [u8; 2048],
+    len: usize,
+}
+
+impl std::fmt::Write for Buf {
+    fn write_str(&mut self, s: &str) -> std::fmt::Result {
+        let room = self.bytes.len().saturating_sub(self.len);
+        let n = s.len().min(room);
+        if let (Some(to), Some(from)) = (self.bytes.get_mut(self.len..self.len + n), s.as_bytes().get(..n)) {
+            to.copy_from_slice(from);
+            self.len += n;
+        }
+        Ok(())
+    }
+}
+
+/// The usual names of the exception codes a crash shows.
+fn code_name(code: u32) -> &'static str {
+    match code {
+        STATUS_ACCESS_VIOLATION => "EXCEPTION_ACCESS_VIOLATION",
+        STATUS_IN_PAGE_ERROR => "EXCEPTION_IN_PAGE_ERROR",
+        STATUS_STACK_OVERFLOW => "EXCEPTION_STACK_OVERFLOW",
+        0xC000_001D => "EXCEPTION_ILLEGAL_INSTRUCTION",
+        0xC000_0094 => "EXCEPTION_INT_DIVIDE_BY_ZERO",
+        0xC000_0096 => "EXCEPTION_PRIV_INSTRUCTION",
+        0xC000_008C => "EXCEPTION_ARRAY_BOUNDS_EXCEEDED",
+        0xC000_0374 => "STATUS_HEAP_CORRUPTION",
+        0xC000_0409 => "STATUS_STACK_BUFFER_OVERRUN",
+        0xC000_0602 => "STATUS_FAIL_FAST_EXCEPTION",
+        0x8000_0003 => "EXCEPTION_BREAKPOINT",
+        0xE06D_7363 => "C++ exception",
+        _ => "exception",
+    }
+}
+
+/// Write what `pointers` says into the info file, then the minidump.
+unsafe fn record(pointers: *const EXCEPTION_POINTERS) {
+    let Some(paths) = PATHS.get() else { return };
+    if pointers.is_null() {
+        return;
+    }
+    // SAFETY: checked non-null; the system keeps it valid during the filter.
+    let rec = unsafe { (*pointers).ExceptionRecord };
+    if rec.is_null() {
+        return;
+    }
+    // SAFETY: as above.
+    let rec = unsafe { &*rec };
+    let code = rec.ExceptionCode as u32;
+    let address = rec.ExceptionAddress as usize;
+    let mut module: HMODULE = std::ptr::null_mut();
+    let mut name = [0u16; 512];
+    // SAFETY: FROM_ADDRESS takes the address in place of a name; UNCHANGED_REFCOUNT means no
+    // handle to release; `name` is as long as we say.
+    let len = unsafe {
+        if GetModuleHandleExW(
+            GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS | GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT,
+            address as *const u16,
+            &mut module,
+        ) != 0
+        {
+            GetModuleFileNameW(module, name.as_mut_ptr(), name.len() as u32) as usize
+        } else {
+            0
+        }
+    };
+    // SAFETY: no preconditions.
+    let thread = unsafe { GetCurrentThreadId() };
+    let mut b = Buf { bytes: [0; 2048], len: 0 };
+    let _ = write!(b, "{{\"code\":\"0x{code:08X}\",\"name\":\"{}\",\"address\":\"0x{address:016X}\",\"thread\":{thread}", code_name(code));
+    if len > 0 {
+        let _ = write!(b, ",\"offset\":\"0x{:X}\",\"module\":\"", address.wrapping_sub(module as usize));
+        for c in char::decode_utf16(name.iter().take(len).copied()) {
+            let _ = match c.unwrap_or(char::REPLACEMENT_CHARACTER) {
+                '"' => b.write_str("\\\""),
+                '\\' => b.write_str("\\\\"),
+                c if (c as u32) < 0x20 => b.write_str("?"),
+                c => b.write_char(c),
+            };
+        }
+        let _ = b.write_str("\"");
+    }
+    if matches!(code, STATUS_ACCESS_VIOLATION | STATUS_IN_PAGE_ERROR) && rec.NumberParameters >= 2 {
+        let what = match rec.ExceptionInformation[0] {
+            0 => "read of",
+            1 => "write to",
+            8 => "execution at",
+            _ => "access to",
+        };
+        let _ = write!(b, ",\"detail\":\"{what} 0x{:016X}\"", rec.ExceptionInformation[1]);
+    }
+    let _ = b.write_str("}");
+    let bytes = b.bytes.get(..b.len).unwrap_or_default();
+    // SAFETY: NUL-terminated path; the handle is closed below.
+    unsafe {
+        let file = create(&paths.info);
+        if !file.is_null() {
+            let mut written = 0u32;
+            WriteFile(file, bytes.as_ptr(), bytes.len() as u32, &mut written, std::ptr::null_mut());
+            CloseHandle(file);
+        }
+    }
+    // After a stack overflow there is no stack left for writing a minidump.
+    if code == STATUS_STACK_OVERFLOW {
+        return;
+    }
+    // SAFETY: as above; the exception information points at this thread's exception.
+    unsafe {
+        let file = create(&paths.dump);
+        if !file.is_null() {
+            let exception = MINIDUMP_EXCEPTION_INFORMATION { ThreadId: thread, ExceptionPointers: pointers as *mut _, ClientPointers: 0 };
+            MiniDumpWriteDump(
+                GetCurrentProcess(),
+                GetCurrentProcessId(),
+                file,
+                MiniDumpNormal | MiniDumpWithThreadInfo | MiniDumpWithUnloadedModules,
+                &exception,
+                std::ptr::null(),
+                std::ptr::null(),
+            );
+            CloseHandle(file);
+        }
+    }
+}
+
+/// A new file at `path` (NUL-terminated) for writing, or null.
+unsafe fn create(path: &[u16]) -> HANDLE {
+    // SAFETY: the caller passes a NUL-terminated path.
+    let h = unsafe { CreateFileW(path.as_ptr(), GENERIC_WRITE, 0, std::ptr::null(), CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, std::ptr::null_mut()) };
+    if h == INVALID_HANDLE_VALUE { std::ptr::null_mut() } else { h }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::path::PathBuf;
+
+    /// The child half: install crash reporting and the filter, then fault in native code.
+    #[test]
+    fn child() {
+        let Some(dir) = std::env::var_os("FIELDCRAFT_NATIVE_CRASH_CHILD") else { return };
+        let build = fieldcraft_engine::crash::Build { version: "9.9.9", commit: "abc1234" };
+        let fresh = fieldcraft_engine::crash::install(PathBuf::from(dir), build);
+        println!("FRESH {}", serde_json::to_string(&fresh).unwrap_or_default());
+        if std::env::var_os("FIELDCRAFT_NATIVE_CRASH_FAULT").is_none() {
+            fieldcraft_engine::crash::end_session();
+            return;
+        }
+        super::install();
+        fieldcraft_engine::crash::phase("device creation");
+        // SAFETY: none; this is the crash under test (a read of address 16, as a null struct
+        // pointer's field would be).
+        let v = unsafe { std::ptr::read_volatile(16 as *const u64) };
+        println!("unreachable {v}");
+    }
+
+    fn run(dir: &std::path::Path, fault: bool) -> std::process::Output {
+        let mut c = std::process::Command::new(std::env::current_exe().unwrap());
+        c.args(["--exact", "native_crash::tests::child", "--test-threads=1", "--nocapture"]).env("FIELDCRAFT_NATIVE_CRASH_CHILD", dir);
+        if fault {
+            c.env("FIELDCRAFT_NATIVE_CRASH_FAULT", "1");
+        }
+        c.output().unwrap()
+    }
+
+    #[test]
+    fn an_access_violation_is_reported_with_its_module_step_and_minidump() {
+        let dir = std::env::temp_dir().join(format!("fieldcraft-native-crash-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&dir);
+        let out = run(&dir, true);
+        assert_eq!(out.status.code().map(|c| c as u32), Some(super::STATUS_ACCESS_VIOLATION), "{out:?}");
+        let sessions: Vec<PathBuf> = std::fs::read_dir(dir.join("sessions")).unwrap().flatten().map(|e| e.path()).collect();
+        let info = sessions.iter().find(|p| p.to_string_lossy().ends_with(".native.json")).expect("the filter wrote what it caught");
+        let v: serde_json::Value = serde_json::from_slice(&std::fs::read(info).unwrap()).unwrap();
+        assert_eq!(v["code"], "0xC0000005", "{v}");
+        assert_eq!(v["detail"], "read of 0x0000000000000010", "{v}");
+        assert!(v["module"].as_str().unwrap().to_lowercase().contains("fieldcraft"), "the fault is in the test binary: {v}");
+        let dump = sessions.iter().find(|p| p.extension().is_some_and(|e| e == "dmp")).expect("a minidump");
+        assert_eq!(std::fs::read(dump).unwrap().get(..4), Some(&b"MDMP"[..]));
+        // The next start reports it.
+        let out = run(&dir, false);
+        assert!(out.status.success(), "{out:?}");
+        let reports = fieldcraft_engine::crash::list(&dir);
+        assert_eq!(reports.len(), 1, "{reports:?}");
+        let r = fieldcraft_engine::crash::read(&dir, &reports[0].id).unwrap();
+        assert!(r["message"].as_str().unwrap().contains("EXCEPTION_ACCESS_VIOLATION (0xC0000005) in fieldcraft"), "{r}");
+        assert!(r["message"].as_str().unwrap().contains("during startup (device creation"), "{r}");
+        assert!(r.get("minidump_path").is_some(), "{r}");
+        let _ = std::fs::remove_dir_all(&dir);
+    }
+}
@@ -0,0 +1,143 @@
+//! A request to terminate (SIGTERM, SIGINT on Unix) closes the window the normal way.
+//!
+//! Without this, `kill PID`, Ctrl-C in the terminal, a system shutdown or a test harness's timeout
+//! ended the process on the spot: no `on_exit`, so no last autosave and no clean end of the crash
+//! journal, and the next start filed an `unclean_exit` crash report for what was no crash (#248:
+//! "ended without a clean exit between commands (last: control ui.capture)" was an automation run
+//! stopped with SIGTERM after its capture). Now the first signal asks the window to close, which
+//! autosaves, ends the journal and exits as a click on Close does; the journal notes the signal,
+//! so a run that still dies while closing says why. A second signal, for a window that does not
+//! close, ends the process at once with the signal's default action.
+//!
+//! SIGHUP is left alone: `nohup fieldcraft &` ignores it on purpose so the app outlives its
+//! terminal, and a handler would override that (a safe API cannot ask whether a signal was
+//! ignored at launch).
+//!
+//! Windows has no such signals: a window there is closed through its messages, which eframe
+//! already turns into a normal close.
+
+use std::io;
+
+/// The signals that ask the app to terminate.
+#[cfg(unix)]
+const SIGNALS: [i32; 2] = [signal_hook::consts::SIGTERM, signal_hook::consts::SIGINT];
+
+/// The signal's usual name, for the log and the crash journal.
+#[cfg(unix)]
+fn name(signal: i32) -> &'static str {
+    match signal {
+        signal_hook::consts::SIGTERM => "SIGTERM",
+        signal_hook::consts::SIGINT => "SIGINT",
+        _ => "signal",
+    }
+}
+
+/// Call `close` (on a thread of its own) on the first termination signal; a second one ends the
+/// process with the signal's default action.
+#[cfg(unix)]
+pub fn watch(close: impl Fn() + Send + 'static) -> io::Result<()> {
+    let mut signals = signal_hook::iterator::Signals::new(SIGNALS)?;
+    std::thread::Builder::new().name("terminate".into()).spawn(move || {
+        let mut asked = false;
+        for signal in signals.forever() {
+            if asked {
+                log::warn!("{}: the window did not close; ending now", name(signal));
+                if let Err(e) = signal_hook::low_level::emulate_default_handler(signal) {
+                    log::error!("{}: {e}", name(signal));
+                    std::process::exit(128 + signal);
+                }
+                continue;
+            }
+            asked = true;
+            log::info!("{}: closing", name(signal));
+            fieldcraft_engine::crash::activity(&format!("terminating ({})", name(signal)));
+            close();
+        }
+    })?;
+    Ok(())
+}
+
+/// Nothing to watch without Unix signals.
+#[cfg(not(unix))]
+pub fn watch(_close: impl Fn() + Send + 'static) -> io::Result<()> {
+    Ok(())
+}
+
+#[cfg(all(test, unix))]
+mod tests {
+    use std::path::{Path, PathBuf};
+    use std::sync::mpsc;
+
+    use fieldcraft_engine::crash;
+
+    /// The child half: start crash reporting as the app does, then get SIGTERM. With the watcher
+    /// the "window" (here the main thread) closes the normal way; without it the process dies.
+    #[test]
+    fn child() {
+        let Some(dir) = std::env::var_os("FIELDCRAFT_TERMINATE_CHILD") else { return };
+        let build = crash::Build { version: "9.9.9", commit: "abc1234" };
+        let fresh = crash::install(PathBuf::from(dir), build);
+        if std::env::var_os("FIELDCRAFT_TERMINATE_NEXT").is_some() {
+            // The next start: what it reports of the run before.
+            println!("FRESH {}", fresh.iter().map(|s| s.message.as_str()).collect::<Vec<_>>().join(" | "));
+            crash::end_session();
+            return;
+        }
+        crash::activity("control ui.capture");
+        if std::env::var_os("FIELDCRAFT_TERMINATE_WATCH").is_some() {
+            let (tx, rx) = mpsc::channel();
+            super::watch(move || {
+                let _ = tx.send(());
+            })
+            .unwrap();
+            signal_hook::low_level::raise(signal_hook::consts::SIGTERM).unwrap();
+            // What `on_exit` does once the window has closed.
+            rx.recv().unwrap();
+            crash::end_session();
+            println!("CLOSED");
+            return;
+        }
+        signal_hook::low_level::raise(signal_hook::consts::SIGTERM).unwrap();
+        // Not reached: SIGTERM's default action ends the process.
+        std::thread::sleep(std::time::Duration::from_secs(10));
+    }
+
+    #[test]
+    fn sigterm_closes_cleanly_and_leaves_no_crash_report() {
+        let root = std::env::temp_dir().join(format!("fieldcraft-terminate-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&root);
+        let run = |dir: &Path, mode: &str| {
+            let mut c = std::process::Command::new(std::env::current_exe().unwrap());
+            c.args(["--exact", "terminate::tests::child", "--test-threads=1", "--nocapture"]).env("FIELDCRAFT_TERMINATE_CHILD", dir);
+            match mode {
+                "watch" => c.env("FIELDCRAFT_TERMINATE_WATCH", "1"),
+                "next" => c.env("FIELDCRAFT_TERMINATE_NEXT", "1"),
+                _ => &mut c,
+            };
+            c.output().unwrap()
+        };
+        // What the next start in `dir` reports of the run before.
+        let reported_at_next_start = |dir: &Path| {
+            let out = run(dir, "next");
+            assert!(out.status.success(), "{out:?}");
+            let stdout = String::from_utf8_lossy(&out.stdout).to_string();
+            stdout.lines().find_map(|l| l.split_once("FRESH ").map(|(_, r)| r.trim().to_string())).unwrap_or_else(|| panic!("{stdout}"))
+        };
+
+        // Without the watcher (the bug): killed, and the journal it leaves reads as a crash.
+        let unwatched = root.join("unwatched");
+        let out = run(&unwatched, "kill");
+        use std::os::unix::process::ExitStatusExt;
+        assert_eq!(out.status.signal(), Some(signal_hook::consts::SIGTERM), "{out:?}");
+        let reported = reported_at_next_start(&unwatched);
+        assert!(reported.contains("ended without a clean exit") && reported.contains("control ui.capture"), "{reported}");
+
+        // With it: the close runs, the journal ends, and nothing is reported as a crash.
+        let watched = root.join("watched");
+        let out = run(&watched, "watch");
+        assert!(out.status.success(), "{out:?}");
+        assert!(String::from_utf8_lossy(&out.stdout).contains("CLOSED"), "{out:?}");
+        assert_eq!(reported_at_next_start(&watched), "");
+        let _ = std::fs::remove_dir_all(&root);
+    }
+}
@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="24" height="24" viewBox="0 0 24 24">
+  <title>geometry.check</title>
+  <g id="Layer_1" data-name="Layer 1">
+    <path d="M9 3 L16 6.5 L16 13 L9 16.5 L2 13 L2 6.5 Z" fill="#2d4e70" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M2 6.5 L9 10 L16 6.5 M9 10 L9 16.5" fill="none" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M2 6.5 L2 9.5" fill="none" stroke="#f0b44a" stroke-width="2.25" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M13.5 17 C13.5 15.067 15.067 13.5 17 13.5 C18.933 13.5 20.5 15.067 20.5 17 C20.5 18.933 18.933 20.5 17 20.5 C15.067 20.5 13.5 18.933 13.5 17 Z" fill="none" stroke="#4f9ce8" stroke-width="1.75" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M19.5 19.5 L22 22" fill="none" stroke="#4f9ce8" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"/>
+  </g>
+</svg>
@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="24" height="24" viewBox="0 0 24 24">
+  <title>geometry.face.absorb</title>
+  <g id="Layer_1" data-name="Layer 1">
+    <path d="M3 8 L12 4 L21 8 L12 12 Z" fill="#2d4e70" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M3 8 L3 16 L12 20 L12 12 M12 20 L21 16 L21 8" fill="none" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M14.5 5.1 L17 6.2 L8 10.3 L5.5 9.2 Z" fill="#f0b44a" stroke="#f0b44a" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M3 8 L12 4 L21 8 L12 12 Z" fill="none" stroke="#4f9ce8" stroke-width="1.75" stroke-linecap="round" stroke-linejoin="round"/>
+  </g>
+</svg>
@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="24" height="24" viewBox="0 0 24 24">
+  <title>geometry.face.split</title>
+  <g id="Layer_1" data-name="Layer 1">
+    <path d="M3 8 L12 4 L21 8 L12 12 Z" fill="#2d4e70" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M3 8 L3 16 L12 20 L12 12 M12 20 L21 16 L21 8" fill="none" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M7.5 10 L16.5 6" fill="none" stroke="#f0b44a" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M5 4.5 L9 2.5 M15 9.5 L19 7.5" fill="none" stroke="#4f9ce8" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round" stroke-dasharray="1.5 1.5"/>
+  </g>
+</svg>
@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="24" height="24" viewBox="0 0 24 24">
+  <title>geometry.faces.merge</title>
+  <g id="Layer_1" data-name="Layer 1">
+    <path d="M3 8 L12 4 L21 8 L12 12 Z" fill="#2d4e70" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M3 8 L3 16 L12 20 L12 12 M12 20 L21 16 L21 8" fill="none" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M7.5 6 L16.5 10" fill="none" stroke="#f0b44a" stroke-width="1.25" stroke-linecap="round" stroke-linejoin="round" stroke-dasharray="1.5 2"/>
+    <path d="M3 8 L12 4 L21 8 L12 12 Z" fill="none" stroke="#4f9ce8" stroke-width="1.75" stroke-linecap="round" stroke-linejoin="round"/>
+  </g>
+</svg>
@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="24" height="24" viewBox="0 0 24 24">
+  <title>geometry.stitch</title>
+  <g id="Layer_1" data-name="Layer 1">
+    <path d="M3 6 L10.5 6 L10.5 18 L3 18 Z" fill="#2d4e70" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M13.5 6 L21 6 L21 18 L13.5 18 Z" fill="#2d4e70" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M9 8.5 L15 8.5" fill="none" stroke="#f0b44a" stroke-width="1.75" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M9 12 L15 12" fill="none" stroke="#f0b44a" stroke-width="1.75" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M9 15.5 L15 15.5" fill="none" stroke="#f0b44a" stroke-width="1.75" stroke-linecap="round" stroke-linejoin="round"/>
+  </g>
+</svg>
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="24" height="24" viewBox="0 0 24 24">
+  <title>mesh.block</title>
+  <g id="Layer_1" data-name="Layer 1">
+    <path d="M4 6 L16 3 L20 15 L8 19 Z" fill="#2d4e70" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M8 5 L12.33 16.33 M12 4 L16.67 17.67 M5.33 10.33 L17.33 7 M6.67 14.67 L18.67 11" fill="none" stroke="#4f9ce8" stroke-linecap="round" stroke-linejoin="round"/>
+  </g>
+</svg>
@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="24" height="24" viewBox="0 0 24 24">
+  <title>mesh.export.stl</title>
+  <g id="Layer_1" data-name="Layer 1">
+    <path d="M3 9 L9 5 L15 9 L9 13 Z" fill="#2d4e70" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M3 9 L3 17 L9 21 L9 13 M9 21 L15 17 L15 9" fill="none" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M3 9 L9 21 M9 13 L15 17" fill="none" stroke="#dde2ea" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M15 15 L21 15 M18.19 16.53 L21 15 L18.19 13.47" fill="none" stroke="#4f9ce8" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+  </g>
+</svg>
@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="24" height="24" viewBox="0 0 24 24">
+  <title>mesh.hex.extrude</title>
+  <g id="Layer_1" data-name="Layer 1">
+    <path d="M6 20 L18 20 L18 11.6 C14 9.467 10 9.467 6 11.6 Z" fill="#2d4e70" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M6 17.2 L18 17.2 M6 14.4 C10 12.8 14 12.8 18 14.4 M10 20 L10 9.9 M14 20 L14 9.9" fill="none" stroke="#4f9ce8" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M3 9.2 C9 5.333 15 5.333 21 9.2" fill="none" stroke="#4f9ce8" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M12 6 L12 3 M10.5 4.5 L12 3 L13.5 4.5" fill="none" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+  </g>
+</svg>
@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="24" height="24" viewBox="0 0 24 24">
+  <title>mesh.mirror</title>
+  <g id="Layer_1" data-name="Layer 1">
+    <path d="M12 2 L12 22" fill="none" stroke="#4f9ce8" stroke-width="1.25" stroke-linecap="round" stroke-linejoin="round" stroke-dasharray="2 1.5"/>
+    <path d="M10 5 L3 7 L3 17 L10 19 Z" fill="#2d4e70" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M3 12 L10 12 M6.5 6 L6.5 18" fill="none" stroke="#dde2ea" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M14 5 L21 7 L21 17 L14 19 Z" fill="#2d4e70" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M14 12 L21 12 M17.5 6 L17.5 18" fill="none" stroke="#dde2ea" stroke-linecap="round" stroke-linejoin="round"/>
+  </g>
+</svg>
@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="24" height="24" viewBox="0 0 24 24">
+  <title>mesh.node.relax</title>
+  <g id="Layer_1" data-name="Layer 1">
+    <path d="M3 12 C3 7.029 7.029 3 12 3 C16.971 3 21 7.029 21 12 C21 16.971 16.971 21 12 21 C7.029 21 3 16.971 3 12 Z" fill="none" stroke="#dde2ea" stroke-width="1.25" stroke-linecap="round" stroke-linejoin="round" stroke-dasharray="2 2"/>
+    <path d="M5 12 L19 12 M12 5 L12 19" fill="none" stroke="#dde2ea" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M7.5 8 L16.5 8 M7.5 16 L16.5 16 M8 7.5 L8 16.5 M16 7.5 L16 16.5" fill="none" stroke="#dde2ea" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M9.6 12 C9.6 10.675 10.675 9.6 12 9.6 C13.325 9.6 14.4 10.675 14.4 12 C14.4 13.325 13.325 14.4 12 14.4 C10.675 14.4 9.6 13.325 9.6 12 Z" fill="#4f9ce8" stroke="#4f9ce8" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+  </g>
+</svg>
@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="24" height="24" viewBox="0 0 24 24">
+  <title>mesh.plan</title>
+  <g id="Layer_1" data-name="Layer 1">
+    <path d="M12 3 L20 7 L20 16 L12 20 L4 16 L4 7 Z" fill="#2d4e70" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M4 7 L12 11 L20 7 M12 11 L12 20" fill="none" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M4 11.5 L12 15.5 L20 11.5 M8 9 L8 18 M16 9 L16 18" fill="none" stroke="#4f9ce8" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M12 3 L12 5.4 M20 7 L15.2 7 M12 11 L12 8.6 M4 7 L8.8 7" fill="none" stroke="#4f9ce8" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M8.8 7 C8.8 7.884 10.233 8.6 12 8.6 C13.767 8.6 15.2 7.884 15.2 7 C15.2 6.116 13.767 5.4 12 5.4 C10.233 5.4 8.8 6.116 8.8 7 Z" fill="none" stroke="#f0b44a" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+  </g>
+</svg>
@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="24" height="24" viewBox="0 0 24 24">
+  <title>mesh.quality.mark</title>
+  <g id="Layer_1" data-name="Layer 1">
+    <path d="M3 3 L11 3 L11 11 L3 11 Z" fill="#2d4e70" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M13 3 L21 3 L21 11 L13 11 Z" fill="#2d4e70" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M3 13 L11 13 L11 21 L3 21 Z" fill="#2d4e70" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M13 14 L21 13 L20 21 L14 19 Z" fill="#f0b44a" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+  </g>
+</svg>
@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="24" height="24" viewBox="0 0 24 24">
+  <title>results.export.vtu</title>
+  <g id="Layer_1" data-name="Layer 1">
+    <path d="M4 3 L12 3 L16 7 L16 21 L4 21 Z" fill="#2d4e70" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M12 3 L12 7 L16 7" fill="none" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M7 17 L7 14 M10 17 L10 11 M13 17 L13 13" fill="none" stroke="#4f9ce8" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M15 15 L21 15 M18.19 16.53 L21 15 L18.19 13.47" fill="none" stroke="#4f9ce8" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+  </g>
+</svg>
@@ -0,0 +1 @@
+{"shapes": [{"d": "M9 3 L16 6.5 L16 13 L9 16.5 L2 13 L2 6.5 Z", "fill": "soft", "stroke": "line"}, {"d": "M2 6.5 L9 10 L16 6.5 M9 10 L9 16.5", "stroke": "line"}, {"line": [2, 6.5, 2, 9.5], "stroke": "warm", "width": 2.25}, {"circle": [17, 17, 3.5], "stroke": "accent", "width": 1.75}, {"line": [19.5, 19.5, 22, 22], "stroke": "accent", "width": 2}]}
@@ -0,0 +1 @@
+{"shapes": [{"d": "M3 8 L12 4 L21 8 L12 12 Z", "fill": "soft", "stroke": "line"}, {"d": "M3 8 L3 16 L12 20 L12 12 M12 20 L21 16 L21 8", "stroke": "line"}, {"d": "M14.5 5.1 L17 6.2 L8 10.3 L5.5 9.2 Z", "fill": "warm", "stroke": "warm", "width": 1}, {"d": "M3 8 L12 4 L21 8 L12 12 Z", "stroke": "accent", "width": 1.75}]}
@@ -0,0 +1 @@
+{"shapes": [{"d": "M3 8 L12 4 L21 8 L12 12 Z", "fill": "soft", "stroke": "line"}, {"d": "M3 8 L3 16 L12 20 L12 12 M12 20 L21 16 L21 8", "stroke": "line"}, {"line": [7.5, 10, 16.5, 6], "stroke": "warm", "width": 2}, {"d": "M5 4.5 L9 2.5 M15 9.5 L19 7.5", "stroke": "accent", "width": 1.5, "dash": [1.5, 1.5]}]}
@@ -0,0 +1 @@
+{"shapes": [{"d": "M3 8 L12 4 L21 8 L12 12 Z", "fill": "soft", "stroke": "line"}, {"d": "M3 8 L3 16 L12 20 L12 12 M12 20 L21 16 L21 8", "stroke": "line"}, {"line": [7.5, 6, 16.5, 10], "stroke": "warm", "width": 1.25, "dash": [1.5, 2]}, {"d": "M3 8 L12 4 L21 8 L12 12 Z", "stroke": "accent", "width": 1.75}]}
@@ -0,0 +1 @@
+{"shapes": [{"d": "M3 6 L10.5 6 L10.5 18 L3 18 Z", "fill": "soft", "stroke": "line"}, {"d": "M13.5 6 L21 6 L21 18 L13.5 18 Z", "fill": "soft", "stroke": "line"}, {"line": [9, 8.5, 15, 8.5], "stroke": "warm", "width": 1.75}, {"line": [9, 12, 15, 12], "stroke": "warm", "width": 1.75}, {"line": [9, 15.5, 15, 15.5], "stroke": "warm", "width": 1.75}]}
@@ -0,0 +1 @@
+{"shapes": [{"d": "M4 6 L16 3 L20 15 L8 19 Z", "fill": "soft", "stroke": "line"}, {"d": "M8 5 L12.33 16.33 M12 4 L16.67 17.67 M5.33 10.33 L17.33 7 M6.67 14.67 L18.67 11", "stroke": "accent", "width": 1}]}
@@ -0,0 +1 @@
+{"shapes": [{"d": "M3 9 L9 5 L15 9 L9 13 Z", "fill": "soft", "stroke": "line"}, {"d": "M3 9 L3 17 L9 21 L9 13 M9 21 L15 17 L15 9", "stroke": "line"}, {"d": "M3 9 L9 21 M9 13 L15 17", "stroke": "line", "width": 1}, {"d": "M15 15 L21 15 M18.19 16.53 L21 15 L18.19 13.47", "stroke": "accent", "width": 1.5}]}
@@ -0,0 +1 @@
+{"shapes": [{"d": "M6 20 L18 20 L18 11.6 Q12 8.4 6 11.6 Z", "fill": "soft", "stroke": "line"}, {"d": "M6 17.2 L18 17.2 M6 14.4 Q12 12 18 14.4 M10 20 L10 9.9 M14 20 L14 9.9", "stroke": "accent", "width": 1}, {"d": "M3 9.2 Q12 3.4 21 9.2", "stroke": "accent", "width": 2}, {"d": "M12 6 L12 3 M10.5 4.5 L12 3 L13.5 4.5", "stroke": "line"}]}
@@ -0,0 +1 @@
+{"shapes": [{"d": "M12 2 L12 22", "stroke": "accent", "width": 1.25, "dash": [2, 1.5]}, {"d": "M10 5 L3 7 L3 17 L10 19 Z", "fill": "soft", "stroke": "line"}, {"d": "M3 12 L10 12 M6.5 6 L6.5 18", "stroke": "line", "width": 1}, {"d": "M14 5 L21 7 L21 17 L14 19 Z", "fill": "soft", "stroke": "line"}, {"d": "M14 12 L21 12 M17.5 6 L17.5 18", "stroke": "line", "width": 1}]}
@@ -0,0 +1 @@
+{"shapes": [{"circle": [12, 12, 9], "stroke": "line", "width": 1.25, "dash": [2, 2]}, {"d": "M5 12 L19 12 M12 5 L12 19", "stroke": "line", "width": 1.0}, {"d": "M7.5 8 L16.5 8 M7.5 16 L16.5 16 M8 7.5 L8 16.5 M16 7.5 L16 16.5", "stroke": "line", "width": 1.0}, {"circle": [12, 12, 2.4], "fill": "accent", "stroke": "accent"}]}
@@ -0,0 +1 @@
+{"shapes": [{"d": "M12 3 L20 7 L20 16 L12 20 L4 16 L4 7 Z", "fill": "soft", "stroke": "line"}, {"d": "M4 7 L12 11 L20 7 M12 11 L12 20", "stroke": "line"}, {"d": "M4 11.5 L12 15.5 L20 11.5 M8 9 L8 18 M16 9 L16 18", "stroke": "accent", "width": 1}, {"d": "M12 3 L12 5.4 M20 7 L15.2 7 M12 11 L12 8.6 M4 7 L8.8 7", "stroke": "accent", "width": 1}, {"d": "M8.8 7 A3.2 1.6 0 1 0 15.2 7 A3.2 1.6 0 1 0 8.8 7 Z", "stroke": "warm", "width": 1.5}]}
@@ -0,0 +1 @@
+{"shapes": [{"rect": [3, 3, 8, 8], "fill": "soft", "stroke": "line"}, {"rect": [13, 3, 8, 8], "fill": "soft", "stroke": "line"}, {"rect": [3, 13, 8, 8], "fill": "soft", "stroke": "line"}, {"d": "M13 14 L21 13 L20 21 L14 19 Z", "fill": "warm", "stroke": "line"}]}
@@ -0,0 +1 @@
+{"shapes": [{"d": "M4 3 L12 3 L16 7 L16 21 L4 21 Z", "fill": "soft", "stroke": "line"}, {"d": "M12 3 L12 7 L16 7", "stroke": "line"}, {"d": "M7 17 L7 14 M10 17 L10 11 M13 17 L13 13", "stroke": "accent", "width": 2}, {"d": "M15 15 L21 15 M18.19 16.53 L21 15 L18.19 13.47", "stroke": "accent", "width": 1.5}]}
@@ -85,6 +85,7 @@
 //! | tet4 | C3D4 (H) | | | |
 //! | tet10 | C3D10 (H) | | | |
 //! | wedge6 | C3D6 (H) | | | |
+//! | pyramid5 | C3D5 (H) | | | |
 //! | hex8 | C3D8, C3D8R, C3D8I (H) | | | |
 //! | hex20 | C3D20, C3D20R (H) | | | |
 //! | tri3, quad4 | | S3 / S3R, S4 / S4R | | |
@@ -148,7 +149,7 @@ use std::fmt::Write as _;

 use fieldcraft_model::{
    BeamProfile, BoundaryCondition, ContactSurfaces, CouplingKind, Elastic, Element, ElementKind, Hardening, Hyperelastic, InitialPenetration,
-    Integration, Load, Model, OutputVariable, Plastic, Procedure, Resolved, Section, SectionKind, Step, Symmetry, Target,
+    Integration, Load, Model, OutputVariable, Plastic, Procedure, Resolved, Section, SectionKind, Step, Target,
 };

 use crate::{Error, Result, unsupported};
@@ -193,6 +194,7 @@ pub fn write_resolved(model: &Model, r: &Resolved) -> Result<String> {
    d.couplings(model, r);
    d.contacts(model, r)?;
    d.ties(model)?;
+    d.equations(model, r)?;
    d.steps(model, r)?;
    Ok(d.out)
 }
@@ -230,11 +232,12 @@ pub fn element_type(kind: ElementKind, section: &Section) -> std::result::Result
        (S::Solid {}, _, true, true) => return Err("incompatible modes with reduced integration".into()),
        (S::Solid {}, _, _, true) => return Err(format!("incompatible modes on {} elements (hex8 only)", kind.name())),
        (S::Solid {}, K::Tet4, ..) => "C3D4",
-        (S::Solid {}, K::Tet10 | K::Wedge6, true, _) => {
+        (S::Solid {}, K::Tet10 | K::Wedge6 | K::Pyramid5, true, _) => {
            return Err(format!("reduced integration of {} elements (Abaqus has no reduced-integration variant)", kind.name()));
        }
        (S::Solid {}, K::Tet10, ..) => "C3D10",
        (S::Solid {}, K::Wedge6, ..) => "C3D6",
+        (S::Solid {}, K::Pyramid5, ..) => "C3D5",
        (S::Solid {}, K::Hex8, r, _) => ["C3D8", "C3D8R"][usize::from(r)],
        (S::Solid {}, K::Hex20, r, _) => ["C3D20", "C3D20R"][usize::from(r)],
        (S::Shell { .. }, K::Tri3, r, _) => ["S3", "S3R"][usize::from(r)],
@@ -370,9 +373,36 @@ fn check_expressible(model: &Model) -> Result<()> {
            bad.insert(format!("coupling `{name}`: an Abaqus distributing coupling always couples translations 1-3"));
        }
    }
+    for name in inclined_symmetries(model) {
+        if !model.steps().iter().all(|s| s.boundary_conditions.contains(name)) {
+            bad.insert(format!(
+                "boundary condition `{name}`: a symmetry plane not normal to X, Y or Z active in some steps only (it is written as `*EQUATION`, which is model data and holds in every step)"
+            ));
+        }
+    }
    unsupported(FORMAT, bad)
 }

+/// The symmetry conditions on inclined planes some step uses: linear equations rather than held
+/// degrees of freedom.
+fn inclined_symmetries(model: &Model) -> BTreeSet<&String> {
+    model
+        .boundary_conditions()
+        .iter()
+        .filter(|(n, bc)| {
+            matches!(bc, BoundaryCondition::Symmetry { plane, .. } if plane.axis().is_none()) && !model.boundary_condition_users(n).is_empty()
+        })
+        .map(|(n, _)| n)
+        .collect()
+}
+
+/// The boundary conditions of `names` that `*BOUNDARY` writes (inclined symmetry planes are
+/// `*EQUATION`s).
+fn held_conditions(model: &Model, names: &BTreeSet<String>) -> BTreeSet<String> {
+    let inclined = inclined_symmetries(model);
+    names.iter().filter(|n| !inclined.contains(n)).cloned().collect()
+}
+
 /// The property of a group of discrete elements.
 enum DiscreteProperty {
    Mass(f64),
@@ -1076,10 +1106,12 @@ impl Deck {
            match bc {
                BoundaryCondition::Fixed { .. } => self.line(&format!("{target}, ENCASTRE")),
                BoundaryCondition::Symmetry { plane, .. } => {
-                    let s = match plane {
-                        Symmetry::X => "XSYMM",
-                        Symmetry::Y => "YSYMM",
-                        Symmetry::Z => "ZSYMM",
+                    let s = match plane.axis() {
+                        Some(0) => "XSYMM",
+                        Some(1) => "YSYMM",
+                        Some(2) => "ZSYMM",
+                        // An inclined plane is an `*EQUATION` (model data), never here.
+                        _ => continue,
                    };
                    self.line(&format!("{target}, {s}"));
                }
@@ -1097,8 +1129,74 @@ impl Deck {
        Ok(())
    }

+    /// The inclined symmetry planes: one `*EQUATION` per node and held direction (n · u = 0, and
+    /// the rotations about the plane's axes at shell and beam nodes), whose first term Abaqus
+    /// eliminates; it is chosen among the degrees of freedom no boundary condition, coupling
+    /// or tie constrains ([`crate::symmetry_equations`]).
+    fn equations(&mut self, model: &Model, r: &Resolved) -> Result<()> {
+        let inclined = inclined_symmetries(model);
+        if inclined.is_empty() {
+            return Ok(());
+        }
+        let steps = model.steps();
+        // Per node and degree of freedom: the value it is held at in each step that holds it.
+        let mut held: BTreeMap<(u32, u8), Vec<f64>> = BTreeMap::new();
+        for step in steps {
+            for name in held_conditions(model, &step.boundary_conditions) {
+                let Some(bc) = model.boundary_condition(&name) else { continue };
+                for &node in r.target_nodes(bc.target()) {
+                    for dof in bc.dofs().list() {
+                        let v = if matches!(step.procedure, Procedure::Frequency { .. } | Procedure::Buckle { .. }) {
+                            0.0
+                        } else {
+                            bc.value(dof).unwrap_or(0.0)
+                        };
+                        held.entry((node, dof)).or_default().push(v);
+                    }
+                }
+            }
+        }
+        let mut dependent: BTreeSet<(u32, u8)> = BTreeSet::new();
+        for c in model.couplings().values().filter(|c| c.kind == CouplingKind::Kinematic) {
+            for &node in r.sets.get(&c.set).map(|s| s.nodes.as_slice()).unwrap_or_default() {
+                dependent.extend(c.dofs.list().into_iter().map(|d| (node, d)));
+            }
+        }
+        for t in model.ties().values() {
+            for &node in r.sets.get(&t.secondary).map(|s| s.nodes.as_slice()).unwrap_or_default() {
+                dependent.extend((1..=6).map(|d| (node, d)));
+            }
+        }
+        let state = |node: u32, dof: u8| {
+            if dependent.contains(&(node, dof)) {
+                return crate::Held::Sometimes;
+            }
+            match held.get(&(node, dof)) {
+                None => crate::Held::Free,
+                Some(v) if v.len() == steps.len() && v.iter().all(|x| *x == v[0]) => crate::Held::Always(v[0]),
+                Some(_) => crate::Held::Sometimes,
+            }
+        };
+        let mut problems = BTreeSet::new();
+        let equations = crate::symmetry_equations(model, r, inclined, &model.rotating_nodes(), state, &mut problems);
+        unsupported(FORMAT, problems)?;
+        self.comment("Symmetry planes not normal to X, Y or Z: per node, no motion along the normal (and no rotation about the plane's axes)");
+        for e in &equations {
+            self.line("*EQUATION");
+            self.line(&e.terms.len().to_string());
+            let mut fields = Vec::new();
+            for (dof, c) in &e.terms {
+                fields.push(format!("{}, {dof}", e.node));
+                fields.push(number(*c)?);
+            }
+            self.line(&fields.join(", "));
+        }
+        Ok(())
+    }
+
    /// Boundary conditions of a step against the state it starts from.
    fn step_boundaries(&mut self, model: &Model, r: &Resolved, base: &BTreeSet<String>, active: &BTreeSet<String>) -> Result<()> {
+        let (base, active) = (&held_conditions(model, base), &held_conditions(model, active));
        if active == base {
            self.comment("boundary conditions: as in the base state");
            Ok(())
@@ -1188,7 +1286,8 @@ impl Deck {
            BTreeSet::new()
        } else {
            let in_every_step = |n: &String| steps.iter().all(|s| s.boundary_conditions.contains(n));
-            model.boundary_conditions().iter().filter(|(n, bc)| holds_at_zero(bc) && in_every_step(n)).map(|(n, _)| n.clone()).collect()
+            let all = model.boundary_conditions().iter().filter(|(n, bc)| holds_at_zero(bc) && in_every_step(n)).map(|(n, _)| n.clone()).collect();
+            held_conditions(model, &all)
        };
        if !initial.is_empty() {
            self.comment("Initial state: boundary conditions active in every step");
@@ -16,7 +16,7 @@ pub mod nastran;
 use std::collections::{BTreeMap, BTreeSet};

 use fieldcraft_model::nodal::edge_pressure;
-use fieldcraft_model::{Diagnostic, Load, Model, Resolved, ResolvedDirection};
+use fieldcraft_model::{BoundaryCondition, Diagnostic, Load, Model, Resolved, ResolvedDirection};

 #[derive(Debug, Clone, PartialEq, thiserror::Error)]
 pub enum Error {
@@ -176,6 +176,120 @@ pub fn edge_pressure_loads<'a>(model: &Model, r: &Resolved, active: impl IntoIte
    Ok(out)
 }

+/// How a degree of freedom is constrained apart from the inclined symmetry planes, for choosing
+/// the dependent one of a plane's equation (formats eliminate it, so it may carry no other
+/// constraint).
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub(crate) enum Held {
+    Free,
+    /// Held at this value wherever the equation applies: it cannot depend on the others, and an
+    /// equation of held ones alone is redundant when the values satisfy it.
+    Always(f64),
+    /// Held in some steps only, or made dependent by a coupling or tie: it cannot be dependent,
+    /// nor can the equation be dropped.
+    Sometimes,
+}
+
+/// A linear equation Σ cⱼ u(node, dofⱼ) = 0 of an inclined symmetry plane, dependent degree of
+/// freedom first.
+#[derive(Debug, Clone, PartialEq)]
+pub(crate) struct Equation {
+    pub node: u32,
+    pub terms: Vec<(u8, f64)>,
+}
+
+/// A coefficient below this fraction of its row's largest is round-off of the elimination.
+const NEGLIGIBLE: f64 = 1e-12;
+
+/// The equations of the inclined symmetry conditions `names` (others are skipped), node by node
+/// in label order: n · u = 0 and, at a node in `rotating`, t₁ · θ = 0 and t₂ · θ = 0 for the
+/// plane's in-plane axes ([`fieldcraft_model::Symmetry`]). The rows of one node (several planes
+/// meet at an edge) are reduced against each other, so each has a dependent degree of freedom
+/// of its own: the largest coefficient among those `held` says are free. A row of held degrees
+/// of freedom only is left out when their values satisfy it; otherwise it is a problem, as is a
+/// row with none free that cannot be left out.
+pub(crate) fn symmetry_equations<'a>(
+    model: &Model,
+    r: &Resolved,
+    names: impl IntoIterator<Item = &'a String>,
+    rotating: &BTreeSet<u32>,
+    held: impl Fn(u32, u8) -> Held,
+    problems: &mut BTreeSet<String>,
+) -> Vec<Equation> {
+    let mut rows: BTreeMap<u32, Vec<(&str, [f64; 6])>> = BTreeMap::new();
+    let mut seen = BTreeSet::new();
+    for name in names {
+        if !seen.insert(name.as_str()) {
+            continue;
+        }
+        let Some(BoundaryCondition::Symmetry { target, plane }) = model.boundary_condition(name) else { continue };
+        let (Some(n), Some([t1, t2])) = (plane.inclined(), plane.in_plane()) else { continue };
+        for &node in r.target_nodes(target) {
+            let at = rows.entry(node).or_default();
+            at.push((name, [n[0], n[1], n[2], 0.0, 0.0, 0.0]));
+            if rotating.contains(&node) || target.reference_point().is_some() {
+                at.push((name, [0.0, 0.0, 0.0, t1[0], t1[1], t1[2]]));
+                at.push((name, [0.0, 0.0, 0.0, t2[0], t2[1], t2[2]]));
+            }
+        }
+    }
+    let mut out = Vec::new();
+    for (node, rows) in rows {
+        // The equations of this node so far: (dependent index, coefficients).
+        let mut done: Vec<(usize, [f64; 6])> = Vec::new();
+        for (name, mut c) in rows {
+            let scale = c.iter().fold(0.0f64, |m, v| m.max(v.abs()));
+            for (d, e) in &done {
+                let f = c[*d] / e[*d];
+                for k in 0..6 {
+                    c[k] -= f * e[k];
+                }
+                c[*d] = 0.0;
+            }
+            for v in &mut c {
+                if v.abs() <= NEGLIGIBLE * scale {
+                    *v = 0.0;
+                }
+            }
+            if c.iter().all(|v| *v == 0.0) {
+                continue;
+            }
+            let dof = |k: usize| k as u8 + 1;
+            let pivot = (0..6).filter(|&k| c[k] != 0.0 && held(node, dof(k)) == Held::Free).fold(None, |best: Option<usize>, k| match best {
+                Some(b) if c[b].abs() >= c[k].abs() => Some(b),
+                _ => Some(k),
+            });
+            let Some(pivot) = pivot else {
+                let mut residual = 0.0;
+                let mut size = 0.0;
+                let mut always = true;
+                for k in (0..6).filter(|&k| c[k] != 0.0) {
+                    match held(node, dof(k)) {
+                        Held::Always(v) => {
+                            residual += c[k] * v;
+                            size += (c[k] * v).abs();
+                        }
+                        _ => always = false,
+                    }
+                }
+                if !always {
+                    problems.insert(format!(
+                        "boundary condition `{name}`: at node {node} every degree of freedom the inclined symmetry plane relates is held in some steps only or follows a coupling or tie, so none can be eliminated by its equation"
+                    ));
+                } else if residual.abs() > 1e-9 * size {
+                    problems.insert(format!("boundary condition `{name}`: node {node} is held off the inclined symmetry plane"));
+                }
+                continue;
+            };
+            let mut terms = vec![(dof(pivot), c[pivot])];
+            terms.extend((0..6).filter(|&k| k != pivot && c[k] != 0.0).map(|k| (dof(k), c[k])));
+            out.push(Equation { node, terms });
+            done.push((pivot, c));
+        }
+    }
+    out
+}
+
 /// The global degree of freedom (1–6) a spring or dashpot direction acts along, when it is one
 /// (a vector or line along an axis counts: the sign does not matter to a spring).
 pub(crate) fn axis_dof(d: ResolvedDirection) -> Option<u8> {
@@ -36,7 +36,7 @@ impl Keyword {
    pub(crate) fn of(kind: ElementKind) -> Keyword {
        match kind {
            ElementKind::Hex20 => Keyword::SolidH20,
-            ElementKind::Tet4 | ElementKind::Tet10 | ElementKind::Wedge6 | ElementKind::Hex8 => Keyword::Solid,
+            ElementKind::Tet4 | ElementKind::Tet10 | ElementKind::Wedge6 | ElementKind::Pyramid5 | ElementKind::Hex8 => Keyword::Solid,
            ElementKind::Tri3 | ElementKind::Tri6 | ElementKind::Quad4 | ElementKind::Quad8 => Keyword::Shell,
            ElementKind::Rod2 | ElementKind::Rod3 | ElementKind::Beam2 => Keyword::Beam,
        }
@@ -64,6 +64,8 @@ pub(crate) fn order(kind: ElementKind) -> &'static [usize] {
        ElementKind::Tet4 => &[0, 1, 2, 3, 3, 3, 3, 3],
        ElementKind::Tet10 => &[0, 1, 2, 3, 4, 5, 6, 8, 9, 7],
        ElementKind::Wedge6 => &[1, 0, 3, 4, 2, 2, 5, 5],
+        // The degenerate hexahedron: the base, then the apex four times.
+        ElementKind::Pyramid5 => &[0, 1, 2, 3, 4, 4, 4, 4],
        ElementKind::Hex8 => &[0, 1, 2, 3, 4, 5, 6, 7],
        ElementKind::Hex20 => &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19],
    }
@@ -95,7 +97,7 @@ pub(crate) struct Elform {
 ///
 /// Solids: hex8 2 (eight-point), reduced 1 (one-point) with hourglass control, incompatible
 /// modes −18 (eight-point enhanced strain with incompatible modes); wedges 2 (as degenerate
-/// hexahedra), reduced 15 (two-point pentahedron); tet4 10 (one point, exact for a linear
+/// hexahedra), reduced 15 (two-point pentahedron); pyramids 2 (as degenerate hexahedra); tet4 10 (one point, exact for a linear
 /// tetrahedron), hybrid 13 (nodal pressure); tet10 16; hex20 23. Shells: quad4 16 (fully
 /// integrated), reduced 2 (one-point) with hourglass control; tri3 4 (C0 triangle); quad8 23;
 /// tri6 24. Rods: 3 (truss). 2D (in the XY plane): plane stress 12, plane strain 13, both one-point
@@ -122,6 +124,8 @@ pub(crate) fn elform(kind: ElementKind, section: &SectionKind, f: Formulation, s
                ElementKind::Hex8 => plain(2),
                ElementKind::Wedge6 if reduced => plain(15),
                ElementKind::Wedge6 => plain(2),
+                ElementKind::Pyramid5 if reduced => no("there is no reduced-integration form of"),
+                ElementKind::Pyramid5 => plain(2),
                ElementKind::Tet4 => plain(10),
                _ if reduced && kind.is_quadratic() => no("there is no reduced-integration form of"),
                ElementKind::Tet10 => plain(16),
@@ -40,7 +40,8 @@
 //!   LS-DYNA's defaults; a step without nonlinear geometry and hyperelastic materials in nonlinear
 //!   steps are refused); boundary conditions
 //!   as `*BOUNDARY_SPC_*_ID` (named) and `*BOUNDARY_PRESCRIBED_MOTION_*_ID` for non-zero
-//!   displacements; forces, moments and tractions as `*LOAD_NODE_SET`/`_POINT` from the
+//!   displacements, a symmetry plane not normal to X, Y or Z as `*BOUNDARY_SPC_*_ID` in a
+//!   `*DEFINE_COORDINATE_SYSTEM` whose x axis is the plane's normal; forces, moments and tractions as `*LOAD_NODE_SET`/`_POINT` from the
 //!   resolved nodal values; pressure as `*LOAD_SEGMENT_SET`; gravity as `*LOAD_BODY_X/Y/Z`
 //!   (with `*LOAD_BODY_PARTS` when it acts on a set); output as `*DATABASE_BINARY_D3PLOT`,
 //!   `*DATABASE_SPCFORC` and `*DATABASE_EXTENT_BINARY`.
@@ -1048,6 +1049,24 @@ fn boundary_condition(
            (r.reference_point_nodes.get(p).copied().ok_or_else(|| broken(format!("boundary condition `{name}`: reference point `{p}`")))?, "NODE")
        }
    };
+    // A symmetry plane not normal to an axis: held in a coordinate system whose x axis is its
+    // normal and whose xy plane holds its first in-plane axis (translation x, rotations y and z).
+    if let BoundaryCondition::Symmetry { plane, .. } = bc
+        && let (Some(n), Some([t1, _])) = (plane.inclined(), plane.in_plane())
+    {
+        *constraint_id = constraint_id.saturating_add(1);
+        let cid = *constraint_id;
+        d.line("*DEFINE_COORDINATE_SYSTEM");
+        d.header(&["cid", "xo", "yo", "zo", "xl", "yl", "zl", "cidl"]);
+        d.card([Field::from(cid), Field::from(0.0), Field::from(0.0), Field::from(0.0), Field::from(n[0]), Field::from(n[1]), Field::from(n[2])]);
+        d.header(&["xp", "yp", "zp"]);
+        d.card([Field::from(t1[0]), Field::from(t1[1]), Field::from(t1[2])]);
+        d.line(&format!("*BOUNDARY_SPC_{suffix}_ID"));
+        id_card(d, constraint_id, name);
+        d.header(&["nsid", "cid", "dofx", "dofy", "dofz", "dofrx", "dofry", "dofrz"]);
+        d.card([Field::from(entity), Field::from(cid)].into_iter().chain([1, 0, 0, 0, 1, 1].map(|v: i32| Field::from(v))));
+        return Ok(());
+    }
    let dofs = bc.dofs();
    // Held degrees of freedom (in a frequency step every constrained one is held).
    let held: Vec<u8> = dofs.list().into_iter().filter(|dof| !is_static || bc.value(*dof).is_none_or(|v| v == 0.0)).collect();
@@ -6,7 +6,7 @@
 //! data (the entries). What the model holds becomes:
 //!
 //! - nodes and reference points: `GRID`;
-//! - solids: `CTETRA` (tet4, tet10), `CPENTA` (wedge6), `CHEXA` (hex8, hex20) with `PSOLID`;
+//! - solids: `CTETRA` (tet4, tet10), `CPENTA` (wedge6), `CPYRAM` (pyramid5), `CHEXA` (hex8, hex20) with `PSOLID`;
 //!   shells: `CTRIA3`, `CQUAD4`, `CTRIA6`, `CQUAD8` with `PSHELL`; beams: `CBEAM` with `PBEAML`;
 //!   rods: `CROD` with `PROD`. Nastran numbers a 20-node hexahedron's mid-side nodes bottom
 //!   edges, vertical edges, top edges, where the model has bottom, top, vertical
@@ -22,6 +22,9 @@
 //!   the basic X axis through a `CORD2R`;
 //! - boundary conditions: per step, one constraint set of `SPC1` (held degrees of freedom) and
 //!   `SPC` (prescribed values); in a modes step every constrained degree of freedom is held;
+//!   symmetry about a plane not normal to X, Y or Z: one `MPC` set per step, an equation per node
+//!   and held direction (n · u = 0, and t · θ = 0 about the plane's two axes at shell and beam
+//!   grids), its dependent component one no `SPC` or rigid element constrains;
 //! - forces, moments and tractions: `FORCE` and `MOMENT` at the nodal values the model resolves,
 //!   so every writer and the solver share one distribution; pressure: `PLOAD4` per element face;
 //!   gravity: `GRAV`; a step with several loads combines them with `LOAD`;
@@ -110,6 +113,7 @@ pub fn element_card(kind: ElementKind) -> &'static str {
        ElementKind::Quad8 => "CQUAD8",
        ElementKind::Tet4 | ElementKind::Tet10 => "CTETRA",
        ElementKind::Wedge6 => "CPENTA",
+        ElementKind::Pyramid5 => "CPYRAM",
        ElementKind::Hex8 | ElementKind::Hex20 => "CHEXA",
    }
 }
@@ -241,6 +245,8 @@ type Constraints = BTreeMap<u32, [Option<f64>; 6]>;
 struct Subcase<'m> {
    step: &'m Step,
    spc: Option<u32>,
+    /// The equations of its inclined symmetry planes.
+    mpc: Option<u32>,
    load: Option<u32>,
    method: Option<u32>,
 }
@@ -269,6 +275,8 @@ struct Deck<'m> {
    dependent: BTreeMap<u32, (Dofs, &'m str)>,
    /// Constraint sets by id.
    spc_sets: Vec<(u32, Constraints)>,
+    /// Multipoint constraint sets (inclined symmetry planes) by id.
+    mpc_sets: Vec<(u32, Vec<crate::Equation>)>,
    /// Load name → load set id.
    load_sids: BTreeMap<&'m str, u32>,
    /// Combinations: (id, load set ids).
@@ -310,7 +318,7 @@ impl<'m> Deck<'m> {
            model,
            r,
            sol,
-            subcases: steps.into_iter().map(|step| Subcase { step, spc: None, load: None, method: None }).collect(),
+            subcases: steps.into_iter().map(|step| Subcase { step, spc: None, mpc: None, load: None, method: None }).collect(),
            problems,
            next_sid: 1,
            materials: BTreeMap::new(),
@@ -321,6 +329,7 @@ impl<'m> Deck<'m> {
            discrete: Vec::new(),
            dependent: BTreeMap::new(),
            spc_sets: Vec::new(),
+            mpc_sets: Vec::new(),
            load_sids: BTreeMap::new(),
            combinations: Vec::new(),
        }
@@ -587,6 +596,7 @@ impl<'m> Deck<'m> {
    /// One constraint set per distinct step constraint, checked against coupled nodes.
    fn plan_constraints(&mut self) -> Result<()> {
        let (model, r) = (self.model, self.r);
+        let rotating = model.rotating_nodes();
        // Conflicts, one problem per pair of definitions: the nodes they meet on.
        let mut clashes: BTreeMap<(&str, &str, &str), BTreeSet<u32>> = BTreeMap::new();
        let mut on_dependent: BTreeMap<(&str, &str), BTreeSet<u32>> = BTreeMap::new();
@@ -598,6 +608,10 @@ impl<'m> Deck<'m> {
            for name in &step.boundary_conditions {
                let Some(bc) = model.boundary_condition(name) else { continue };
                let dofs = bc.dofs();
+                // Inclined symmetry planes hold no global degree of freedom: they are equations.
+                if dofs.is_empty() {
+                    continue;
+                }
                // In a modes step every constrained degree of freedom is held.
                let values: Vec<(u8, f64)> = dofs.list().into_iter().filter_map(|d| Some((d, if modes { 0.0 } else { bc.value(d)? }))).collect();
                for &node in r.target_nodes(bc.target()) {
@@ -622,6 +636,19 @@ impl<'m> Deck<'m> {
                    }
                }
            }
+            let dependent = &self.dependent;
+            let held = |node: u32, dof: u8| match (
+                dependent.get(&node),
+                set.get(&node).and_then(|v| v.get(usize::from(dof).checked_sub(1)?).copied().flatten()),
+            ) {
+                (Some((d, _)), _) if d.contains(dof) => crate::Held::Sometimes,
+                (_, Some(v)) => crate::Held::Always(v),
+                _ => crate::Held::Free,
+            };
+            let equations = crate::symmetry_equations(model, r, &step.boundary_conditions, &rotating, held, &mut self.problems);
+            if !equations.is_empty() {
+                sub.mpc = Some(intern(&mut self.mpc_sets, &mut self.next_sid, equations)?);
+            }
            if !set.is_empty() {
                sub.spc = Some(intern(&mut self.spc_sets, &mut self.next_sid, set)?);
            }
@@ -707,7 +734,7 @@ impl<'m> Deck<'m> {
            let _ = writeln!(out, "SUBCASE {}", i + 1);
            let title: String = format!("  SUBTITLE = {}", sub.step.name).chars().take(72).collect();
            let _ = writeln!(out, "{title}");
-            for (key, sid) in [("SPC", sub.spc), ("LOAD", sub.load), ("METHOD", sub.method)] {
+            for (key, sid) in [("SPC", sub.spc), ("MPC", sub.mpc), ("LOAD", sub.load), ("METHOD", sub.method)] {
                if let Some(sid) = sid {
                    let _ = writeln!(out, "  {key} = {sid}");
                }
@@ -715,6 +742,7 @@ impl<'m> Deck<'m> {
            for v in &sub.step.output {
                let request = match v {
                    OutputVariable::Displacement => "DISPLACEMENT",
+                    OutputVariable::ReactionForce if sub.mpc.is_some() => "SPCFORCES = ALL\n  MPCFORCES",
                    OutputVariable::ReactionForce => "SPCFORCES",
                    OutputVariable::Stress => "STRESS",
                    OutputVariable::Strain => "STRAIN",
@@ -892,6 +920,23 @@ impl<'m> Deck<'m> {
                Card::new("SPC").int(*sid).int(node).int(component(Dofs::from_bits(mask))).real(value).write(out)?;
            }
        }
+        for (sid, equations) in &self.mpc_sets {
+            for sub in self.subcases.iter().filter(|s| s.mpc == Some(*sid)) {
+                comment(out, &format!("step {}: inclined symmetry planes, MPC {sid} (the first grid component is dependent)", sub.step.name));
+            }
+            for e in equations {
+                // SID, then (G, C, A) triples: two on the first line (its last field blank), two
+                // per continuation after a blank first field.
+                let mut card = Card::new("MPC").int(*sid);
+                for (i, (dof, c)) in e.terms.iter().enumerate() {
+                    if i % 2 == 0 && i > 0 {
+                        card = card.blank().blank();
+                    }
+                    card = card.int(e.node).int(i64::from(*dof)).real(*c);
+                }
+                card.write(out)?;
+            }
+        }
        Ok(())
    }

@@ -461,10 +461,11 @@ fn written_connectivity_has_a_positive_jacobian_in_abaqus_conventions() {
 #[test]
 fn model_faces_are_abaqus_faces() {
    // Each face's node positions (1-based, Abaqus element library, our transcription).
-    let table: [(ElementKind, &[&[usize]]); 3] = [
+    let table: [(ElementKind, &[&[usize]]); 4] = [
        (ElementKind::Hex8, &[&[1, 2, 3, 4], &[5, 8, 7, 6], &[1, 5, 6, 2], &[2, 6, 7, 3], &[3, 7, 8, 4], &[4, 8, 5, 1]]),
        (ElementKind::Tet4, &[&[1, 2, 3], &[1, 4, 2], &[2, 4, 3], &[3, 4, 1]]),
        (ElementKind::Wedge6, &[&[1, 2, 3], &[4, 6, 5], &[1, 4, 5, 2], &[2, 5, 6, 3], &[3, 6, 4, 1]]),
+        (ElementKind::Pyramid5, &[&[1, 2, 3, 4], &[1, 5, 2], &[2, 5, 3], &[3, 5, 4], &[4, 5, 1]]),
    ];
    for (kind, faces) in table {
        assert_eq!(kind.faces().len(), faces.len());
@@ -0,0 +1,193 @@
+//! Symmetry about a plane not normal to X, Y or Z in the three decks (#242): Abaqus `*EQUATION`s,
+//! Nastran `MPC` sets and an LS-DYNA `*BOUNDARY_SPC` in a local coordinate system, on a small
+//! shell plate of our own whose diagonal x = y is the plane.
+
+use fieldcraft_decks::{Error, abaqus, lsdyna, nastran};
+use fieldcraft_model::{
+    BoundaryCondition, Elastic, ElementFace, ElementKind, Formulation, Load, Material, Model, Procedure, Section, SectionKind, Set, Step, Symmetry,
+    Target,
+};
+
+/// A 2 × 2 quad4 shell plate in the XY plane (nodes 1–9, x and y in 0, 1, 2), clamped on x = 0,
+/// the inclined plane (normal (1, −1, 0)) on the diagonal nodes 1, 5 and 9, under pressure;
+/// steps `Load` (static) and `Modes`, `in_modes` saying whether the plane is active in both.
+fn plate(in_modes: bool) -> Model {
+    let mut m = Model::default();
+    for j in 0..3u32 {
+        for i in 0..3u32 {
+            m.set_node(1 + i + 3 * j, [f64::from(i), f64::from(j), 0.0]).unwrap();
+        }
+    }
+    for (e, n) in [(1, [1, 2, 5, 4]), (2, [2, 3, 6, 5]), (3, [4, 5, 8, 7]), (4, [5, 6, 9, 8])] {
+        m.set_element(e, ElementKind::Quad4, n.to_vec()).unwrap();
+    }
+    m.add_material(
+        "Steel",
+        Material { elastic: Some(Elastic::Isotropic { young: 210e3, poisson: 0.3 }), density: Some(7.85e-9), ..Material::default() },
+    )
+    .unwrap();
+    m.add_set("all", Set { elements: vec![1, 2, 3, 4], ..Set::default() }).unwrap();
+    let kind = SectionKind::Shell { thickness: 0.1, offset: 0.0, points: 5 };
+    m.add_section("plate", Section { set: "all".into(), material: "Steel".into(), kind, formulation: Formulation::default() }).unwrap();
+    m.add_set("edge", Set { nodes: vec![1, 4, 7], ..Set::default() }).unwrap();
+    m.add_set("diagonal", Set { nodes: vec![1, 5, 9], ..Set::default() }).unwrap();
+    let faces = (1..=4).map(|element| ElementFace { element, face: 1 }).collect();
+    m.add_set("top", Set { faces, ..Set::default() }).unwrap();
+    m.add_boundary_condition("clamp", BoundaryCondition::Fixed { target: Target::Set("edge".into()) }).unwrap();
+    let plane = Symmetry::from_normal([1.0, -1.0, 0.0]).unwrap();
+    m.add_boundary_condition("sym", BoundaryCondition::Symmetry { target: Target::Set("diagonal".into()), plane }).unwrap();
+    m.add_load("q", Load::Pressure { set: "top".into(), magnitude: 0.01 }).unwrap();
+    let mut load = Step::new("Load", Procedure::Static {});
+    load.boundary_conditions = ["clamp", "sym"].map(String::from).into();
+    load.loads = ["q".to_string()].into();
+    m.add_step(load, None).unwrap();
+    let mut modes = Step::new("Modes", Procedure::Frequency { modes: 3, min_hz: None, max_hz: None });
+    modes.boundary_conditions = if in_modes { ["clamp", "sym"].map(String::from).into() } else { ["clamp".to_string()].into() };
+    m.add_step(modes, None).unwrap();
+    m
+}
+
+/// A Nastran real: an exponent may come without `E`.
+fn real(s: &str) -> f64 {
+    let split = s.char_indices().skip(1).find(|(i, c)| (*c == '+' || *c == '-') && !s[..*i].ends_with(['E', 'e']));
+    match split {
+        Some((i, _)) => format!("{}E{}", &s[..i], &s[i..]).parse().unwrap(),
+        None => s.parse().unwrap(),
+    }
+}
+
+fn dot(a: [f64; 3], b: [f64; 3]) -> f64 {
+    (0..3).map(|k| a[k] * b[k]).sum()
+}
+
+/// Every equation is one of the plane's at a free node: its terms on one node, its coefficients
+/// along the normal (translations) or along an in-plane axis (rotations), unit length; nodes 5
+/// and 9 get three each (n · u, t₁ · θ, t₂ · θ); node 1 is clamped, so its equations are left out;
+/// no dependent degree of freedom repeats.
+fn check(equations: &[(u32, Vec<(u8, f64)>)]) {
+    let n = [1.0 / 2f64.sqrt(), -1.0 / 2f64.sqrt(), 0.0];
+    let mut dependents = std::collections::BTreeSet::new();
+    let mut per_node = std::collections::BTreeMap::<u32, usize>::new();
+    for (node, terms) in equations {
+        assert!(dependents.insert((*node, terms[0].0)), "{node} {terms:?}");
+        *per_node.entry(*node).or_default() += 1;
+        let mut v = [0.0; 3];
+        let rotation = terms[0].0 > 3;
+        for (dof, c) in terms {
+            assert_eq!(*dof > 3, rotation, "{terms:?}");
+            v[usize::from((dof - 1) % 3)] = *c;
+        }
+        assert!((dot(v, v) - 1.0).abs() < 1e-12, "{terms:?}");
+        if rotation {
+            assert!(dot(v, n).abs() < 1e-12, "{terms:?}");
+        } else {
+            assert!((dot(v, n).abs() - 1.0).abs() < 1e-12, "{terms:?}");
+        }
+    }
+    assert_eq!(per_node, [(5, 3), (9, 3)].into());
+}
+
+#[test]
+fn abaqus_writes_equations_in_the_model_data() {
+    let deck = abaqus::write(&plate(true)).unwrap();
+    let lines: Vec<&str> = deck.lines().collect();
+    let mut equations = Vec::new();
+    for (i, l) in lines.iter().enumerate() {
+        if *l == "*EQUATION" {
+            let count: usize = lines[i + 1].trim().parse().unwrap();
+            let f: Vec<&str> = lines[i + 2].split(',').map(str::trim).collect();
+            assert_eq!(f.len(), 3 * count, "{}", lines[i + 2]);
+            let node: u32 = f[0].parse().unwrap();
+            let terms = f.chunks(3).map(|t| (t[1].parse().unwrap(), t[2].parse().unwrap())).collect();
+            assert!(f.chunks(3).all(|t| t[0] == f[0]));
+            equations.push((node, terms));
+        }
+    }
+    check(&equations);
+    // Model data, before the first step; the plane is no `*BOUNDARY` line.
+    let first_step = deck.find("*STEP").unwrap();
+    assert!(deck.rfind("*EQUATION").unwrap() < first_step);
+    assert!(!deck.contains("SYMM"), "{deck}");
+
+    let e = abaqus::write(&plate(false)).unwrap_err();
+    assert!(matches!(&e, Error::Unsupported { what, .. } if what.contains("boundary condition `sym`") && what.contains("some steps only")), "{e}");
+}
+
+#[test]
+fn nastran_writes_one_mpc_set_per_step() {
+    // A static deck and a modes deck (one solution per run).
+    for (steps, sol) in [("Load", 101), ("Modes", 103)] {
+        let m = fieldcraft_decks::with_steps(&plate(true), &[steps.to_string()]).unwrap();
+        let deck = nastran::write(&m).unwrap();
+        assert!(deck.contains(&format!("SOL {sol}")));
+        let sid = deck.lines().find_map(|l| l.trim().strip_prefix("MPC = ")).unwrap().to_string();
+        // MPC entries: SID, then (grid, component, coefficient) triples; the continuation after
+        // two triples starts with a blank field. Large-field lines are 16 columns per field.
+        let mut equations = Vec::new();
+        let mut fields: Vec<String> = Vec::new();
+        let flush = |fields: &mut Vec<String>, equations: &mut Vec<(u32, Vec<(u8, f64)>)>| {
+            if fields.is_empty() {
+                return;
+            }
+            assert_eq!(fields[0], sid);
+            let data: Vec<&String> = fields[1..].iter().enumerate().filter(|(i, _)| !matches!(i % 8, 6 | 7)).map(|(_, f)| f).collect();
+            let triples: Vec<(u32, u8, f64)> = data
+                .chunks(3)
+                .filter(|t| t.len() == 3 && !t[0].is_empty())
+                .map(|t| (t[0].parse().unwrap(), t[1].parse().unwrap(), real(t[2])))
+                .collect();
+            assert!(triples.iter().all(|t| t.0 == triples[0].0));
+            equations.push((triples[0].0, triples.iter().map(|t| (t.1, t.2)).collect()));
+            fields.clear();
+        };
+        for line in deck.lines() {
+            let (head, rest) = line.split_at(8.min(line.len()));
+            let row: Vec<String> = rest.as_bytes().chunks(16).map(|c| String::from_utf8_lossy(c).trim().to_string()).collect();
+            let mut row = row;
+            row.resize(4, String::new());
+            match head.trim() {
+                "MPC*" => {
+                    flush(&mut fields, &mut equations);
+                    fields.extend(row);
+                }
+                "*" if !fields.is_empty() => fields.extend(row),
+                _ => flush(&mut fields, &mut equations),
+            }
+        }
+        flush(&mut fields, &mut equations);
+        check(&equations);
+    }
+}
+
+#[test]
+fn lsdyna_holds_the_plane_in_a_local_system() {
+    let deck = lsdyna::write(&plate(true)).unwrap().text;
+    let block = |keyword: &str| -> Vec<Vec<f64>> {
+        let at = deck.find(keyword).unwrap();
+        deck[at..]
+            .lines()
+            .skip(1)
+            .filter(|l| !l.starts_with('$'))
+            .take_while(|l| !l.starts_with('*'))
+            .map(|l| l.as_bytes().chunks(20).filter_map(|c| String::from_utf8_lossy(c).trim().parse().ok()).collect())
+            .collect()
+    };
+    let system = block("*DEFINE_COORDINATE_SYSTEM");
+    let (cid, x, p) = (system[0][0], [system[0][4], system[0][5], system[0][6]], [system[1][0], system[1][1], system[1][2]]);
+    assert!((x[0] + x[1]).abs() < 1e-12 && x[2] == 0.0 && (dot(x, x) - 1.0).abs() < 1e-12, "{x:?}");
+    assert!(dot(x, p).abs() < 1e-12, "{p:?}");
+    // The SPC after the system: its id card, then nsid, cid and the held local directions.
+    let at = deck.find("*DEFINE_COORDINATE_SYSTEM").unwrap();
+    let spc = deck[at..].find("*BOUNDARY_SPC_SET_ID").unwrap() + at;
+    let card: Vec<f64> = deck[spc..]
+        .lines()
+        .skip(2)
+        .find(|l| !l.starts_with('$'))
+        .unwrap()
+        .as_bytes()
+        .chunks(20)
+        .map(|c| String::from_utf8_lossy(c).trim().parse().unwrap())
+        .collect();
+    assert_eq!(card[1], cid);
+    assert_eq!(&card[2..], [1.0, 0.0, 0.0, 0.0, 1.0, 1.0]);
+}
@@ -17,7 +17,7 @@ use serde_json::{Value, json};
 use crate::crash::without_home;

 /// The issue form.
-pub const ISSUE_URL: &str = "https://github.com/jyviko/fieldcraft/issues/new";
+pub const ISSUE_URL: &str = "https://github.com/tangency-labs/fieldcraft/issues/new";
 /// The longest link a draft opens: GitHub refuses new-issue links much past 8 KB.
 pub const MAX_URL: usize = 7000;
 /// The session file a draft attaches.
@@ -329,7 +329,7 @@ mod tests {
            ..Default::default()
        };
        let d = draft(&input, "v1.2.3, testos x");
-        assert!(d.url.starts_with("https://github.com/jyviko/fieldcraft/issues/new?template=bug.yml&title="), "{}", d.url);
+        assert!(d.url.starts_with("https://github.com/tangency-labs/fieldcraft/issues/new?template=bug.yml&title="), "{}", d.url);
        assert!(d.attachments.is_empty() && d.clipboard.is_none(), "nothing attached without Share my session");
        let all = format!("{} {:?} {}", d.title, d.fields, decode(&d.url));
        assert!(!all.contains(&home()), "no home folder: {all}");
@@ -0,0 +1,130 @@
+//! A cancelled job ([`fieldcraft_model::progress::Progress::cancel`]) stops every solver and
+//! mesher promptly with `cancelled` and leaves the model as it was.
+
+use std::time::{Duration, Instant};
+
+use fieldcraft_geometry::sample::Plate;
+use fieldcraft_model::progress::{self, Progress};
+use serde_json::{Value, json};
+
+use crate::Session;
+use crate::sample::impact;
+
+/// How long a cancelled command may keep running: one increment, time step or pass, far
+/// below the minutes the runs below would take uncancelled.
+const PROMPT: Duration = Duration::from_secs(5);
+
+/// Run `command` on `s` the way a job does and cancel it once it reports the stage `stage`
+/// (mid-run), or before it starts (`None`): it must fail with `cancelled`, soon after, leaving
+/// the model and the journal as they were.
+fn cancel(s: &mut Session, command: &str, params: Value, stage: Option<&str>) {
+    let (model, journal) = (s.model.clone(), s.journal.len());
+    let p = Progress::new();
+    if stage.is_none() {
+        p.cancel();
+    }
+    let (r, waited) = std::thread::scope(|scope| {
+        let worker = {
+            let p = p.clone();
+            let s = &mut *s;
+            let params = params.clone();
+            scope.spawn(move || progress::scoped(Some(p), || s.execute(command, &params)))
+        };
+        let mut at = Instant::now();
+        if let Some(stage) = stage {
+            let deadline = Instant::now() + Duration::from_secs(600);
+            while !worker.is_finished() && Instant::now() < deadline {
+                let now = p.snapshot();
+                if now.stage.starts_with(stage) && now.done > 0.0 {
+                    at = Instant::now();
+                    p.cancel();
+                    break;
+                }
+                std::thread::sleep(Duration::from_millis(1));
+            }
+            assert!(p.is_cancelled(), "{command}: never reached stage `{stage}` ({:?})", p.snapshot());
+        }
+        let r = worker.join().unwrap();
+        (r, at.elapsed())
+    });
+    let e = r.expect_err(&format!("{command}: ran to the end although cancelled"));
+    assert!(e.is_cancelled(), "{command}: {e}");
+    assert_eq!(e.to_string(), "cancelled", "{command}");
+    assert!(waited < PROMPT, "{command}: stopped {waited:?} after the cancel");
+    assert!(s.model == model, "{command}: the model changed");
+    assert_eq!(s.journal.len(), journal, "{command}: journalled");
+}
+
+/// A sample's script run on a fresh session.
+fn session(script: &Value) -> Session {
+    let mut s = Session::default();
+    s.run_script(script).unwrap();
+    s
+}
+
+fn plate() -> (crate::tests::TempDir, Session) {
+    let (dir, path) = crate::tests::sample_design_file(&Plate::default());
+    let mut s = Session::default();
+    s.execute("geometry.open", &json!({"path": path})).unwrap();
+    (dir, s)
+}
+
+#[test]
+fn explicit_stops_between_time_steps() {
+    // A hundred times as long as the sample: hundreds of thousands of increments.
+    let mut script = impact();
+    for c in script.as_array_mut().unwrap() {
+        if c["command"] == "model.step.create" {
+            let p = &mut c["params"]["procedure"];
+            (p["end_time"], p["output_interval"], p["history_interval"]) = (json!(4e-3), json!(4e-4), json!(2e-5));
+        }
+    }
+    let mut s = session(&script);
+    cancel(&mut s, "solve.explicit", json!({}), Some("Time"));
+}
+
+#[test]
+fn fluid_stops_between_lattice_steps() {
+    let mut s = Session::default();
+    s.execute("file.sample", &json!({"name": "flow-past"})).unwrap();
+    cancel(&mut s, "solve.fluid", json!({}), Some("Fluid steps"));
+}
+
+#[test]
+fn nonlinear_stops_between_increments() {
+    let mut s = Session::default();
+    s.execute("file.sample", &json!({"name": "rubber-seal"})).unwrap();
+    cancel(&mut s, "solve.nonlinear", json!({}), Some("Load factor"));
+}
+
+#[test]
+fn transient_heat_stops_between_increments() {
+    let mut s = Session::default();
+    s.execute("file.sample", &json!({"name": "heated-bracket"})).unwrap();
+    s.execute(
+        "model.step.create",
+        &json!({"name": "Warm", "procedure": {"type": "heat_transfer", "transient": {"end_time": 1e5, "increment": 1}},
+            "boundary_conditions": ["Heater"], "loads": ["Air"]}),
+    )
+    .unwrap();
+    cancel(&mut s, "solve.heat", json!({"step": "Warm"}), Some("Time increment"));
+}
+
+#[test]
+fn static_frequency_and_solve_all_stop_at_the_factorization() {
+    let mut s = Session::default();
+    s.execute("file.sample", &json!({"name": "cantilever"})).unwrap();
+    cancel(&mut s, "solve.static", json!({}), None);
+    cancel(&mut s, "solve.frequency", json!({}), None);
+    cancel(&mut s, "solve.run", json!({}), None);
+}
+
+#[test]
+fn meshers_stop_and_leave_no_mesh() {
+    let (_dir, mut s) = plate();
+    cancel(&mut s, "mesh.tet.generate", json!({"body": "Body1", "size": 0.4}), Some("Refinement round"));
+    cancel(&mut s, "mesh.tet.generate", json!({"body": "Body1", "size": 2.5}), None);
+    cancel(&mut s, "mesh.hex.generate", json!({"body": "Body1", "size": 2.5}), None);
+    cancel(&mut s, "mesh.hex.octree", json!({"body": "Body1", "size": 5.0, "max_depth": 2}), None);
+    assert!(s.model.nodes().is_empty());
+}
@@ -238,8 +238,22 @@ pub static CATALOGUE: &[Capability] = &[
    // ---- Geometry ----
    ready("geometry.open", "Open Design", Geometry, "Import", "Open a SolidCraft design: its bodies with persistent face names"),
    ready("geometry.import.mesh", "Tagged Mesh", Geometry, "Import", "Read a face-tagged surface mesh (3MF)"),
-    ready("geometry.bodies", "Bodies", Geometry, "Inspect", "List the open design's bodies, volumes and named faces"),
+    ready_more(
+        "geometry.bodies",
+        "Bodies",
+        Geometry,
+        "Inspect",
+        "List the open design's bodies, volumes and named faces, edges and vertices",
+        &["geometry.centre", "geometry.features"],
+    ),
    ready("geometry.tessellate", "Tessellate", Geometry, "Inspect", "Tessellate a body into a face-tagged boundary surface"),
+    ready(
+        "geometry.check",
+        "Check Geometry",
+        Geometry,
+        "Inspect",
+        "Short edges, small and sliver faces and near faces against the element size, located",
+    ),
    ready(
        "mesh.surface.check",
        "Check Surface",
@@ -254,7 +268,7 @@ pub static CATALOGUE: &[Capability] = &[
        Geometry,
        "Prepare",
        "A datum plane: principal plane and offset, three points or datum points, point and normal, normal to an axis",
-        &["geometry.datum.edit", "geometry.datum.delete"],
+        &["geometry.datum.edit", "geometry.datum.delete", "geometry.datum.suppress"],
    ),
    covering(
        "geometry.datum.axis",
@@ -278,7 +292,38 @@ pub static CATALOGUE: &[Capability] = &[
        Geometry,
        "Prepare",
        "Cut bodies into cells by a datum plane; the two faces of each cut are paired by name",
-        &["geometry.partition.delete"],
+        &["geometry.partition.delete", "geometry.partition.suppress"],
+    ),
+    covering(
+        "geometry.faces.merge",
+        "Merge Faces",
+        Geometry,
+        "Prepare",
+        "Mesh adjacent faces as one (virtual topology): a fillet in pieces, a face split by an imprint; the B-rep is unchanged",
+        &["geometry.faces.merge.delete"],
+    ),
+    ready(
+        "geometry.face.absorb",
+        "Absorb Faces",
+        Geometry,
+        "Prepare",
+        "Absorb tiny and sliver faces into a neighbour for meshing, one picked or every one Check Geometry found",
+    ),
+    covering(
+        "geometry.face.split",
+        "Split Face",
+        Geometry,
+        "Prepare",
+        "Split a face along a datum plane for meshing only: two faces on its surface, the cut an edge between them",
+        &["geometry.face.split.delete"],
+    ),
+    covering(
+        "geometry.stitch",
+        "Stitch",
+        Geometry,
+        "Prepare",
+        "Close an imported surface's gaps under a tolerance: open points welded, T-junctions split",
+        &["geometry.stitch.delete"],
    ),
    soon("geometry.midsurface", "Midsurface", Geometry, "Prepare", "M8", "Extract midsurfaces of thin parts for shell meshes"),
    // ---- Mesh ----
@@ -322,9 +367,32 @@ pub static CATALOGUE: &[Capability] = &[
        "Partitioned Mesh",
        Mesh,
        "Structured Hex",
-        "One mesh of a partitioned part, a method per cell (hex, tet, or all hex as conforming blocks); cells joined across partitions",
+        "One mesh of a partitioned part, a method per cell (hex, tet, or all hex as conforming blocks); cells joined across partitions, tet cells to hex cells through conforming pyramids",
        &["mesh.hex.blocks"],
    ),
+    ready(
+        "mesh.hex.extrude",
+        "Extrude to Surface",
+        Mesh,
+        "Structured Hex",
+        "Hex layers from a meshed or planar section up to a curved target surface, following the side faces",
+    ),
+    ready_more(
+        "mesh.plan",
+        "Mesh Plan",
+        Mesh,
+        "Structured Hex",
+        "A hex-meshing plan from the features that built a body (sweeps, blocks, O-grids, layers, imprints, copies); saved, editable, applied with the structured meshers",
+        &["mesh.plan.apply"],
+    ),
+    ready_more(
+        "mesh.block",
+        "Mesh Block",
+        Mesh,
+        "Structured Hex",
+        "A mapped block of hex, wedge or quad elements between corner points; projection blocking (a block topology projected onto the part)",
+        &["mesh.hex.project"],
+    ),
    soon(
        "mesh.hex.decompose",
        "Decompose",
@@ -333,7 +401,6 @@ pub static CATALOGUE: &[Capability] = &[
        "M5",
        "Find sweepable and mappable regions of 3D parts (extruded cross-sections are already cut into blocks by Hex Mesh)",
    ),
-    soon("mesh.transition", "Transition", Mesh, "Structured Hex", "M5", "Conforming tet–hex interfaces with pyramids"),
    ready(
        "mesh.hex.octree",
        "Octree Hex",
@@ -346,20 +413,37 @@ pub static CATALOGUE: &[Capability] = &[
    soon("mesh.smooth", "Smooth", Mesh, "Improve", "M6", "Smooth node positions, keeping every element valid"),
    soon("mesh.untangle", "Untangle", Mesh, "Improve", "M6", "Repair inverted elements"),
    soon("mesh.layers", "Layers", Mesh, "Improve", "M6", "Boundary padding and layers through thin walls"),
-    ready_more("mesh.node.add", "Node", Mesh, "Edit", "Add a node", &["mesh.node.remove"]),
    ready_more(
-        "mesh.element.add",
-        "Element",
+        "mesh.node.relax",
+        "Relax Nodes",
+        Mesh,
+        "Improve",
+        "Relax the nodes inside a sphere to fix spikes and slivers; surface nodes slide on the geometry; kept as a field to apply again after a remesh",
+        &["mesh.node.relax.apply"],
+    ),
+    ready_more("mesh.node.add", "Node", Mesh, "Edit", "Add a node", &["mesh.node.remove"]),
+    ready_more("mesh.element.add", "Element", Mesh, "Edit", "Add an element on existing nodes", &["mesh.element.remove", "mesh.clear"]),
+    ready("mesh.mirror", "Mirror Mesh", Mesh, "Edit", "Mirror a body's mesh across a plane, joined on the plane (mesh half a symmetric part)"),
+    ready_more(
+        "mesh.node.merge",
+        "Merge Nodes",
        Mesh,
        "Edit",
-        "Add an element on existing nodes, or a mapped block of them",
-        &["mesh.element.remove", "mesh.block", "mesh.mirror"],
+        "Merge coincident nodes, keeping sets, loads and boundary conditions on the survivors; check for duplicates and cracks, renumber",
+        &["mesh.check.duplicates", "mesh.renumber"],
    ),
-    soon("mesh.node.merge", "Merge Nodes", Mesh, "Edit", "M6", "Merge coincident nodes"),
    soon("mesh.region.remesh", "Remesh Region", Mesh, "Edit", "M6", "Remesh a region in place; split and collapse elements"),
    soon("mesh.import.orphan", "Orphan Mesh", Mesh, "Edit", "M6", "Import a mesh without geometry"),
    ready("mesh.quality", "Quality", Mesh, "Verify", "Quality metrics and the certified validity check, failing elements listed"),
+    ready(
+        "mesh.quality.mark",
+        "Mark Bad Elements",
+        Mesh,
+        "Verify",
+        "Mark the elements below quality limits as a set, located and drawn in the marker colour",
+    ),
    soon("mesh.verify", "Verify Set", Mesh, "Verify", "M2", "Quality and validity per set"),
+    ready("mesh.export.stl", "Export STL", Mesh, "Verify", "Write the mesh's outer surface (or a set's faces) as binary STL"),
    ready_more("mesh.tag", "Tag Geometry", Mesh, "Verify", "Tag elements, faces, edges and nodes with the geometry they mesh", &["mesh.tag.clear"]),
    // ---- Properties ----
    ready_more(
@@ -498,7 +582,14 @@ pub static CATALOGUE: &[Capability] = &[
        "Contact",
        "Find the parts of the mesh that touch, and make contact pairs of them",
    ),
-    soon("interaction.rigid_wall", "Rigid Wall", Interactions, "Contact", "M10", "Rigid walls for explicit dynamics"),
+    ready_more(
+        "interaction.rigid_wall",
+        "Rigid Wall",
+        Interactions,
+        "Contact",
+        "A fixed rigid plane a set's nodes cannot pass, with friction, in an explicit dynamics step",
+        &["interaction.rigid_wall.delete"],
+    ),
    soon("interaction.bolt", "Bolt Load", Interactions, "Connectors", "M7", "Bolt pretension"),
    ready_more(
        "model.spring.create",
@@ -564,18 +655,21 @@ pub static CATALOGUE: &[Capability] = &[
        "Displacement, rotation, reaction and stress at nodes, element section forces, a mode shape, or an explicit field frame (or click the model)",
        &["solve.history"],
    ),
-    ready("results.reactions", "Reactions", Results, "Query", "Reaction force and moment sums per set"),
+    ready_more("results.reactions", "Reactions", Results, "Query", "Reaction force and moment sums per set", &["results.export.csv"]),
    soon("results.free_body", "Free Body", Results, "Query", "M9", "Free-body forces across a cut"),
-    soon("results.xy", "XY Plot", Results, "Plots", "M9", "Plot a quantity against time or another"),
+    ready("results.xy", "XY Plot", Results, "Plots", "Plot a quantity against the load factor, time or mode"),
    soon("results.path", "Path Plot", Results, "Plots", "M9", "Plot a quantity along a path"),
    soon("results.cut", "Cut", Results, "Plots", "M9", "Section cuts through the model"),
    soon("results.display_group", "Display Group", Results, "Plots", "M9", "Show and hide parts of the model"),
    soon("results.streamlines", "Streamlines", Results, "Plots", "M12", "Streamlines and flow fields"),
+    ready("results.export.vtu", "Export VTU", Results, "Files", "Write a solved step as VTK unstructured grids for ParaView"),
    soon("results.read", "Read Results", Results, "Files", "M9", "Read results in public formats"),
    soon("results.convergence", "Convergence", Results, "Files", "M9", "Mesh convergence studies"),
    // ---- Tools ----
-    ready("model.info", "Model Info", Tools, "Model", "Node and element counts and the model summary"),
-    ready("file.open", "Open Model", Tools, "File", "Open a .fieldcraft model"),
+    // Renaming starts from a definition's item menu (Rename…); the search finds it here too.
+    ready_more("model.info", "Model Info", Tools, "Model", "Node and element counts and the model summary", &["model.rename"]),
+    // New starts from the File menu; the search finds it here too.
+    ready_more("file.open", "Open Model", Tools, "File", "Open a .fieldcraft model", &["file.new"]),
    ready("file.sample", "Samples", Tools, "File", "Open a sample model, ready to solve"),
    ready("file.save", "Save", Tools, "File", "Save the model to its .fieldcraft file"),
    ready("file.save_as", "Save As", Tools, "File", "Save the model to a new .fieldcraft file"),
@@ -604,7 +698,7 @@ pub static CATALOGUE: &[Capability] = &[
        Tools,
        "Help",
        "Draft a GitHub bug report with the version, the OS and the last error; you review it, and nothing is sent until you submit it",
-        &["diagnostics.crash_reports", "diagnostics.crash_report", "diagnostics.crash_test", "app.update.check"],
+        &["diagnostics.crash_reports", "diagnostics.crash_report", "diagnostics.crash_reports.delete", "diagnostics.crash_test", "app.update.check"],
    ),
 ];

@@ -2,13 +2,23 @@
 //! typically made by `geometry.partition`) with its own method, all into one mesh, and the cells
 //! joined across the partitions that divide them.
 //!
+//! **Sweeping together (#288).** The cells of one body of the design whose method may sweep
+//! (`auto`, `hex`, `swept`, `extrude`, `revolve`) are first meshed together
+//! ([`hex_mesh_swept_cells`]): one cross-section with every cell's cut faces imprinted, one
+//! interval assignment and one set of layers, so cells meet node for node across every cut — a
+//! cut that ends on another included — with no edge seeds, and their nodes are shared. When they
+//! do not sweep together in one frame (the reply says why, per cell, as `not_swept_together`),
+//! each cell is meshed alone as below.
+//!
 //! **Joining.** Two cells on either side of a partition `P` meet on faces named
 //! `partition:P:a` and `partition:P:b`. Where the element faces of the two sides match node for
 //! node (the same divisions and kind on both sides, e.g. a mesh and its mirror image) the
 //! coincident nodes are merged and the mesh is conforming there. Elsewhere — a hex cell next to a
-//! tet cell, or two cells meshed with different divisions — the two surfaces are tied: a set on
-//! each side's partition faces and a tie between them (`interaction.tie`; dual mortar
-//! constraints in the implicit analyses, so a constant stress crosses the interface exactly).
+//! tet cell, or two cells meshed with different divisions — the two surfaces are tied
+//! (`interaction.tie`; dual mortar constraints in the implicit analyses, so a constant stress
+//! crosses the interface exactly). Each tie goes one way, by a fixed order of the cells (hex cells
+//! main to tet cells), and each cell's tied cut faces make one tie, so no node is a secondary
+//! node of two of them and no interface is tied both ways: either would over-constrain it (#389).
 //! The tie is the transition between hex and tet cells; pyramid elements are not used, because
 //! they need their own element formulation in every solver and deck, while the tie works for any
 //! pair of meshes and keeps each cell's mesh as its method made it. The reply lists every
@@ -17,20 +27,22 @@
 use std::collections::{BTreeMap, BTreeSet};

 use fieldcraft_mesh::cdt::CdtOptions;
-use fieldcraft_mesh::hex::{HexMesh, HexMethod};
+use fieldcraft_mesh::hex::{Cell, CellsMesh, HexMesh, HexMethod, HexOptions, hex_mesh_swept_cells};
+use fieldcraft_mesh::size::UniformSize;
+use fieldcraft_mesh::surface::BoundarySurface;
 use fieldcraft_model::geometry::Entity;
 use fieldcraft_model::{ElementFace, GeometryRef, Model, Set, Tie};
 use serde_json::{Value, json};

-use super::hex::{Input, add_hex, hex_body};
-use super::mesh::{BodyTets, add_tets, mesh_body, quality_options};
+use super::hex::{Input, add_cells, add_hex, hex_body};
+use super::mesh::{add_tets, mesh_body, quality_options};
 use crate::requirement::Requirement;
 use crate::{CommandKind, CommandSpec, EngineError, Result, Session};

 pub const CELLS: CommandSpec = CommandSpec {
    id: "mesh.cells",
    label: "Partitioned Mesh",
-    params: r#"{"methods": {"Body1/a": "tet", "Body1/b": "swept"} (per cell; default `default`), "default": "auto", "bodies": ["Body1/a", "Body1/b"] (default: every body of the open design), "size": 2.0 (element size, mm; default 1/25 of the bounding-box diagonal of all of them), "order": 1 | 2 (hex8 and tet4, or hex20 and tet10), "tolerance": 0.05 (chordal tolerance, mm)} — replaces the cells' meshes (as mesh.tet.generate; other bodies keep theirs) with one mesh of the cells, each with its method: "auto" (structured hex where a method fits, else tet), "hex" (any structured hex method), "swept", "extrude", "sweep", "revolve", "mapped" or "tet"; or "default": "blocks" (with no `methods`): every cell a mapped block, division counts assigned over all cells together, exactly mesh.hex.blocks with the same parameters. Cells on either side of a partition (faces `partition:<name>:a` and `:b`) are joined: where their element faces match node for node the nodes are merged (conforming); otherwise, as between a hex and a tet cell, a set on each side and a tie between them are made (`tie_<partition>_<k>`, sets `<tie>_main` and `<tie>_secondary`: the side with fewer nodes is the main surface), replacing ties of those names from an earlier run. Reports each cell's method (and why auto fell back to tet), and each interface: `merged` with the nodes merged, or `tied`"#,
+    params: r#"{"methods": {"Body1/a": "tet", "Body1/b": "swept"} (per cell; default `default`), "default": "auto", "bodies": ["Body1/a", "Body1/b"] (default: every body of the open design), "size": 2.0 (element size, mm; default 1/25 of the bounding-box diagonal of all of them), "order": 1 | 2 (hex8 and tet4, or hex20 and tet10), "tolerance": 0.05 (chordal tolerance, mm), "transition": "pyramid" | "tie" (how a tet cell meets hex cells; default pyramid)} — replaces the cells' meshes (as mesh.tet.generate; other bodies keep theirs) with one mesh of the cells, each with its method: "auto" (structured hex where a method fits, else tet), "hex" (any structured hex method), "swept", "extrude", "sweep", "revolve", "mapped" or "tet"; or "default": "blocks" (with no `methods`): every cell a mapped block, division counts assigned over all cells together, exactly mesh.hex.blocks with the same parameters. Cells on either side of a partition (faces `partition:<name>:a` and `:b`) are joined: where their element faces match node for node the nodes are merged (conforming); between a tet cell and the hex cells across its partitions, with "transition": "pyramid" (linear meshes), the tet cell is meshed after them with a pyramid (pyramid5) on every hex element face of the cut, its tetrahedra sharing the pyramids' sides, so the mesh is conforming there (`joined`: `pyramids`, with their count); where that cannot be built (a cut the hex faces do not cover exactly, quadratic elements, a pyramid that would reach through a thin cell) the cell says why in `no_pyramids` and is tied; otherwise, as between a hex and a tet cell with "transition": "tie", they are tied: each cell's tied cut faces make one tie, `tie_<cell>` (`/` as `_`; sets `<tie>_main`, the facing cells' cut faces, and `<tie>_secondary`, the cell's own), hex cells main to tet cells and otherwise by name, so a node is a secondary node of one such tie only; the ties an earlier run made on these cells are replaced. The cells of one design body that may sweep (auto, hex, swept, extrude, revolve) are swept together first: one cross-section and one set of layers for all of them, so they share their nodes across every cut, T-junctions included, with no edge seeds (`swept_together` names the body; `not_swept_together` says why not, and those cells are meshed one by one). Reports each cell's method (and why auto fell back to tet), its `quality` (volume, smallest and mean scaled Jacobian, largest edge ratio), and each interface: `merged` with the nodes merged or shared, or `tied` (with `why` when both cells are of one design body: the tet cell and why auto fell back, or why the body's cells were not swept together)"#,
    form: Some(super::forms::CELLS),
    kind: CommandKind::Model,
    requires: &[Requirement::Design],
@@ -68,10 +80,22 @@ impl Method {
    }
 }

-/// A meshed cell.
+mod transition;
+
+/// A meshed cell; tet cells are meshed after the hex cells are in the model, so they can meet
+/// them through pyramids.
 enum Meshed<'a> {
-    Hex(Input<'a>, HexMesh),
-    Tet(BodyTets),
+    Hex(Box<(Input<'a>, HexMesh)>),
+    Tet,
+}
+
+/// How a tet cell joins the hex cells across its partitions.
+#[derive(Clone, Copy, PartialEq, Eq)]
+enum Transition {
+    /// Pyramids on the hex faces, conforming (falls back to a tie with the reason).
+    Pyramid,
+    /// A tie (dual mortar), each mesh as its method made it.
+    Tie,
 }

 fn cells(s: &mut Session, p: &Value) -> Result<Value> {
@@ -93,6 +117,11 @@ fn cells(s: &mut Session, p: &Value) -> Result<Value> {
            _ => return Err(EngineError::invalid("order", "must be 1 or 2")),
        },
    };
+    let transition = match p.get("transition").map(|v| v.as_str()) {
+        None | Some(Some("pyramid")) => Transition::Pyramid,
+        Some(Some("tie")) => Transition::Tie,
+        Some(_) => return Err(EngineError::invalid("transition", "must be \"pyramid\" or \"tie\"")),
+    };
    let default = p.get("default").map(Method::parse).transpose()?.unwrap_or(Method::Auto);
    let methods: BTreeMap<String, Method> = match p.get("methods") {
        None => BTreeMap::new(),
@@ -148,33 +177,81 @@ fn cells(s: &mut Session, p: &Value) -> Result<Value> {
    let cdt = CdtOptions { max_steiner: s.limits.max_steiner, max_tets: tet_options.max_tets };

    let seeds = super::seeds::edge_seeds(s)?;
+    let method_of = |n: &str| methods.get(n).copied().unwrap_or(default);
+    // The cells of one body that may sweep are swept together first (#288): one cross-section
+    // and one set of layers for all of them, so they meet node for node across their cuts. Cells
+    // that do not sweep together are meshed one by one, as below.
+    let mut groups: BTreeMap<(String, HexMethod), Vec<usize>> = BTreeMap::new();
+    for (i, shape) in shapes.iter().enumerate() {
+        let sweep = match method_of(&shape.name) {
+            Method::Auto | Method::Hex(HexMethod::Auto | HexMethod::Swept) => Some(HexMethod::Swept),
+            Method::Hex(m @ (HexMethod::Extrude | HexMethod::Revolve)) => Some(m),
+            Method::Hex(_) | Method::Tet => None,
+        };
+        if let (Some(m), Some(source)) = (sweep, design.source_of(&shape.name)) {
+            groups.entry((source.to_string(), m)).or_default().push(i);
+        }
+    }
+    let mut joint: Vec<Option<usize>> = vec![None; shapes.len()];
+    let mut not_together: BTreeMap<usize, String> = BTreeMap::new();
+    let mut swept: Vec<(String, Vec<usize>, Vec<Input>, CellsMesh)> = Vec::new();
+    for ((source, m), members) in groups {
+        if members.len() < 2 {
+            continue;
+        }
+        let inputs: Vec<Input> = members
+            .iter()
+            .filter_map(|&i| shapes.get(i))
+            .map(|shape| Ok(Input { seeds: seeds.clone(), ..super::hex::shape_input(shape, Some(tolerance))? }))
+            .collect::<Result<_>>()?;
+        match swept_together(p, &inputs, m, quadratic, size, tolerance, &seeds)? {
+            Ok(cm) => {
+                for &i in &members {
+                    if let Some(slot) = joint.get_mut(i) {
+                        *slot = Some(swept.len());
+                    }
+                }
+                swept.push((source, members, inputs, cm));
+            }
+            Err(why) => {
+                for &i in &members {
+                    not_together.insert(i, why.clone());
+                }
+            }
+        }
+    }
    let mut meshed: Vec<(Meshed, Value)> = Vec::with_capacity(shapes.len());
-    for shape in shapes {
-        let method = methods.get(&shape.name).copied().unwrap_or(default);
+    for (i, shape) in shapes.iter().enumerate() {
+        if joint.get(i).copied().flatten().is_some() {
+            continue;
+        }
+        let method = method_of(&shape.name);
        let input = || Ok::<_, EngineError>(Input { seeds: seeds.clone(), ..super::hex::shape_input(shape, Some(tolerance))? });
        let hex = |m: HexMethod| -> Result<(Input<'static>, HexMesh)> {
            let b = input()?;
            let mesh = hex_body(&hex_params, &b, m, quadratic, size)?;
            Ok((b, mesh))
        };
-        let tet = |s: &Session| mesh_body(s, &tet_params, input()?, &cdt, &tet_options, quality, true);
        let (cell, mut info) = match method {
            Method::Hex(m) => {
                let (b, mesh) = hex(m)?;
                let info = json!({"method": mesh.report.method.name()});
-                (Meshed::Hex(b, mesh), info)
+                (Meshed::Hex(Box::new((b, mesh))), info)
            }
-            Method::Tet => (Meshed::Tet(tet(s)?), json!({"method": "tet"})),
+            Method::Tet => (Meshed::Tet, json!({"method": "tet"})),
            Method::Auto => match hex(HexMethod::Auto) {
                Ok((b, mesh)) => {
                    let info = json!({"method": mesh.report.method.name()});
-                    (Meshed::Hex(b, mesh), info)
+                    (Meshed::Hex(Box::new((b, mesh))), info)
                }
-                Err(e) => (Meshed::Tet(tet(s)?), json!({"method": "tet", "why": e.to_string()})),
+                Err(e) => (Meshed::Tet, json!({"method": "tet", "why": e.to_string()})),
            },
        };
        if let Some(o) = info.as_object_mut() {
            o.insert("body".into(), json!(shape.name));
+            if let Some(why) = not_together.get(&i) {
+                o.insert("not_swept_together".into(), json!(why));
+            }
        }
        meshed.push((cell, info));
    }
@@ -183,14 +260,65 @@ fn cells(s: &mut Session, p: &Value) -> Result<Value> {
    // and the definitions stay.
    let model = &mut s.model;
    let cleared = super::replace::clear(model, names.iter().map(String::as_str));
-    let mut report = Vec::with_capacity(meshed.len());
-    for (cell, mut info) in meshed {
-        let (kind, elements, nodes) = match &cell {
-            Meshed::Hex(b, m) => {
+    let mut report: Vec<(usize, Value)> = Vec::with_capacity(shapes.len());
+    let mut interfaces = Vec::new();
+    for (source, members, inputs, cm) in &swept {
+        add_cells(model, inputs, cm)?;
+        let m = &cm.mesh;
+        for (c, (&i, b)) in members.iter().zip(inputs).enumerate() {
+            let elements: Vec<usize> = (0..m.element_count()).filter(|&e| cm.element_cell.get(e).is_some_and(|&x| x as usize == c)).collect();
+            let nodes: BTreeSet<u32> = elements.iter().filter_map(|&e| m.element(e)).flatten().copied().collect();
+            report.push((
+                i,
+                json!({"body": b.name, "method": m.report.method.name(), "swept_together": source, "description": m.report.description, "kind": m.kind.name(), "elements": elements.len(), "nodes": nodes.len()}),
+            ));
+        }
+        interfaces.extend(swept_interfaces(&design, inputs, cm));
+    }
+    // The cells meshed alone, in the order of `shapes`: the hex ones first, then the tet ones,
+    // which may meet the hex cells through pyramids.
+    let alone: Vec<usize> = (0..shapes.len()).filter(|&i| joint.get(i).copied().flatten().is_none()).collect();
+    let mut hex_cells: Vec<String> = swept.iter().flat_map(|(_, _, inputs, _)| inputs.iter().map(|b| b.name.clone())).collect();
+    let mut tet_cells = Vec::new();
+    for (&i, (cell, info)) in alone.iter().zip(meshed.iter_mut()) {
+        let mut info = std::mem::take(info);
+        match &*cell {
+            Meshed::Hex(hex) => {
+                let (b, m) = &**hex;
                add_hex(model, b, m)?;
-                (m.kind, m.element_count(), m.nodes.len())
+                hex_cells.push(b.name.clone());
+                if let Some(o) = info.as_object_mut() {
+                    o.insert("kind".into(), json!(m.kind.name()));
+                    o.insert("elements".into(), json!(m.element_count()));
+                    o.insert("nodes".into(), json!(m.nodes.len()));
+                }
+                report.push((i, info));
            }
-            Meshed::Tet(t) => {
+            Meshed::Tet => tet_cells.push((i, info)),
+        }
+    }
+    for (i, mut info) in tet_cells {
+        let Some(shape) = shapes.get(i) else { continue };
+        let input = Input { seeds: seeds.clone(), ..super::hex::shape_input(shape, Some(tolerance))? };
+        let pyramids = if transition == Transition::Tie {
+            Err("`transition` is \"tie\"".to_string())
+        } else if quadratic {
+            Err("pyramid transitions are linear (pyramid5); order 2 is tied".to_string())
+        } else {
+            transition::mesh_with_pyramids(&design, model, &tet_params, &input, &hex_cells, &cdt, &tet_options)?
+        };
+        let (kind, elements, nodes) = match pyramids {
+            Ok(c) => {
+                interfaces.extend(c.interfaces.iter().cloned());
+                let kind = c.tets.mesh.kind;
+                let (elements, nodes) = transition::add(model, c)?;
+                (kind, elements, nodes)
+            }
+            Err(why) => {
+                if let Some(o) = info.as_object_mut() {
+                    o.insert("no_pyramids".into(), json!(why));
+                }
+                let t = mesh_body(Some(&design), &tet_params, input, &cdt, &tet_options, quality, true)?;
                add_tets(model, &t.name, &t.face_names, &t.mesh)?;
                (t.mesh.kind, t.mesh.elements.len(), t.mesh.points.len())
            }
@@ -200,13 +328,136 @@ fn cells(s: &mut Session, p: &Value) -> Result<Value> {
            o.insert("elements".into(), json!(elements));
            o.insert("nodes".into(), json!(nodes));
        }
-        report.push(info);
+        report.push((i, info));
    }
-    let interfaces = join(model, &names, COINCIDENT * diagonal)?;
+    report.sort_by_key(|r| r.0);
+    let report: Vec<Value> = report
+        .into_iter()
+        .map(|(_, mut info)| {
+            let quality = info.get("body").and_then(Value::as_str).map(|b| cell_quality(model, b));
+            if let (Some(o), Some(q)) = (info.as_object_mut(), quality) {
+                o.insert("quality".into(), q);
+            }
+            info
+        })
+        .collect();
+    let tet: BTreeSet<String> = report
+        .iter()
+        .filter(|r| r.get("kind").and_then(Value::as_str).is_some_and(|k| k.starts_with("tet")))
+        .filter_map(|r| r.get("body").and_then(Value::as_str).map(String::from))
+        .collect();
+    interfaces.extend(join(model, &names, &tet, COINCIDENT * diagonal)?);
+    explain_ties(&design, &report, &mut interfaces);
    let (nodes, elements) = (model.nodes().len(), model.elements().len());
    Ok(cleared.report(s, json!({"cells": report, "interfaces": interfaces, "nodes": nodes, "elements": elements, "size": size})))
 }

+/// Sweep the cells `inputs` together ([`hex_mesh_swept_cells`]) with `method` (extrude,
+/// revolve, or swept: either). `Ok(Err(why))` when they do not sweep together; limits and a
+/// cancel are errors.
+fn swept_together(
+    p: &Value,
+    inputs: &[Input],
+    method: HexMethod,
+    quadratic: bool,
+    size: Option<f64>,
+    tolerance: f64,
+    seeds: &[fieldcraft_mesh::seeds::EdgeSeed],
+) -> Result<std::result::Result<CellsMesh, String>> {
+    let h = size.ok_or_else(|| EngineError::Params("no element size".into()))?;
+    let mut surfaces = Vec::with_capacity(inputs.len());
+    for b in inputs {
+        let options = super::mesh::surface_options(p, &b.mesh)?;
+        match BoundarySurface::new(&b.mesh.positions, &b.mesh.triangles, &b.mesh.tri_face, &options) {
+            Ok(surface) => surfaces.push(surface),
+            Err(e) => return Ok(Err(format!("body `{}`: {e}", b.name))),
+        }
+    }
+    let cells: Vec<Cell> = surfaces.iter().zip(inputs).map(|(surface, b)| Cell { name: &b.name, surface, faces: &b.surfaces }).collect();
+    let options = HexOptions {
+        method,
+        quadratic,
+        chordal_tolerance: tolerance,
+        max_elements: fieldcraft_model::MAX_ELEMENTS / 8,
+        seeds: seeds.to_vec(),
+        ..HexOptions::default()
+    };
+    match hex_mesh_swept_cells(&cells, &UniformSize(h), &options) {
+        Ok(cm) => Ok(Ok(cm)),
+        Err(fieldcraft_mesh::Error::Model(fieldcraft_model::Error::Cancelled)) => Err(EngineError::Model(fieldcraft_model::Error::Cancelled)),
+        Err(e @ fieldcraft_mesh::Error::Limit(_)) => Err(EngineError::Params(e.to_string())),
+        Err(e) => Ok(Err(e.to_string())),
+    }
+}
+
+/// The interfaces of cells swept together: each pair of cells whose elements share faces, with
+/// the partition between them and the nodes they share (one mesh: merged by construction).
+fn swept_interfaces(design: &fieldcraft_geometry::Design, inputs: &[Input], cm: &CellsMesh) -> Vec<Value> {
+    let m = &cm.mesh;
+    let mut owner: BTreeMap<[u32; 4], u32> = BTreeMap::new();
+    let mut pairs: BTreeMap<(u32, u32), BTreeSet<u32>> = BTreeMap::new();
+    for e in 0..m.element_count() {
+        let (Some(h), Some(&c)) = (m.element(e), cm.element_cell.get(e)) else { continue };
+        for local in fieldcraft_model::ElementKind::Hex8.faces() {
+            let mut key = [0u32; 4];
+            for (slot, &i) in key.iter_mut().zip(local.iter()) {
+                *slot = h.get(i).copied().unwrap_or(0);
+            }
+            key.sort_unstable();
+            match owner.insert(key, c) {
+                Some(o) if o != c => pairs.entry((o.min(c), o.max(c))).or_default().extend(key),
+                _ => {}
+            }
+        }
+    }
+    // The partitions whose cut faces a cell has, with the side: two cells meet across a
+    // partition they are on opposite sides of.
+    let cuts = |c: u32| -> BTreeSet<(String, String)> {
+        let name = inputs.get(c as usize).map_or("", |b| b.name.as_str());
+        let faces = design.body(name).map(|b| b.faces().iter().map(|f| f.name.clone()).collect::<Vec<_>>()).unwrap_or_default();
+        faces
+            .iter()
+            .filter_map(|f| {
+                let (p, side) = f.strip_prefix("partition:")?.rsplit_once(':')?;
+                let side = side.split_once('#').map_or(side, |(s, _)| s);
+                Some((p.to_string(), side.to_string()))
+            })
+            .collect()
+    };
+    pairs
+        .into_iter()
+        .map(|((a, b), nodes)| {
+            let (na, nb) = (inputs.get(a as usize).map_or("", |x| x.name.as_str()), inputs.get(b as usize).map_or("", |x| x.name.as_str()));
+            let theirs = cuts(b);
+            let partition =
+                cuts(a).into_iter().find(|(p, side)| theirs.iter().any(|(q, other)| q == p && other != side)).map(|(p, _)| p).unwrap_or_default();
+            json!({"partition": partition, "cells": [na, nb], "joined": "merged", "nodes": nodes.len(), "swept_together": true})
+        })
+        .collect()
+}
+
+/// A cell's mesh in numbers: its volume, smallest and mean scaled Jacobian and largest edge
+/// ratio.
+fn cell_quality(model: &Model, body: &str) -> Value {
+    let (mut volume, mut min, mut sum, mut n, mut ratio) = (0.0, f64::INFINITY, 0.0, 0usize, None::<f64>);
+    for label in model.body_elements(body) {
+        let Some(e) = model.element(label) else { continue };
+        let xyz: Vec<[f64; 3]> = e.nodes.iter().filter_map(|&l| model.node(l).map(|x| x.xyz)).collect();
+        let Ok(q) = fieldcraft_mesh::quality::element_quality(e.kind, &xyz) else { continue };
+        volume += q.size;
+        if let Some(r) = q.get(fieldcraft_mesh::quality::Metric::EdgeRatio) {
+            ratio = Some(ratio.map_or(r, |x| x.max(r)));
+        }
+        if let Some(sj) = q.get(fieldcraft_mesh::quality::Metric::ScaledJacobian) {
+            min = min.min(sj);
+            sum += sj;
+            n += 1;
+        }
+    }
+    let min = if n > 0 { Some(min) } else { None };
+    json!({"volume": volume, "min_scaled_jacobian": min, "mean_scaled_jacobian": if n > 0 { Some(sum / n as f64) } else { None }, "max_edge_ratio": ratio})
+}
+
 /// One side of an interface: a cell's element faces on one side of a partition.
 struct Side {
    body: String,
@@ -268,54 +519,160 @@ fn sides(model: &Model, cells: &[String]) -> BTreeMap<String, [Vec<Side>; 2]> {

 /// Join the cells across every partition: merge where the two sides match node for node, tie
 /// where they do not. Returns the interfaces.
-fn join(model: &mut Model, cells: &[String], tol: f64) -> Result<Vec<Value>> {
+///
+/// Ties go one way between any two cells, by a fixed order of the cells (hex before tet, then by
+/// name; the earlier one is the main side), so no two ties hold one interface both ways, and
+/// each cell's tied cut faces make one tie, `tie_<cell>` (its secondary surface; the main one is
+/// the facing cells' cut faces), so a node where two of them meet is a secondary node once.
+/// The ties of an earlier run on these cells are replaced.
+fn join(model: &mut Model, cells: &[String], tet: &BTreeSet<String>, tol: f64) -> Result<Vec<Value>> {
+    remove_cut_ties(model, cells)?;
+    let rank = |cell: &str| (tet.contains(cell), cell.to_string());
    let mut out = Vec::new();
+    // Per secondary cell: its cut faces and the facing cells' ones, as (body, face).
+    let mut tied: BTreeMap<String, (BTreeSet<(String, String)>, BTreeSet<(String, String)>)> = BTreeMap::new();
+    let mut tied_pairs: Vec<Value> = Vec::new();
    for (partition, [a_sides, b_sides]) in sides(model, cells) {
-        let mut k = 0;
        for a in &a_sides {
            for b in &b_sides {
-                let overlap = (0..3).all(|i| a.lo[i] <= b.hi[i] + tol && b.lo[i] <= a.hi[i] + tol);
-                if !overlap {
+                // Faces on one plane overlap when their boxes share an area, not just an edge.
+                let shared = (0..3).filter(|&i| a.lo[i].max(b.lo[i]) < a.hi[i].min(b.hi[i]) - tol).count();
+                let touching = (0..3).all(|i| a.lo[i] <= b.hi[i] + tol && b.lo[i] <= a.hi[i] + tol);
+                if !(touching && shared >= 2) {
                    continue;
                }
-                k += 1;
-                let matched = matching(model, a, b, tol);
-                if let Some(map) = matched {
+                if let Some(map) = matching(model, a, b, tol) {
                    let count = map.len();
                    model.merge_nodes(&map)?;
                    out.push(json!({"partition": partition, "cells": [a.body, b.body], "joined": "merged", "nodes": count}));
-                } else {
-                    let name = format!("tie_{partition}_{k}");
-                    let (main, secondary) = if a.nodes.len() <= b.nodes.len() { (a, b) } else { (b, a) };
-                    let set = |side: &Side| -> Result<Set> { Ok(Set::of_geometry(vec![GeometryRef::face(side.body.as_str(), side.face.as_str())?])) };
-                    let (main_set, secondary_set) = (format!("{name}_main"), format!("{name}_secondary"));
-                    for (n, side) in [(&main_set, main), (&secondary_set, secondary)] {
-                        if model.set(n).is_some() {
-                            model.replace_set(n, set(side)?)?;
-                        } else {
-                            model.add_set(n, set(side)?)?;
-                        }
-                    }
-                    if model.tie(&name).is_some() {
-                        model.remove_tie(&name)?;
-                    }
-                    model.add_tie(&name, Tie::new(&main_set, &secondary_set))?;
-                    out.push(json!({
-                        "partition": partition,
-                        "cells": [a.body, b.body],
-                        "joined": "tied",
-                        "tie": name,
-                        "main": main.body,
-                        "secondary": secondary.body,
-                        "faces": [a.faces.len(), b.faces.len()],
-                    }));
+                    continue;
                }
+                let (main, secondary) = if rank(&a.body) <= rank(&b.body) { (a, b) } else { (b, a) };
+                let entry = tied.entry(secondary.body.clone()).or_default();
+                entry.0.insert((secondary.body.clone(), secondary.face.clone()));
+                entry.1.insert((main.body.clone(), main.face.clone()));
+                tied_pairs.push(json!({
+                    "partition": partition,
+                    "cells": [a.body, b.body],
+                    "joined": "tied",
+                    "main": main.body,
+                    "secondary": secondary.body,
+                    "faces": [a.faces.len(), b.faces.len()],
+                }));
            }
        }
    }
+    let mut names: BTreeMap<String, String> = BTreeMap::new();
+    for (cell, (own, facing)) in tied {
+        let base = tie_name(&cell);
+        let mut name = base.clone();
+        let mut k = 1;
+        while model.tie(&name).is_some() || model.set(&format!("{name}_main")).is_some() || model.set(&format!("{name}_secondary")).is_some() {
+            k += 1;
+            name = format!("{base}_{k}");
+        }
+        let set = |faces: &BTreeSet<(String, String)>| -> Result<Set> {
+            Ok(Set::of_geometry(faces.iter().map(|(b, f)| GeometryRef::face(b.as_str(), f.as_str())).collect::<fieldcraft_model::Result<_>>()?))
+        };
+        let (main_set, secondary_set) = (format!("{name}_main"), format!("{name}_secondary"));
+        model.add_set(&main_set, set(&facing)?)?;
+        model.add_set(&secondary_set, set(&own)?)?;
+        model.add_tie(&name, Tie::new(&main_set, &secondary_set))?;
+        names.insert(cell, name);
+    }
+    for mut pair in tied_pairs {
+        let name = pair.get("secondary").and_then(Value::as_str).and_then(|c| names.get(c)).cloned();
+        if let (Some(o), Some(name)) = (pair.as_object_mut(), name) {
+            o.insert("tie".into(), json!(name));
+        }
+        out.push(pair);
+    }
    Ok(out)
 }

+/// Give every tied interface between cells of one design body its reason (`why`), from the
+/// cells' reports (#396): a cell meshed with tet (and why auto fell back), the reason the body's
+/// cells did not sweep together, or a cell whose method does not sweep with the others; so an
+/// agent knows which cut or method to change for a conforming mesh.
+fn explain_ties(design: &fieldcraft_geometry::Design, report: &[Value], interfaces: &mut [Value]) {
+    let info = |cell: &str| report.iter().find(|r| r.get("body").and_then(Value::as_str) == Some(cell));
+    let text = |r: Option<&Value>, key: &str| r.and_then(|r| r.get(key)).and_then(Value::as_str).map(String::from);
+    for interface in interfaces.iter_mut() {
+        if interface.get("joined").and_then(Value::as_str) != Some("tied") {
+            continue;
+        }
+        let cells: Vec<String> = interface
+            .get("cells")
+            .and_then(Value::as_array)
+            .map(|c| c.iter().filter_map(Value::as_str).map(String::from).collect())
+            .unwrap_or_default();
+        let [a, b] = cells.as_slice() else { continue };
+        let Some(source) = design.source_of(a).filter(|s| design.source_of(b) == Some(*s)) else { continue };
+        let mut why: Vec<String> = Vec::new();
+        for cell in [a, b] {
+            let r = info(cell);
+            if text(r, "kind").is_some_and(|k| k.starts_with("tet")) {
+                why.push(match text(r, "why") {
+                    Some(w) => format!("`{cell}` is meshed with tet: {w}"),
+                    None => format!("`{cell}` is meshed with tet"),
+                });
+            }
+        }
+        if why.is_empty() {
+            let not_together = [a, b].into_iter().find_map(|c| text(info(c), "not_swept_together"));
+            let alone = [a, b].into_iter().find(|c| text(info(c), "swept_together").is_none() && text(info(c), "not_swept_together").is_none());
+            if let Some(w) = not_together {
+                why.push(format!("the cells of `{source}` do not sweep together ({w}), so each was meshed alone with its own divisions"));
+            } else if let Some(c) = alone {
+                let method = text(info(c), "method").unwrap_or_default();
+                why.push(format!("`{c}` is meshed alone (method `{method}`), not swept with the other cells of `{source}`"));
+            } else {
+                why.push(format!("the element faces of `{a}` and `{b}` do not match node for node"));
+            }
+        }
+        if let Some(o) = interface.as_object_mut() {
+            o.insert("why".into(), json!(why.join("; ")));
+        }
+    }
+}
+
+/// The name of the tie that holds `cell`'s tied cut faces.
+fn tie_name(cell: &str) -> String {
+    let name = format!("tie_{cell}");
+    fieldcraft_model::suggest_name(&name).unwrap_or(name)
+}
+
+/// Remove the ties an earlier run of mesh.cells made on `cells` (and their two sets): ties
+/// between sets `<tie>_main` and `<tie>_secondary` that hold only cut faces of these cells.
+fn remove_cut_ties(model: &mut Model, cells: &[String]) -> Result<()> {
+    let cut_faces_of_cells = |set: &str| {
+        model.set(set).is_some_and(|s| {
+            !s.geometry.is_empty()
+                && s.nodes.is_empty()
+                && s.elements.is_empty()
+                && s.faces.is_empty()
+                && s.edges.is_empty()
+                && s.geometry.iter().all(|g| cells.contains(&g.body) && matches!(&g.entity, Entity::Face(f) if f.starts_with("partition:")))
+        })
+    };
+    let stale: Vec<(String, String, String)> = model
+        .ties()
+        .iter()
+        .filter(|(n, t)| t.main == format!("{n}_main") && t.secondary == format!("{n}_secondary"))
+        .filter(|(_, t)| cut_faces_of_cells(&t.main) && cut_faces_of_cells(&t.secondary))
+        .map(|(n, t)| (n.clone(), t.main.clone(), t.secondary.clone()))
+        .collect();
+    for (tie, main, secondary) in stale {
+        model.remove_tie(&tie)?;
+        for set in [main, secondary] {
+            if model.set_users(&set).is_empty() {
+                model.remove_set(&set)?;
+            }
+        }
+    }
+    Ok(())
+}
+
 /// When the two sides' nodes coincide one to one (within `tol`) and their faces are the same
 /// in number, the merge: each node of side `b` to the node of side `a` at its place (or the other
 /// way round, so the lower label survives).
@@ -349,14 +706,16 @@ mod tests {
    #[test]
    fn hex_and_tet_cells_are_tied_and_matching_hex_cells_merged() {
        let (_dir, mut s) = cut_plate();
-        // A tet cell next to a hex cell: tied, main the coarser side.
-        let r = s.execute("mesh.cells", &json!({"methods": {"Body1/a": "tet", "Body1/b": "mapped"}, "size": 2.5})).unwrap();
+        // A tet cell next to a hex cell: tied, the hex cell main.
+        let r = s.execute("mesh.cells", &json!({"methods": {"Body1/a": "tet", "Body1/b": "mapped"}, "size": 2.5, "transition": "tie"})).unwrap();
        assert_eq!(r["cells"][0]["kind"], "tet4", "{r}");
        assert_eq!(r["cells"][1]["kind"], "hex8", "{r}");
        let i = &r["interfaces"][0];
        assert_eq!(i["joined"], "tied", "{r}");
+        assert!(i["why"].as_str().is_some_and(|w| w.contains("`Body1/a` is meshed with tet")), "{r}");
        assert_eq!(s.model.ties().len(), 1);
-        for set in ["tie_P_1_main", "tie_P_1_secondary"] {
+        assert_eq!((i["main"].as_str(), i["secondary"].as_str(), i["tie"].as_str()), (Some("Body1/b"), Some("Body1/a"), Some("tie_Body1_a")), "{r}");
+        for set in ["tie_Body1_a_main", "tie_Body1_a_secondary"] {
            assert!(s.model.resolve_set(set).unwrap().faces.len() > 4, "{set}");
        }
        // Both cells hex at one size: the plane faces match node for node and merge.
@@ -367,10 +726,37 @@ mod tests {
        let separate = r["cells"].as_array().unwrap().iter().map(|c| c["nodes"].as_u64().unwrap()).sum::<u64>();
        assert_eq!(r["nodes"].as_u64().unwrap() + i["nodes"].as_u64().unwrap(), separate, "{r}");
        // Rerunning replaces the tie it made rather than adding another.
-        s.execute("mesh.cells", &json!({"methods": {"Body1/a": "tet"}, "size": 2.5})).unwrap();
+        s.execute("mesh.cells", &json!({"methods": {"Body1/a": "tet"}, "size": 2.5, "transition": "tie"})).unwrap();
        assert_eq!(s.model.ties().len(), 1);
    }

+    /// A tie between cells of one design body says why they were not conforming (#396): the
+    /// reason the body's cells did not sweep together, or the cell meshed alone by its method.
+    #[test]
+    fn ties_inside_one_body_say_why() {
+        let (_dir, s) = cut_plate();
+        let design = s.design.clone().unwrap();
+        let tied = || vec![json!({"cells": ["Body1/a", "Body1/b"], "joined": "tied"}), json!({"cells": ["Body1/a", "Body1/b"], "joined": "merged"})];
+        let mut interfaces = tied();
+        let report = [
+            json!({"body": "Body1/a", "kind": "hex8", "method": "extrude", "not_swept_together": "extrude: the levels differ"}),
+            json!({"body": "Body1/b", "kind": "hex8", "method": "extrude", "not_swept_together": "extrude: the levels differ"}),
+        ];
+        explain_ties(&design, &report, &mut interfaces);
+        assert_eq!(
+            interfaces[0]["why"],
+            "the cells of `Body1` do not sweep together (extrude: the levels differ), so each was meshed alone with its own divisions"
+        );
+        assert!(interfaces[1].get("why").is_none());
+        let mut interfaces = tied();
+        let report = [
+            json!({"body": "Body1/a", "kind": "hex8", "method": "mapped"}),
+            json!({"body": "Body1/b", "kind": "hex8", "method": "extrude", "swept_together": "Body1"}),
+        ];
+        explain_ties(&design, &report, &mut interfaces);
+        assert_eq!(interfaces[0]["why"], "`Body1/a` is meshed alone (method `mapped`), not swept with the other cells of `Body1`");
+    }
+
    /// The half crank arm (cut on its symmetry plane only) has no cell that maps or sweeps as
    /// the design gives it; the extrusion decomposes its cross-section into blocks itself, alike
    /// through mesh.hex.generate (auto) and mesh.cells, with no seeds.
@@ -423,11 +809,10 @@ mod tests {
    }

    /// A 40 × 10 × 10 bar in uniaxial tension, cut in the middle: one half hex, the other tet,
-    /// tied. With ν = 0, symmetry conditions on three faces and the end load spread by consistent
-    /// weights, the stress is uniform, which both elements and the dual mortar tie carry exactly:
-    /// the end moves F L / (E A).
-    #[test]
-    fn a_tied_hex_tet_bar_in_tension_stretches_as_the_formula_says() {
+    /// joined by `transition` (`joined` in the reply). With ν = 0, symmetry conditions on three
+    /// faces and the end load spread by consistent weights, the stress is uniform, which the
+    /// elements, the pyramids and the dual mortar tie all carry exactly: the end moves F L / (E A).
+    fn hex_tet_bar_in_tension(transition: &str, joined: &str) -> Session {
        let commands = json!({"commands": [
            {"command": "solid.box", "params": {"length": 40, "width": 10, "height": 10, "body_name": "Bar"}},
        ]});
@@ -447,8 +832,8 @@ mod tests {
        point[axis] = mid;
        s.execute("geometry.datum", &json!({"name": "Mid", "by": {"type": "point_normal", "point": point, "normal": normal}})).unwrap();
        s.execute("geometry.partition", &json!({"name": "Cut", "datum": "Mid"})).unwrap();
-        let r = s.execute("mesh.cells", &json!({"methods": {"Bar/a": "mapped", "Bar/b": "tet"}, "size": 2.5})).unwrap();
-        assert_eq!(r["interfaces"][0]["joined"], "tied", "{r}");
+        let r = s.execute("mesh.cells", &json!({"methods": {"Bar/a": "mapped", "Bar/b": "tet"}, "size": 2.5, "transition": transition})).unwrap();
+        assert_eq!(r["interfaces"][0]["joined"], joined, "{r}");

        let m = &s.model;
        let on = |k: usize, v: f64| -> Vec<u32> { m.nodes().iter().filter(|(_, n)| (n.xyz[k] - v).abs() < 1e-9).map(|(l, _)| *l).collect() };
@@ -490,5 +875,118 @@ mod tests {
            let u = n["displacement"][axis].as_f64().unwrap();
            assert!((u - expected).abs() < 1e-6 * expected, "{u} vs {expected}: {n}");
        }
+        s
+    }
+
+    #[test]
+    fn a_tied_hex_tet_bar_in_tension_stretches_as_the_formula_says() {
+        let s = hex_tet_bar_in_tension("tie", "tied");
+        assert_eq!(s.model.ties().len(), 1);
+    }
+
+    /// Through pyramids the bar is one conforming mesh: no tie, no free faces inside, every
+    /// element valid.
+    #[test]
+    fn a_hex_tet_bar_joined_by_pyramids_is_conforming_and_stretches_as_the_formula_says() {
+        let mut s = hex_tet_bar_in_tension("pyramid", "pyramids");
+        assert!(s.model.ties().is_empty());
+        let kinds: BTreeSet<&str> = s.model.elements().values().map(|e| e.kind.name()).collect();
+        assert_eq!(kinds.into_iter().collect::<Vec<_>>(), ["hex8", "pyramid5", "tet4"]);
+        let d = s.execute("mesh.check.duplicates", &json!({})).unwrap();
+        assert_eq!(d["counts"], json!({"coincident": 0, "cracks": 0, "duplicate_elements": 0, "free_edges": 0}), "{d}");
+        let q = s.execute("mesh.quality", &json!({})).unwrap();
+        assert_eq!(q["invalid"]["count"], 0, "{q}");
+    }
+
+    /// A box cut by planes into cells, `methods` per cell, a heat source in every cell and
+    /// convection on its outer faces: the heat flows of the steady solve.
+    fn cut_box_heat(cuts: &[(&str, f64)], methods: Value, size: f64) -> (Value, Value) {
+        let commands = json!({"commands": [
+            {"command": "solid.box", "params": {"length": 30, "width": 20, "height": 10, "body_name": "Box"}},
+        ]});
+        let bytes = fieldcraft_geometry::script_design(&commands.to_string()).unwrap();
+        let (_dir, path) = crate::tests::design_file(&bytes);
+        let mut s = Session::default();
+        s.execute("geometry.open", &json!({"path": path})).unwrap();
+        for (i, (plane, offset)) in cuts.iter().enumerate() {
+            let name = format!("D{i}");
+            s.execute("geometry.datum", &json!({"name": name, "by": {"type": "offset", "plane": plane, "offset": offset}})).unwrap();
+            s.execute("geometry.partition", &json!({"name": format!("P{i}"), "datum": name})).unwrap();
+        }
+        let r = s.execute("mesh.cells", &json!({"methods": methods, "default": "hex", "size": size})).unwrap();
+        let bodies = s.execute("geometry.bodies", &json!({})).unwrap();
+        let outer: Vec<Value> = bodies
+            .as_array()
+            .unwrap()
+            .iter()
+            .flat_map(|b| {
+                b["faces"]
+                    .as_array()
+                    .unwrap()
+                    .iter()
+                    .filter(|f| !f["name"].as_str().unwrap().starts_with("partition:"))
+                    .map(|f| json!({"body": b["name"], "face": f["name"]}))
+                    .collect::<Vec<_>>()
+            })
+            .collect();
+        let script = json!([
+            {"command": "model.set.create", "params": {"name": "all", "elements": s.model.elements().keys().collect::<Vec<_>>()}},
+            {"command": "model.set.create", "params": {"name": "skin", "geometry": outer}},
+            {"command": "model.material.create", "params": {"name": "M", "elastic": {"type": "isotropic", "young": 1000, "poisson": 0.3}, "thermal": {"conductivity": 0.5}}},
+            {"command": "model.section.create", "params": {"name": "S", "set": "all", "material": "M", "kind": {"type": "solid"}}},
+            {"command": "model.load.create", "params": {"name": "Q", "type": "heat_source", "set": "all", "power": 1}},
+            {"command": "model.load.create", "params": {"name": "Air", "type": "convection", "set": "skin", "film": 0.01, "sink": 25}},
+            {"command": "model.step.create", "params": {"name": "Steady", "procedure": {"type": "heat_transfer"}, "loads": ["Q", "Air"]}},
+        ]);
+        s.run_script(&script).unwrap();
+        let h = s.execute("solve.heat", &json!({"step": "Steady"})).unwrap();
+        (r, h)
+    }
+
+    /// A tet cell among hex cells (#389, #288): the hex cells sweep together and share their
+    /// nodes, the tet cell is tied once (one tie for all its cut faces, the hex cells main), and
+    /// the heat balances to round-off.
+    #[test]
+    fn a_tet_cell_among_swept_hex_cells_is_tied_once_and_the_heat_balances() {
+        let (r, h) = cut_box_heat(&[("yz", 10.0), ("yz", 20.0), ("zx", 10.0)], json!({"Box/b/a/a": "tet"}), 2.5);
+        let interfaces = r["interfaces"].as_array().unwrap();
+        let tied: Vec<&Value> = interfaces.iter().filter(|i| i["joined"] == "tied").collect();
+        assert_eq!(tied.len(), 3, "{r}");
+        assert!(tied.iter().all(|i| i["secondary"] == "Box/b/a/a" && i["tie"] == "tie_Box_b_a_a"), "{r}");
+        assert!(tied.iter().all(|i| i["why"].as_str().is_some_and(|w| w.starts_with("`Box/b/a/a` is meshed with tet"))), "{r}");
+        let merged: Vec<&Value> = interfaces.iter().filter(|i| i["joined"] == "merged").collect();
+        assert_eq!(merged.len(), 4, "{r}");
+        // Box/a/a and Box/a/b meet across y = 10, the third cut.
+        assert!(merged.iter().any(|i| i["cells"] == json!(["Box/a/a", "Box/a/b"]) && i["partition"] == "P2"), "{r}");
+        let flows = &h["heat_flows"];
+        let supplied = flows["loads"].as_array().unwrap().iter().find(|l| l["name"] == "Q").unwrap()["heat"].as_f64().unwrap();
+        assert!(flows["imbalance"].as_f64().unwrap().abs() < 1e-9 * supplied, "{flows}");
+        assert!(h["min_temperature"]["value"].as_f64().unwrap() > 25.0, "{h}");
+    }
+
+    /// Cells cut from one box by planes, one of them (`y = 10`) cutting only the cell left of
+    /// `x = 10`, so a cut ends on another (a T-junction): with no seeds the cells sweep together
+    /// and every interface merges node for node (#288), and the mesh fills the box.
+    #[test]
+    fn cells_of_a_body_sweep_together_and_merge_without_seeds() {
+        let (_dir, mut s) = super::super::datum::tests::scripted(json!([
+            {"command": "solid.box", "params": {"length": 30, "width": 20, "height": 10, "corner": [0, 0, 0], "body_name": "Box"}},
+        ]));
+        super::super::datum::tests::cut_at(&mut s, &[(0, 10.0), (0, 21.0)]);
+        s.execute("geometry.datum", &json!({"name": "Y", "by": {"type": "offset", "plane": "zx", "offset": 7.5}})).unwrap();
+        s.execute("geometry.partition", &json!({"name": "PY", "datum": "Y", "bodies": ["Box/a"]})).unwrap();
+        let r = s.execute("mesh.cells", &json!({"default": "auto", "size": 2.0})).unwrap();
+        let cells = r["cells"].as_array().unwrap();
+        assert_eq!(cells.len(), 4, "{r}");
+        assert!(cells.iter().all(|c| c["swept_together"] == "Box" && c["kind"] == "hex8"), "{r}");
+        let interfaces = r["interfaces"].as_array().unwrap();
+        assert_eq!(interfaces.len(), 4, "{r}");
+        assert!(interfaces.iter().all(|i| i["joined"] == "merged"), "{r}");
+        assert!(s.model.ties().is_empty());
+        let q = s.execute("mesh.quality", &json!({})).unwrap();
+        let volume = q["volume"].as_f64().unwrap();
+        assert!((volume - 6000.0).abs() < 1e-6, "{q}");
+        let d = s.execute("mesh.check.duplicates", &json!({})).unwrap();
+        assert_eq!((d["counts"]["coincident"].as_u64(), d["counts"]["cracks"].as_u64()), (Some(0), Some(0)), "{d}");
    }
 }
@@ -0,0 +1,172 @@
+//! Pyramid transitions between a tet cell and the hex cells across its partitions (#439).
+//!
+//! The tet cell is meshed after the hex cells: its cut faces that face hex cells are replaced by
+//! a pyramid on every hex element face there ([`fieldcraft_mesh::transition`]), the tetrahedra
+//! fill the rest and keep the pyramids' sides, and the pyramids join the hex nodes to the tet
+//! nodes. The mesh is conforming across the cut, so no tie is needed there.
+
+use std::collections::{BTreeMap, BTreeSet};
+
+use fieldcraft_mesh::cdt::{CdtOptions, tetrahedralize};
+use fieldcraft_mesh::surface::BoundarySurface;
+use fieldcraft_mesh::tet::{QualityMesh, QualityOptions, quality_mesh};
+use fieldcraft_mesh::transition::{Transition, apex_points, pyramid_surface};
+use fieldcraft_model::{ElementKind, GeometryRef, Model};
+use serde_json::{Value, json};
+
+use super::super::hex::Input;
+use super::super::mesh::{BodyTets, add_tets, analytic_surfaces};
+use crate::{EngineError, Result};
+
+/// A tet cell meshed against the pyramids on its hex neighbours' faces.
+pub(super) struct Pyramids {
+    pub(super) tets: BodyTets,
+    transition: Transition,
+    /// Each pyramid's base: the hex nodes of its face, oriented into the tet cell.
+    bases: Vec<[u32; 4]>,
+    /// The interfaces it makes (reply entries).
+    pub(super) interfaces: Vec<Value>,
+}
+
+/// The base name of a cut face (`partition:P:a` of `partition:P:a#1`): its partition and side.
+fn cut_of(name: &str) -> Option<(&str, usize)> {
+    let base = name.split_once('#').map_or(name, |(b, _)| b);
+    let (partition, side) = base.strip_prefix("partition:")?.rsplit_once(':')?;
+    Some((partition, usize::from(side == "b")))
+}
+
+/// Mesh tet cell `input` with pyramids on the faces of the hex cells `hex` (already in `model`)
+/// across its cut faces. `Ok(Err(why))` when there is no such face or the transition cannot be
+/// built (the caller meshes the cell plainly and ties it); limits and a cancel are errors.
+pub(super) fn mesh_with_pyramids(
+    design: &fieldcraft_geometry::Design,
+    model: &Model,
+    p: &Value,
+    input: &Input,
+    hex: &[String],
+    cdt: &CdtOptions,
+    options: &QualityOptions,
+) -> Result<std::result::Result<Pyramids, String>> {
+    // The hex element faces across each of the cell's cut faces.
+    let sides = super::sides(model, hex);
+    let mut cut: Vec<u32> = Vec::new();
+    let mut quads: Vec<[u32; 4]> = Vec::new();
+    let mut interfaces = Vec::new();
+    let mut seen: BTreeSet<(String, String)> = BTreeSet::new();
+    for (i, name) in input.face_names.iter().enumerate() {
+        let Some((partition, side)) = cut_of(name) else { continue };
+        let Some(across) = sides.get(partition).and_then(|s| s.get(1 - side)) else { continue };
+        if across.is_empty() {
+            continue;
+        }
+        cut.push(i as u32);
+        for other in across {
+            if !seen.insert((partition.to_string(), other.body.clone())) {
+                continue;
+            }
+            for f in &other.faces {
+                let nodes = model.face_nodes(*f).unwrap_or_default();
+                let Ok(q) = <[u32; 4]>::try_from(nodes.as_slice()) else {
+                    return Ok(Err(format!("`{}` has quadratic or non-quadrilateral faces on the cut; pyramid transitions are linear", other.body)));
+                };
+                quads.push(q);
+            }
+            interfaces.push((partition.to_string(), other.body.clone(), other.faces.len()));
+        }
+    }
+    if quads.is_empty() {
+        return Ok(Err("no hex cell faces it across a partition".into()));
+    }
+    // The hex faces must cover the cut faces exactly (a cut shared with a tet cell, or a hex
+    // cell larger than this one, is tied instead).
+    let xyz = |n: u32| model.node(n).map(|x| x.xyz).unwrap_or([f64::NAN; 3]);
+    let positions: Vec<[[f64; 3]; 4]> = quads.iter().map(|q| q.map(xyz)).collect();
+    let quad_area: f64 = positions.iter().map(|q| 0.5 * norm(cross(sub(q[2], q[0]), sub(q[3], q[1])))).sum();
+    let m = &input.mesh;
+    let cut_area: f64 = m
+        .triangles
+        .iter()
+        .zip(&m.tri_face)
+        .filter(|(_, f)| cut.contains(f))
+        .map(|(t, _)| {
+            let c = t.map(|v| m.positions.get(v as usize).copied().unwrap_or([f64::NAN; 3]));
+            0.5 * norm(cross(sub(c[1], c[0]), sub(c[2], c[0])))
+        })
+        .sum();
+    if !((quad_area - cut_area).abs() <= 1e-3 * cut_area) {
+        return Ok(Err(format!("the hex cells' faces ({quad_area:.6} mm²) do not cover its cut faces ({cut_area:.6} mm²)")));
+    }
+    let tag = u32::try_from(input.face_names.len()).map_err(|_| EngineError::Params("too many faces".into()))?;
+    let welding = super::super::mesh::surface_options(p, m)?;
+    let built = || -> fieldcraft_mesh::Result<(QualityMesh, Transition, usize, usize, f64)> {
+        let surface = BoundarySurface::new(&m.positions, &m.triangles, &m.tri_face, &welding)?;
+        let t = pyramid_surface(&surface, &cut, &positions, tag)?;
+        // Already welded: nothing more merges.
+        let exact = fieldcraft_mesh::surface::SurfaceOptions { weld_tolerance: 0.0, weld_distance: 0.0, ..welding };
+        let region = BoundarySurface::new(&t.positions, &t.triangles, &t.tri_face, &exact)?;
+        let tets = tetrahedralize(&region, cdt)?;
+        let mut analytic = design.body(&input.name).map(analytic_surfaces).unwrap_or_default();
+        analytic.resize(tag as usize, None);
+        analytic.push(None);
+        let o = QualityOptions { seeds: input.seeds.clone(), frozen_faces: vec![tag], ..options.clone() };
+        let mesh = quality_mesh(&region, &tets, analytic, &o)?;
+        Ok((mesh, t, tets.steiner.len(), tets.stats.cavities, region.volume()))
+    };
+    let (mesh, transition, steiner, cavities, volume) = match built() {
+        Ok(x) => x,
+        Err(fieldcraft_mesh::Error::Model(fieldcraft_model::Error::Cancelled)) => return Err(EngineError::Model(fieldcraft_model::Error::Cancelled)),
+        Err(e @ fieldcraft_mesh::Error::Limit(_)) => return Err(EngineError::Params(e.to_string())),
+        Err(e) => return Ok(Err(e.to_string())),
+    };
+    if let Err(e) = apex_points(&mesh, &transition) {
+        return Ok(Err(e.to_string()));
+    }
+    let tets = BodyTets::new(input.name.clone(), input.face_names.clone(), mesh, steiner, cavities, volume);
+    let interfaces = interfaces
+        .into_iter()
+        .map(|(partition, other, faces)| json!({"partition": partition, "cells": [other, input.name], "joined": "pyramids", "pyramids": faces}))
+        .collect();
+    Ok(Ok(Pyramids { tets, transition, bases: quads, interfaces }))
+}
+
+/// Add the cell's tetrahedra and pyramids to `model`: the tetrahedra's nodes on the hex faces
+/// are the hex nodes, the pyramids join them to the apexes.
+pub(super) fn add(model: &mut Model, mut c: Pyramids) -> Result<(usize, usize)> {
+    let tag = c.tets.face_names.len() as u32;
+    let apexes = apex_points(&c.tets.mesh, &c.transition).map_err(|e| EngineError::Params(e.to_string()))?;
+    // The pyramid sides are inside the part: no geometry face.
+    c.tets.mesh.boundary.retain(|b| b.face != tag);
+    let (first_node, _) = add_tets(model, &c.tets.name, &c.tets.face_names, &c.tets.mesh)?;
+    // The tet mesh keeps the hex nodes' coordinates exactly: merge its copies into them.
+    let hex: BTreeMap<[u64; 3], u32> = c.bases.iter().flatten().filter_map(|&n| model.node(n).map(|x| (x.xyz.map(f64::to_bits), n))).collect();
+    let mut merge = BTreeMap::new();
+    for (i, x) in c.tets.mesh.points.iter().enumerate() {
+        if let Some(&h) = hex.get(&x.map(f64::to_bits)) {
+            merge.insert(first_node + i as u32, h);
+        }
+    }
+    let shared = merge.len();
+    model.merge_nodes(&merge)?;
+    let (_, first) = crate::cmd::fresh_labels(model, 0, c.bases.len())?;
+    let body = model.geometry_tag(&GeometryRef::body(c.tets.name.as_str())?)?;
+    for (k, (base, apex)) in c.bases.iter().zip(apexes).enumerate() {
+        let label = first + k as u32;
+        let mut nodes = base.to_vec();
+        nodes.push(first_node + apex);
+        model.set_element(label, ElementKind::Pyramid5, nodes)?;
+        model.tag_element(label, body)?;
+    }
+    Ok((c.tets.mesh.elements.len() + c.bases.len(), c.tets.mesh.points.len() - shared))
+}
+
+fn sub(a: [f64; 3], b: [f64; 3]) -> [f64; 3] {
+    [a[0] - b[0], a[1] - b[1], a[2] - b[2]]
+}
+
+fn cross(a: [f64; 3], b: [f64; 3]) -> [f64; 3] {
+    [a[1] * b[2] - a[2] * b[1], a[2] * b[0] - a[0] * b[2], a[0] * b[1] - a[1] * b[0]]
+}
+
+fn norm(a: [f64; 3]) -> f64 {
+    (a[0] * a[0] + a[1] * a[1] + a[2] * a[2]).sqrt()
+}
@@ -1,5 +1,7 @@
 //! `interaction.contact.*`: contact definitions (pairs of surfaces, general contact) and the
-//! search for surfaces that touch; `interaction.tie*`: ties between non-matching meshes.
+//! search for surfaces that touch; `interaction.tie*`: ties between non-matching meshes;
+//! `interaction.rigid_wall*`: rigid walls, which belong to an explicit dynamics step (its
+//! `rigid_walls`, also edited in the step's form).
 //!
 //! A contact's surfaces are sets of element faces, or of element edges in a 2D model
 //! ([`fieldcraft_model::contact`]). The commands
@@ -16,7 +18,7 @@ use crate::schema::ProblemKind;
 use std::collections::BTreeMap;

 use fieldcraft_fem::contact::{Grid, bounds, closest_point};
-use fieldcraft_model::{Contact, ContactSurfaces, ElementFace, Friction, InitialPenetration, Model, Set, Tie};
+use fieldcraft_model::{Contact, ContactSurfaces, ElementFace, Friction, InitialPenetration, Model, Procedure, RigidWall, Set, Step, Tie};
 use serde_json::{Value, json};

 use super::{name, opt};
@@ -38,6 +40,88 @@ fn text<'a>(p: &'a Value, key: &str) -> Result<&'a str> {
    p.get(key).and_then(Value::as_str).ok_or_else(|| EngineError::param(key, ProblemKind::NotAName))
 }

+pub const RIGID_WALL: CommandSpec = CommandSpec {
+    id: "interaction.rigid_wall",
+    label: "Rigid Wall",
+    params: r#"{"step": "Impact" (an explicit dynamics step; default: the model's only one), "set": "front" (the nodes the wall stops), "point": [x, y, z] (on the wall), "normal": [nx, ny, nz] (toward the side the nodes stay on), "friction": {"static": 0.3, "kinetic": 0.2, "decay": 10} (Coulomb; default frictionless)} — a fixed rigid plane the set's nodes cannot pass, added to the step's rigid walls (the same list as model.step.create's `rigid_walls`). Replies the step and the wall's index in it"#,
+    form: Some(super::forms::RIGID_WALL),
+    kind: CommandKind::Model,
+    requires: &[Requirement::Step, Requirement::Set],
+    run: rigid_wall,
+};
+
+pub const RIGID_WALL_DELETE: CommandSpec = CommandSpec {
+    id: "interaction.rigid_wall.delete",
+    label: "Delete Rigid Wall",
+    params: r#"{"step": "Impact", "index": 0} — removes a rigid wall from an explicit dynamics step (its index in the step's `rigid_walls`, from 0)"#,
+    form: Some(super::forms::RIGID_WALL_DELETE),
+    kind: CommandKind::Model,
+    requires: &[Requirement::Step],
+    run: rigid_wall_delete,
+};
+
+/// The explicit dynamics step `step` names, or the model's only one when it names none.
+fn explicit_step(m: &Model, p: &Value) -> Result<Step> {
+    let explicit = |s: &&Step| matches!(s.procedure, Procedure::ExplicitDynamic(_));
+    let step = match p.get("step") {
+        None | Some(Value::Null) => {
+            let mut all = m.steps().iter().filter(explicit);
+            match (all.next(), all.next()) {
+                (Some(s), None) => s,
+                (None, _) => {
+                    return Err(EngineError::Params(
+                        "the model has no explicit dynamics step, where rigid walls act: create one (Steps › Step, Dynamic, explicit)".into(),
+                    ));
+                }
+                (Some(_), Some(_)) => {
+                    return Err(EngineError::param("step", ProblemKind::Invalid("name the explicit dynamics step: the model has several".into())));
+                }
+            }
+        }
+        Some(_) => {
+            let n = text(p, "step")?;
+            let s = m.steps().iter().find(|s| s.name == n).ok_or_else(|| EngineError::Params(format!("no step `{n}`")))?;
+            if !explicit(&s) {
+                return Err(EngineError::Params(format!("step `{n}` is not an explicit dynamics step: rigid walls act only there")));
+            }
+            s
+        }
+    };
+    Ok(step.clone())
+}
+
+fn rigid_wall(s: &mut Session, p: &Value) -> Result<Value> {
+    let mut step = explicit_step(&s.model, p)?;
+    let set = text(p, "set")?.to_string();
+    if s.model.set(&set).is_none() {
+        return Err(EngineError::Params(format!("no set `{set}`")));
+    }
+    let wall = RigidWall {
+        set,
+        point: super::req(p, "point")?,
+        normal: super::req(p, "normal")?,
+        friction: opt::<Friction>(p, "friction")?.unwrap_or(Friction::NONE),
+    };
+    let Procedure::ExplicitDynamic(e) = &mut step.procedure else { return Err(EngineError::Params("not an explicit dynamics step".into())) };
+    e.rigid_walls.push(wall);
+    let index = e.rigid_walls.len() - 1;
+    let name = step.name.clone();
+    s.model.replace_step(step)?;
+    Ok(json!({"step": name, "index": index}))
+}
+
+fn rigid_wall_delete(s: &mut Session, p: &Value) -> Result<Value> {
+    let mut step = explicit_step(&s.model, p)?;
+    let index: usize = super::req(p, "index")?;
+    let Procedure::ExplicitDynamic(e) = &mut step.procedure else { return Err(EngineError::Params("not an explicit dynamics step".into())) };
+    if index >= e.rigid_walls.len() {
+        return Err(EngineError::param("index", ProblemKind::Invalid(format!("step `{}` has {} rigid walls", step.name, e.rigid_walls.len()))));
+    }
+    e.rigid_walls.remove(index);
+    s.model.replace_step(step)?;
+    Ok(Value::Null)
+}
+
 pub const PAIR: CommandSpec = CommandSpec {
    id: "interaction.contact.pair",
    label: "Contact Pair",
@@ -322,6 +406,36 @@ fn find(s: &mut Session, p: &Value) -> Result<Value> {
 mod tests {
    use super::*;

+    /// Rigid walls go into the explicit step (the model's only one, or the one named) and come
+    /// out by index; a model without an explicit step, or a step of another kind, is refused.
+    #[test]
+    fn rigid_walls_belong_to_the_explicit_step() {
+        let mut s = Session::default();
+        super::super::define::tests::defined_bar(&mut s);
+        let wall = json!({"set": "end", "point": [3, 0, 0], "normal": [-1, 0, 0], "friction": {"static": 0.2}});
+        assert!(s.execute("interaction.rigid_wall", &wall).is_err(), "no explicit step yet");
+        let mut on_bend = wall.clone();
+        on_bend["step"] = json!("Bend");
+        assert!(s.execute("interaction.rigid_wall", &on_bend).is_err(), "a static step");
+        s.execute("model.step.create", &json!({"name": "Hit", "procedure": {"type": "explicit_dynamic", "end_time": 1e-4}})).unwrap();
+        let r = s.execute("interaction.rigid_wall", &wall).unwrap();
+        assert_eq!(r, json!({"step": "Hit", "index": 0}));
+        let walls = |s: &Session| match &s.model.step("Hit").unwrap().procedure {
+            Procedure::ExplicitDynamic(e) => e.rigid_walls.clone(),
+            _ => panic!(),
+        };
+        assert_eq!(walls(&s).len(), 1);
+        assert_eq!(walls(&s)[0].set, "end");
+        for bad in [json!({"set": "nope", "point": [0, 0, 0], "normal": [1, 0, 0]}), json!({"set": "end", "point": [0, 0, 0], "normal": [0, 0, 0]})] {
+            assert!(s.execute("interaction.rigid_wall", &bad).is_err(), "{bad}");
+        }
+        assert!(s.execute("interaction.rigid_wall.delete", &json!({"step": "Hit", "index": 1})).is_err());
+        s.execute("interaction.rigid_wall.delete", &json!({"step": "Hit", "index": 0})).unwrap();
+        assert!(walls(&s).is_empty());
+        s.execute("model.step.create", &json!({"name": "Hit2", "procedure": {"type": "explicit_dynamic", "end_time": 1e-4}})).unwrap();
+        assert!(s.execute("interaction.rigid_wall", &wall).is_err(), "two explicit steps: name one");
+    }
+
    /// Two unit cubes of 2×2×2 hex8 each, the second resting on the first (separate nodes), and
    /// a third cube far away.
    fn stacked(s: &mut Session) {
@@ -12,7 +12,7 @@
 use crate::schema::ProblemKind;
 use std::sync::Arc;

-use fieldcraft_geometry::{Cut, Design};
+use fieldcraft_geometry::{Cut, Design, Merge};
 use fieldcraft_io::{Item, ItemKind, MAX_HIDDEN};
 use fieldcraft_model::{Datum, Model, Partition};
 use serde::Deserialize;
@@ -44,7 +44,7 @@ pub const DATUM_AXIS: CommandSpec = CommandSpec {
 pub const DATUM_POINT: CommandSpec = CommandSpec {
    id: "geometry.datum.point",
    label: "Datum Point",
-    params: r#"{"name": "P1", "by": {"type": "coordinates", "point": [x, y, z]} | {"type": "vertex", "body": "Body1", "vertex": "v3"} | {"type": "edge", "body": "Body1", "edge": "F1:top|F2:side", "fraction"?: 0.5} | {"type": "face_centre", "body": "Body1", "face": "F2:top"} | {"type": "axis_plane", "axis": "Spindle", "plane": "Mid"}} — a named datum point, shown in the viewport as a small cross: at coordinates, at a vertex of the mesh (as its geometry tags name it), a fraction along an edge of the open design (0.5: its midpoint), at the area centre of a face of the open design, or where a datum axis crosses a datum plane. Datum planes and axes can be made through datum points"#,
+    params: r#"{"name": "P1", "by": {"type": "coordinates", "point": [x, y, z]} | {"type": "vertex", "body": "Body1", "vertex": "F1:top|F2:side:l1|F2:side:l2"} | {"type": "edge", "body": "Body1", "edge": "F1:top|F2:side", "fraction"?: 0.5} | {"type": "face_centre", "body": "Body1", "face": "F2:top"} | {"type": "axis_plane", "axis": "Spindle", "plane": "Mid"}} — a named datum point, shown in the viewport as a small cross: at coordinates, at a vertex of the open design (its persistent name, as geometry.bodies lists it and Select: Vertices picks it) or of the mesh (as its geometry tags name it), a fraction along an edge of the open design (0.5: its midpoint), at the area centre of a face of the open design, or where a datum axis crosses a datum plane. Datum planes and axes can be made through datum points"#,
    form: Some(super::forms::DATUM_POINT),
    kind: CommandKind::Model,
    requires: &[],
@@ -84,7 +84,7 @@ pub const DATUM_POINT_EDIT: CommandSpec = CommandSpec {
 pub const DATUM_DELETE: CommandSpec = CommandSpec {
    id: "geometry.datum.delete",
    label: "Delete Datum",
-    params: r#"{"name": "Mid", "cascade"?: false} — deletes a datum plane, axis or point; one a partition cuts by is refused (naming the partitions), unless `cascade` deletes those partitions too"#,
+    params: r#"{"name": "Mid", "cascade"?: false} — deletes a datum plane, axis or point; one a partition cuts by is refused (naming the partitions), unless `cascade` deletes those partitions too (their cells lose their meshes: `replaced`)"#,
    form: Some(super::forms::DATUM_DELETE),
    kind: CommandKind::Model,
    requires: &[Requirement::Datum],
@@ -94,17 +94,37 @@ pub const DATUM_DELETE: CommandSpec = CommandSpec {
 pub const PARTITION: CommandSpec = CommandSpec {
    id: "geometry.partition",
    label: "Partition",
-    params: r#"{"name": "Half", "datum": "Mid", "bodies"?: ["Body1"] (default: every body the plane divides)} — cuts bodies of the open design into cells by a datum plane, in memory (the design file is not changed); the model keeps the partition and applies it again whenever the design is opened, after the partitions before it. A cut body `B` becomes the cells `B/a` (on the plane's negative side) and `B/b` (several pieces on a side: `B/a1`, `B/a2`, …). The two faces of the cut are paired by name: `partition:<name>:a` on the cells on the negative side, `partition:<name>:b` on the positive side (`…#0`, `…#1` where a cell has several); every other face keeps the persistent name of the face it is a piece of (`<face>#k` for several pieces on one cell), so sets by face name still select it. Reports the cells made and the cut faces named; a plane that divides no body, or a listed body it does not divide, is an error"#,
+    params: r#"{"name": "Half", "datum": "Mid", "bodies"?: ["Body1"] (default: every body the plane divides; a body earlier partitions cut stands for its cells)} — cuts bodies of the open design into cells by a datum plane, in memory (the design file is not changed); the model keeps the partition and applies it again whenever the design is opened, after the partitions before it. A cut body `B` becomes the cells `B/a` (on the plane's negative side) and `B/b` (several pieces on a side: `B/a1`, `B/a2`, …). The two faces of the cut are paired by name: `partition:<name>:a` on the cells on the negative side, `partition:<name>:b` on the positive side (`…#0`, `…#1` where a cell has several); every other face keeps the persistent name of the face it is a piece of (`<face>#k` for several pieces on one cell), so sets by face name still select it. Reports the cells made and the cut faces named, and `warnings` when the plane lies on a face of a body it cuts or a cell's boundary does not tessellate into one a mesher takes (a cut through existing edges or vertices, such as a hole's axis), naming the plane, the cell and where; a body it cuts loses its mesh (`replaced`, as a mesher reports it; remesh the cells); a plane that divides no body, a listed body it does not divide, or a body the kernel fails to cut (its message) is an error"#,
    form: Some(super::forms::PARTITION),
    kind: CommandKind::Model,
    requires: &[Requirement::Design, Requirement::DatumPlane],
    run: partition,
 };

+pub const DATUM_SUPPRESS: CommandSpec = CommandSpec {
+    id: "geometry.datum.suppress",
+    label: "Suppress Datum",
+    params: r#"{"name": "Mid", "suppressed"?: true} — keeps the datum but leaves it out of the model (false brings it back): it cannot be an input to another datum, a partition, a mirror or a symmetry while suppressed, and the partitions that cut by it stop cutting (the design is cut again without them)"#,
+    form: Some(super::forms::DATUM_SUPPRESS),
+    kind: CommandKind::Model,
+    requires: &[Requirement::Datum],
+    run: datum_suppress,
+};
+
+pub const PARTITION_SUPPRESS: CommandSpec = CommandSpec {
+    id: "geometry.partition.suppress",
+    label: "Suppress Partition",
+    params: r#"{"name": "Half", "suppressed"?: true} — keeps the partition but leaves it out (false brings it back): the design is cut again without it, so its cells merge back into the bodies they came from and lose their meshes (`replaced`)"#,
+    form: Some(super::forms::PARTITION_SUPPRESS),
+    kind: CommandKind::Model,
+    requires: &[Requirement::Partition],
+    run: partition_suppress,
+};
+
 pub const PARTITION_DELETE: CommandSpec = CommandSpec {
    id: "geometry.partition.delete",
    label: "Delete Partition",
-    params: r#"{"name": "Half"} — removes a partition; the design is cut again by the ones left"#,
+    params: r#"{"name": "Half"} — removes a partition; the design is cut again by the ones left, and the cells that are gone lose their meshes (`replaced`)"#,
    form: Some(super::forms::PARTITION_DELETE),
    kind: CommandKind::Model,
    requires: &[Requirement::Partition],
@@ -214,18 +234,20 @@ fn sub(a: [f64; 3], b: [f64; 3]) -> [f64; 3] {

 /// The coordinates of datum point `name`.
 fn datum_point_at(m: &Model, name: &str) -> Result<[f64; 3]> {
-    match m.datum(name) {
-        Some(d) => d.point().ok_or_else(|| EngineError::Params(format!("datum `{name}` is a datum {}, not a point", d.kind()))),
-        None => Err(EngineError::Params(format!("no datum point `{name}`"))),
-    }
+    let d = m.usable_datum(name)?;
+    d.point().ok_or_else(|| EngineError::Params(format!("datum `{name}` is a datum {}, not a point", d.kind())))
 }

 /// The point and unit direction of datum axis `name`.
 fn datum_axis_of(m: &Model, name: &str) -> Result<([f64; 3], [f64; 3])> {
-    match m.datum(name) {
-        Some(d) => d.axis().ok_or_else(|| EngineError::Params(format!("datum `{name}` is a datum {}, not an axis", d.kind()))),
-        None => Err(EngineError::Params(format!("no datum axis `{name}`"))),
-    }
+    let d = m.usable_datum(name)?;
+    d.axis().ok_or_else(|| EngineError::Params(format!("datum `{name}` is a datum {}, not an axis", d.kind())))
+}
+
+/// The point and unit normal of datum plane `name`.
+pub(crate) fn datum_plane_of(m: &Model, name: &str) -> Result<([f64; 3], [f64; 3])> {
+    let d = m.usable_datum(name)?;
+    d.plane().ok_or_else(|| EngineError::Params(format!("datum `{name}` is a datum {}, not a plane", d.kind())))
 }

 /// A plane through three points; collinear points are refused relative to their spread.
@@ -296,14 +318,28 @@ fn point_datum(s: &Session, by: PointBy) -> Result<Datum> {
    let point = match by {
        PointBy::Coordinates { point } => point,
        PointBy::Vertex { body, vertex } => {
-            let m = &s.model;
-            let at = fieldcraft_model::GeometryRef::new(body.clone(), fieldcraft_model::Entity::Vertex(vertex.clone()))?;
-            let tags = m.classification().tags_selected_by(&at);
-            let node =
-                m.classification().nodes().iter().take(MAX_VERTEX_NODES).find(|(_, t)| tags.contains(t)).and_then(|(n, _)| m.node(*n)).ok_or_else(
-                    || EngineError::Params(format!("vertex `{vertex}` of body `{body}` is on no mesh node (vertices are named on meshed bodies)")),
-                )?;
-            node.xyz
+            // A vertex of the open design by its persistent name, else one the mesh tags.
+            let design_vertex = match s.design.as_deref().and_then(|d| d.body(&body)) {
+                Some(shape) => shape.vertices()?.into_iter().find(|v| v.name == vertex).map(|v| v.point),
+                None => None,
+            };
+            match design_vertex {
+                Some(point) => point,
+                None => {
+                    let m = &s.model;
+                    let at = fieldcraft_model::GeometryRef::new(body.clone(), fieldcraft_model::Entity::Vertex(vertex.clone()))?;
+                    let tags = m.classification().tags_selected_by(&at);
+                    let node = m
+                        .classification()
+                        .nodes()
+                        .iter()
+                        .take(MAX_VERTEX_NODES)
+                        .find(|(_, t)| tags.contains(t))
+                        .and_then(|(n, _)| m.node(*n))
+                        .ok_or_else(|| EngineError::Params(format!("body `{body}` has no vertex `{vertex}` (geometry.bodies lists its vertices)")))?;
+                    node.xyz
+                }
+            }
        }
        PointBy::Edge { body, edge, fraction } => {
            if !(0.0..=1.0).contains(&fraction) {
@@ -316,10 +352,7 @@ fn point_datum(s: &Session, by: PointBy) -> Result<Datum> {
        PointBy::FaceCentre { body, face } => shape(&body)?.face_centre(&face)?,
        PointBy::AxisPlane { axis, plane } => {
            let (p, d) = datum_axis_of(&s.model, &axis)?;
-            let (q, n) = match s.model.datum(&plane) {
-                Some(x) => x.plane().ok_or_else(|| EngineError::Params(format!("datum `{plane}` is a datum {}, not a plane", x.kind())))?,
-                None => return Err(EngineError::Params(format!("no datum plane `{plane}`"))),
-            };
+            let (q, n) = datum_plane_of(&s.model, &plane)?;
            let along = |a: [f64; 3], b: [f64; 3]| a[0] * b[0] + a[1] * b[1] + a[2] * b[2];
            let across = along(d, n);
            // Unit vectors: the sine of the angle between the axis and the plane.
@@ -342,6 +375,18 @@ fn datum_of(s: &Session, kind: &str, p: &Value) -> Result<Datum> {
    }
 }

+/// The datum a datum form's `params` define so far, for drawing it before OK; `None` when
+/// `command` makes no datum or the parameters do not define one yet. The model is not changed.
+pub fn preview(s: &Session, command: &str, params: &Value) -> Option<Datum> {
+    let kind = match command {
+        "geometry.datum" | "geometry.datum.edit" => "plane",
+        "geometry.datum.axis" | "geometry.datum.axis.edit" => "axis",
+        "geometry.datum.point" | "geometry.datum.point.edit" => "point",
+        _ => return None,
+    };
+    datum_of(s, kind, params).ok()
+}
+
 /// The parameters of the command that edits datum `name`, describing it as it is (a plane by
 /// its point and normal, an axis by its point and direction, a point by its coordinates); and
 /// that command.
@@ -392,10 +437,9 @@ fn datum_edit(s: &mut Session, p: &Value, kind: &str) -> Result<Value> {
    }
    let datum = datum_of(s, kind, p)?;
    s.model.replace_datum(name, datum)?;
-    if !s.model.datum_users(name).is_empty() {
-        recut(s)?;
-    }
-    Ok(datum_json(name, s.model.datum(name).unwrap_or(&datum)))
+    let cleared = if s.model.datum_users(name).is_empty() { super::replace::Cleared::default() } else { recut(s)? };
+    let reply = datum_json(name, s.model.datum(name).unwrap_or(&datum));
+    Ok(cleared.report_if_any(s, reply))
 }

 fn datum_delete(s: &mut Session, p: &Value) -> Result<Value> {
@@ -408,10 +452,9 @@ fn datum_delete(s: &mut Session, p: &Value) -> Result<Value> {
        }
    }
    s.model.remove_datum(name)?;
-    if cascade && !partitions.is_empty() {
-        recut(s)?;
-    }
-    Ok(json!({"deleted": name, "partitions": if cascade { partitions } else { Vec::new() }}))
+    let cleared = if cascade && !partitions.is_empty() { recut(s)? } else { super::replace::Cleared::default() };
+    let reply = json!({"deleted": name, "partitions": if cascade { partitions } else { Vec::new() }});
+    Ok(cleared.report_if_any(s, reply))
 }

 /// The model's partitions as cuts of the geometry.
@@ -419,6 +462,7 @@ fn cuts(model: &Model) -> Vec<Cut> {
    model
        .partitions()
        .iter()
+        .filter(|p| model.partition_cuts(p))
        .filter_map(|p| {
            let (point, normal) = model.datum(&p.datum)?.plane()?;
            Some(Cut { name: p.name.clone(), point, normal, bodies: p.bodies.clone() })
@@ -426,26 +470,44 @@ fn cuts(model: &Model) -> Vec<Cut> {
        .collect()
 }

-/// `design` cut by `model`'s partitions (the design as opened when the model has none).
+/// `design` cut by `model`'s partitions, then with its face merges and its face splits (those
+/// along a suppressed datum left out; the design as opened when the model has none).
 pub(crate) fn partitioned(design: &Design, model: &Model) -> Result<Design> {
-    Ok(design.partitioned(&cuts(model))?)
+    let merges: Vec<Merge> = model
+        .face_merges()
+        .iter()
+        .map(|m| Merge { name: m.name.clone(), body: m.body.clone(), faces: m.faces.clone(), into: m.into.clone() })
+        .collect();
+    let splits: Vec<fieldcraft_geometry::face_split::FaceSplit> = model
+        .face_splits()
+        .iter()
+        .filter(|s| !model.datum_suppressed(&s.datum))
+        .filter_map(|s| {
+            let (point, normal) = model.datum(&s.datum)?.plane()?;
+            Some(fieldcraft_geometry::face_split::FaceSplit { name: s.name.clone(), body: s.body.clone(), face: s.face.clone(), point, normal })
+        })
+        .collect();
+    Ok(design.partitioned(&cuts(model))?.merged(&merges)?.split(&splits)?)
 }

-/// Cut the session's design by its model's partitions again.
-fn recut(s: &mut Session) -> Result<()> {
-    if let Some(d) = &s.design {
-        let cut = partitioned(d, &s.model)?;
-        s.design = Some(Arc::new(cut));
-    }
-    Ok(())
+/// Cut the session's design by its model's partitions again (and merge its faces again). The bodies that are gone (cells
+/// whose partition went, a body a new partition cut) take their meshes with them (#385): what
+/// went is in the returned [`super::replace::Cleared`], which the command reports.
+pub(super) fn recut(s: &mut Session) -> Result<super::replace::Cleared> {
+    let Some(d) = &s.design else { return Ok(super::replace::Cleared::default()) };
+    let cut = partitioned(d, &s.model)?;
+    let gone: Vec<String> = d.bodies.iter().filter(|b| cut.body(&b.name).is_none()).map(|b| b.name.clone()).collect();
+    s.design = Some(Arc::new(cut));
+    Ok(super::replace::clear(&mut s.model, gone.iter().map(String::as_str)))
 }

 fn partition(s: &mut Session, p: &Value) -> Result<Value> {
    let name = super::name(p)?.to_string();
    let datum: String = super::req(p, "datum")?;
    let bodies: Vec<String> = super::opt(p, "bodies")?.unwrap_or_default();
-    s.model.add_partition(Partition { name: name.clone(), datum: datum.clone(), bodies })?;
-    recut(s)?;
+    datum_plane_of(&s.model, &datum)?;
+    s.model.add_partition(Partition { name: name.clone(), datum: datum.clone(), bodies, suppressed: false })?;
+    let cleared = recut(s)?;
    let design = s.design.as_deref().ok_or_else(|| EngineError::Params("open a design first".into()))?;
    let feature = format!("partition {name}");
    let errors: Vec<&str> = design.errors.iter().filter(|e| e.feature == feature).map(|e| e.message.as_str()).collect();
@@ -459,26 +521,68 @@ fn partition(s: &mut Session, p: &Value) -> Result<Value> {
    }
    let cells: Vec<String> = design.bodies.iter().map(|b| b.name.clone()).filter(|b| split.iter().any(|x| b.starts_with(&format!("{x}/")))).collect();
    let (faces, bodies): (usize, Vec<String>) = (report.map_or(0, |r| r.faces), design.bodies.iter().map(|b| b.name.clone()).collect());
+    let mut warnings: Vec<String> = report.map(|r| r.warnings.clone()).unwrap_or_default();
+    for cell in &cells {
+        if let Some(why) = design.body(cell).and_then(|shape| unmeshable(shape, None).err()) {
+            warnings.push(format!(
+                "partition `{name}`: cell `{cell}` has a boundary no mesher takes ({why}): the plane passes within the kernel's tolerance of a face, edge or vertex it cut (along a face, through the axis of a hole); move the plane off it (by a fraction of the element size)"
+            ));
+        }
+    }
    // The cut shows as edges on the cells, so the plane steps out of the way (view state, #295):
    // selecting it in the browser or its eye shows it again.
    if s.view.hidden.len() < MAX_HIDDEN {
        s.view.hidden.insert(Item { kind: ItemKind::Datum, name: datum });
    }
-    Ok(json!({
+    let mut reply = json!({
        "name": name,
        "split": split,
        "cells": cells,
        "cut_faces": faces,
        "bodies": bodies,
-    }))
+    });
+    if !warnings.is_empty()
+        && let Some(o) = reply.as_object_mut()
+    {
+        o.insert("warnings".into(), json!(warnings));
+    }
+    Ok(cleared.report_if_any(s, reply))
+}
+
+/// Whether a cell's boundary, tessellated as the meshers take it (by default, or at `tolerance`), bounds a volume mesh:
+/// the defects (open edges, edges on three triangles) when it does not.
+pub(super) fn unmeshable(shape: &fieldcraft_geometry::Shape, tolerance: Option<f64>) -> Result<()> {
+    let input = super::hex::shape_input(shape, tolerance)?;
+    let options = fieldcraft_mesh::surface::SurfaceOptions { weld_distance: input.mesh.weld_distance, ..Default::default() };
+    fieldcraft_mesh::surface::BoundarySurface::new(&input.mesh.positions, &input.mesh.triangles, &input.mesh.tri_face, &options)
+        .map(|_| ())
+        .map_err(|e| EngineError::Params(e.to_string()))
+}
+
+fn datum_suppress(s: &mut Session, p: &Value) -> Result<Value> {
+    let name = super::name(p)?;
+    let suppressed = super::opt(p, "suppressed")?.unwrap_or(true);
+    s.model.set_datum_suppressed(name, suppressed)?;
+    let cleared = recut(s)?;
+    let bodies: Vec<String> = s.design.iter().flat_map(|d| d.bodies.iter().map(|b| b.name.clone())).collect();
+    Ok(cleared.report_if_any(s, json!({"name": name, "suppressed": suppressed, "bodies": bodies})))
+}
+
+fn partition_suppress(s: &mut Session, p: &Value) -> Result<Value> {
+    let name = super::name(p)?;
+    let suppressed = super::opt(p, "suppressed")?.unwrap_or(true);
+    s.model.set_partition_suppressed(name, suppressed)?;
+    let cleared = recut(s)?;
+    let bodies: Vec<String> = s.design.iter().flat_map(|d| d.bodies.iter().map(|b| b.name.clone())).collect();
+    Ok(cleared.report_if_any(s, json!({"name": name, "suppressed": suppressed, "bodies": bodies})))
 }

 fn partition_delete(s: &mut Session, p: &Value) -> Result<Value> {
    let name = super::name(p)?;
    s.model.remove_partition(name)?;
-    recut(s)?;
+    let cleared = recut(s)?;
    let bodies: Vec<String> = s.design.iter().flat_map(|d| d.bodies.iter().map(|b| b.name.clone())).collect();
-    Ok(json!({"deleted": name, "bodies": bodies}))
+    Ok(cleared.report_if_any(s, json!({"deleted": name, "bodies": bodies})))
 }

 #[cfg(test)]
@@ -549,6 +653,31 @@ pub(crate) mod tests {
        assert!(s.journal.is_empty());
    }

+    /// Suppressing a partition merges its cells back; suppressing its datum does too and stops
+    /// the datum being an input; unsuppressing cuts again; each is one undo step (#291).
+    #[test]
+    fn suppressed_partitions_and_datums_leave_the_design_uncut() {
+        let (mut s, dir) = plate();
+        s.execute("geometry.datum", &json!({"name": "Mid", "by": {"type": "offset", "plane": "yz", "offset": 15}})).unwrap();
+        s.execute("geometry.partition", &json!({"name": "Half", "datum": "Mid"})).unwrap();
+        let count = |s: &Session| s.design.as_ref().map_or(0, |d| d.bodies.len());
+        assert_eq!(count(&s), 2);
+        let r = s.execute("geometry.partition.suppress", &json!({"name": "Half"})).unwrap();
+        assert_eq!((r["suppressed"].as_bool(), count(&s)), (Some(true), 1));
+        s.execute("geometry.partition.suppress", &json!({"name": "Half", "suppressed": false})).unwrap();
+        assert_eq!(count(&s), 2);
+        s.execute("geometry.datum.suppress", &json!({"name": "Mid"})).unwrap();
+        assert_eq!(count(&s), 1);
+        let e = s.execute("geometry.partition", &json!({"name": "Again", "datum": "Mid"})).unwrap_err().to_string();
+        assert!(e.contains("suppressed"), "{e}");
+        let e = s.execute("geometry.datum.point", &json!({"name": "P", "by": {"type": "axis_plane", "axis": "Mid", "plane": "Mid"}}));
+        assert!(e.is_err());
+        s.execute("edit.undo", &json!({})).unwrap();
+        assert_eq!(count(&s), 2, "undo cuts again");
+        assert!(s.execute("geometry.datum.suppress", &json!({"name": "Nope"})).is_err());
+        let _ = std::fs::remove_dir_all(dir);
+    }
+
    #[test]
    fn a_partition_cuts_the_design_and_is_replayed_when_it_opens_again() {
        let (mut s, dir) = plate();
@@ -727,4 +856,146 @@ pub(crate) mod tests {
        assert_eq!(s.journal.len(), journal);
        let _ = std::fs::remove_dir_all(&dir);
    }
+
+    /// A session with the design `commands` (a SolidCraft script) open.
+    pub(crate) fn scripted(commands: Value) -> (crate::tests::TempDir, Session) {
+        let bytes = fieldcraft_geometry::script_design(&json!({"commands": commands}).to_string()).unwrap();
+        let (dir, path) = crate::tests::design_file(&bytes);
+        let mut s = Session::default();
+        s.execute("geometry.open", &json!({"path": path})).unwrap();
+        (dir, s)
+    }
+
+    /// Partition the open design by the planes `x = …` / `y = …` / `z = …` (`(axis, offset)`).
+    pub(crate) fn cut_at(s: &mut Session, planes: &[(usize, f64)]) {
+        for (i, &(k, offset)) in planes.iter().enumerate() {
+            let (name, plane) = (format!("C{i}"), ["yz", "zx", "xy"][k]);
+            s.execute("geometry.datum", &json!({"name": name, "by": {"type": "offset", "plane": plane, "offset": offset}})).unwrap();
+            s.execute("geometry.partition", &json!({"name": format!("P{i}"), "datum": name})).unwrap();
+        }
+    }
+
+    /// A box with a plate-shaped void in its middle that touches no side (#388): the planes
+    /// round the void leave a centre column whose material lies above and below the void, two
+    /// pieces that become separate cells only at the last cut.
+    #[test]
+    fn pieces_that_do_not_touch_are_separate_cells() {
+        let (_dir, mut s) = scripted(json!([
+            {"command": "solid.box", "params": {"length": 106, "width": 76, "height": 20, "corner": [0, 0, 0], "body_name": "Air"}},
+            {"command": "solid.box", "params": {"length": 85, "width": 56, "height": 2, "corner": [13, 13, 9], "operation": "cut"}},
+        ]));
+        let whole = s.design.as_ref().unwrap().bodies[0].measure().unwrap().volume;
+        cut_at(&mut s, &[(0, 22.5), (0, 68.5), (1, 22.5), (1, 59.5)]);
+        let design = s.design.clone().unwrap();
+        let shells: Vec<(&str, usize)> = design.bodies.iter().map(|b| (b.name.as_str(), b.shells().unwrap())).collect();
+        assert!(shells.iter().all(|s| s.1 == 1), "{shells:?}");
+        // 3 × 3 columns, the centre one in two pieces.
+        assert_eq!(shells.len(), 10, "{shells:?}");
+        let volume: f64 = design.bodies.iter().map(|b| b.measure().unwrap().volume).sum();
+        assert!((volume - whole).abs() < 1e-6 * whole, "{volume} vs {whole}");
+        let centre: Vec<&str> = shells.iter().map(|s| s.0).filter(|n| n.ends_with('1') || n.ends_with('2')).collect();
+        assert_eq!(centre.len(), 2, "{centre:?}");
+        // Numbered by centroid: the piece below the void first.
+        let z = |n: &str| design.body(n).unwrap().measure().unwrap().centroid[2];
+        assert!(z(centre[0]) < 9.0 && z(centre[1]) > 11.0, "{centre:?}");
+    }
+
+    /// #385: the cells' meshes go with the cells (deleting, suppressing or replacing their
+    /// partitions), a body's mesh goes when a partition cuts it, and meshes left over from an
+    /// earlier cut are listed by model.check and removed by mesh.clear.
+    #[test]
+    fn meshes_go_with_the_bodies_partitions_remove() {
+        let (mut s, dir) = plate();
+        let whole = s.design.as_ref().unwrap().bodies[0].measure().unwrap().volume;
+        let volume = |s: &mut Session| s.execute("mesh.quality", &json!({})).unwrap()["volume"].as_f64().unwrap();
+        // Partitioning a meshed body takes its mesh.
+        s.execute("mesh.hex.generate", &json!({"size": 2.5})).unwrap();
+        s.execute("geometry.datum", &json!({"name": "X30", "by": {"type": "offset", "plane": "yz", "offset": 30}})).unwrap();
+        let r = s.execute("geometry.partition", &json!({"name": "P", "datum": "X30"})).unwrap();
+        assert_eq!(r["replaced"][0]["body"], "Body1", "{r}");
+        assert!(s.model.elements().is_empty());
+        // Deleting the datum with its partition takes the cells' meshes; the whole body's new
+        // mesh is the only one.
+        s.execute("mesh.cells", &json!({"default": "hex", "size": 2.5})).unwrap();
+        let r = s.execute("geometry.datum.delete", &json!({"name": "X30", "cascade": true})).unwrap();
+        let gone: Vec<&str> = r["replaced"].as_array().unwrap().iter().map(|b| b["body"].as_str().unwrap()).collect();
+        assert_eq!(gone, ["Body1/a", "Body1/b"], "{r}");
+        assert!(s.model.elements().is_empty());
+        s.execute("mesh.hex.generate", &json!({"size": 2.5})).unwrap();
+        let v = volume(&mut s);
+        assert!((v - whole).abs() < 1e-2 * whole, "{v} vs {whole}");
+        // Suppressing or deleting a partition does the same.
+        s.execute("geometry.datum", &json!({"name": "X30", "by": {"type": "offset", "plane": "yz", "offset": 30}})).unwrap();
+        s.execute("geometry.partition", &json!({"name": "P", "datum": "X30"})).unwrap();
+        s.execute("mesh.cells", &json!({"default": "hex", "size": 2.5})).unwrap();
+        let r = s.execute("geometry.partition.suppress", &json!({"name": "P"})).unwrap();
+        assert_eq!(r["replaced"].as_array().map(Vec::len), Some(2), "{r}");
+        s.execute("edit.undo", &json!({})).unwrap();
+        assert!(!s.model.elements().is_empty(), "undo brings the cells' meshes back");
+        let r = s.execute("geometry.partition.delete", &json!({"name": "P"})).unwrap();
+        assert_eq!(r["replaced"].as_array().map(Vec::len), Some(2), "{r}");
+        // A mesh left from an earlier cut (a model saved before the cut changed): listed and
+        // cleared.
+        s.execute("geometry.partition", &json!({"name": "P", "datum": "X30"})).unwrap();
+        s.execute("mesh.cells", &json!({"default": "hex", "size": 2.5})).unwrap();
+        s.model.remove_partition("P").unwrap();
+        let d = s.design.clone().unwrap();
+        s.design = Some(Arc::new(partitioned(&d, &s.model).unwrap()));
+        let check = s.execute("model.check", &json!({})).unwrap();
+        let listed: Vec<&str> =
+            check["diagnostics"].as_array().unwrap().iter().filter_map(|d| d["subject"].as_str()).filter(|d| d.starts_with("body")).collect();
+        assert_eq!(listed, ["body `Body1/a`", "body `Body1/b`"], "{check}");
+        let r = s.execute("mesh.clear", &json!({})).unwrap();
+        assert_eq!(r["replaced"].as_array().map(Vec::len), Some(2), "{r}");
+        assert!(s.model.elements().is_empty());
+        assert!(s.execute("mesh.clear", &json!({"bodies": ["Body1"]})).is_err(), "nothing to clear");
+        let _ = std::fs::remove_dir_all(&dir);
+    }
+
+    /// The Raspberry Pi 5 enclosure analysis design (base, lid, heat sink, board, chips and the
+    /// air inside), its SolidCraft recipe.
+    pub(crate) fn pi5() -> (crate::tests::TempDir, Session) {
+        scripted(serde_json::from_str(include_str!("../../tests/designs/pi5-enclosure.json")).unwrap())
+    }
+
+    /// #384: cuts stay on their plane (the kernel's own split put them 1.8 µm off it on the air
+    /// of the enclosure, so the cut faces were not even recognized), and a plane along an
+    /// existing face or through a hole's axis is a warning naming the plane, the body and where,
+    /// or refused where the kernel could only cut it off the plane.
+    #[test]
+    fn cuts_stay_on_the_plane_and_risky_ones_are_named() {
+        let (_dir, mut s) = pi5();
+        let plane = |s: &mut Session, name: &str, x: f64| {
+            s.execute("geometry.datum", &json!({"name": name, "by": {"type": "offset", "plane": "yz", "offset": x}})).unwrap();
+            s.execute("geometry.partition", &json!({"name": format!("P{name}"), "datum": name, "bodies": ["Air"]})).unwrap()
+        };
+        // Beside the board's mounting holes: clean cells, cut faces on the plane.
+        let r = plane(&mut s, "X", 16.5);
+        assert!(r.get("warnings").is_none(), "{r}");
+        let design = s.design.clone().unwrap();
+        for cell in ["Air/a", "Air/b"] {
+            let shape = design.body(cell).unwrap();
+            let cut: Vec<f64> = shape
+                .faces()
+                .iter()
+                .zip(shape.face_surfaces().unwrap())
+                .filter(|(f, _)| f.name.starts_with("partition:PX:"))
+                .filter_map(|(_, srf)| match srf {
+                    Some(fieldcraft_geometry::FaceSurface::Plane { point, .. }) => Some(point[0]),
+                    _ => None,
+                })
+                .collect();
+            assert!(!cut.is_empty() && cut.iter().all(|x| (x - 16.5).abs() < 1e-9), "{cell}: {cut:?}");
+        }
+        s.execute("edit.undo", &json!({})).unwrap();
+        // Along the side of the heat sink's pedestal: the kernel only cuts with its box nudged
+        // off the plane, so the cut is refused, saying why (#427).
+        s.execute("geometry.datum", &json!({"name": "Side", "by": {"type": "offset", "plane": "yz", "offset": 34.0}})).unwrap();
+        let e = s.execute("geometry.partition", &json!({"name": "PSide", "datum": "Side", "bodies": ["Air"]})).unwrap_err().to_string();
+        assert!(e.contains("could not cut `Air`") && e.contains("only made off the plane"), "{e}");
+        // Through a standoff's hole: the cell whose boundary breaks at the hole's edge is named.
+        let r = plane(&mut s, "Axis", 74.5);
+        let warnings = r["warnings"].to_string();
+        assert!(warnings.contains("partition `PAxis`: cell `Air/") && warnings.contains("boundary no mesher takes"), "{r}");
+    }
 }
@@ -13,6 +13,9 @@ use fieldcraft_model::{
 use serde::de::DeserializeOwned;
 use serde_json::{Value, json};

+use fieldcraft_io::{Item, ItemKind};
+use fieldcraft_model::rename::Kind as RenameKind;
+
 use super::{name, opt, req};
 use crate::requirement::Requirement;
 use crate::{CommandKind, CommandSpec, EngineError, Result, Session};
@@ -92,7 +95,7 @@ definition_commands!(
    Material,
    "material",
    "Material",
-    r#"{"name": "Steel", "elastic": {"type": "isotropic", "young": 210000, "poisson": 0.3} | {"type": "engineering_constants", "young": [E1, E2, E3], "poisson": [ν12, ν13, ν23], "shear": [G12, G13, G23]}, "density": 7.85e-9, "fluid": {"type": "newtonian", "viscosity": 1.0e-9} (dynamic viscosity; a fluid needs a density), "plastic": {…} (see model.material.plasticity), "damage": {…}, "erosion": {…} (see model.material.damage), "hyperelastic": {"type": "neo_hookean"} | {"type": "mooney_rivlin", "c01": 0.1} (C10 = μ/2 − C01) | {"type": "yeoh", "c20": -0.01, "c30": 0.001} (C10 = μ/2) (large strain in nonlinear steps, from the isotropic constants: μ = E/(2(1 + ν)), κ = E/(3(1 − 2ν)); without it an elastic material is St Venant–Kirchhoff there)} — in the model's unit system (model.units), never converted"#,
+    r#"{"name": "Steel", "elastic": {"type": "isotropic", "young": 210000, "poisson": 0.3} | {"type": "engineering_constants", "young": [E1, E2, E3], "poisson": [ν12, ν13, ν23], "shear": [G12, G13, G23]}, "density": 7.85e-9, "fluid": {"type": "newtonian", "viscosity": 1.0e-9} (dynamic viscosity; a fluid needs a density), "plastic": {…} (see model.material.plasticity), "damage": {…}, "erosion": {…} (see model.material.damage), "hyperelastic": {"type": "neo_hookean"} | {"type": "mooney_rivlin", "c01": 0.1} (C10 = μ/2 − C01) | {"type": "yeoh", "c20": -0.01, "c30": 0.001} (C10 = μ/2) (large strain in nonlinear steps, from the isotropic constants: μ = E/(2(1 + ν)), κ = E/(3(1 − 2ν)); without it an elastic material is St Venant–Kirchhoff there), "thermal": {"conductivity": 0.05 | [kx, ky, kz], "specific_heat": 4.6e8, "expansion": 1.2e-5 | [αx, αy, αz], "reference_temperature": 20 (zero thermal strain; default 0)} (heat transfer and thermal strain; each key optional)} — in the model's unit system (model.units), never converted"#,
    super::forms::MATERIAL,
    super::forms::MATERIAL_DELETE,
    add_material,
@@ -249,7 +252,7 @@ definition_commands!(
    BoundaryCondition,
    "boundary_condition",
    "Boundary Condition",
-    r#"{"name": "clamp", "type": "fixed", "target": {"set": "root"} | {"reference_point": "RP"}} | {"name", "type": "displacement", "target", "values": [u1, u2, u3, ur1, ur2, ur3] (null leaves a degree of freedom free)} | {"name", "type": "symmetry", "target", "plane": "x|y|z" (the plane's normal)} — active in the steps that list it (model.step.activate)"#,
+    r#"{"name": "clamp", "type": "fixed", "target": {"set": "root"} | {"reference_point": "RP"}} | {"name", "type": "displacement", "target", "values": [u1, u2, u3, ur1, ur2, ur3] (null leaves a degree of freedom free)} | {"name", "type": "symmetry", "target", "plane": "x|y|z" | {"normal": [nx, ny, nz]} (the plane's normal; an inclined plane holds n · u = 0 and the rotations about its in-plane axes)} — active in the steps that list it (model.step.activate)"#,
    super::forms::BOUNDARY_CONDITION,
    super::forms::BOUNDARY_CONDITION_DELETE,
    add_boundary_condition,
@@ -267,7 +270,7 @@ definition_commands!(
    Load,
    "load",
    "Load",
-    r#"{"name": "push", "type": "force|moment", "target": {"set": "…"} | {"reference_point": "…"}, "vector": [x, y, z], "distribution": "total" (default: the vector is the total, split by area over the set's faces, or equally over its nodes) | "per_node" (at every node: depends on the mesh)} | {"name", "type": "traction", "set", "vector" (per area, on the set's faces)} | {"name", "type": "pressure", "set", "magnitude" (positive pushes in)} | {"name", "type": "gravity", "acceleration": [x, y, z], "set" (optional, default the whole model)} | {"name", "type": "body_force", "set", "vector" (per volume)} | {"name", "type": "centrifugal", "angular_velocity" (rad per time unit), "point": [x, y, z] (on the axis), "axis": [x, y, z], "set" (optional)} — 2D models: in-plane vectors, surface loads on element edges; active in the steps that list it (model.step.activate)"#,
+    r#"{"name": "push", "type": "force|moment", "target": {"set": "…"} | {"reference_point": "…"}, "vector": [x, y, z], "distribution": "total" (default: the vector is the total, split by area over the set's faces, or equally over its nodes) | "per_node" (at every node: depends on the mesh)} | {"name", "type": "traction", "set", "vector" (per area, on the set's faces)} | {"name", "type": "pressure", "set", "magnitude" (positive pushes in)} | {"name", "type": "gravity", "acceleration": [x, y, z], "set" (optional, default the whole model)} | {"name", "type": "body_force", "set", "vector" (per volume)} | {"name", "type": "centrifugal", "angular_velocity" (rad per time unit), "point": [x, y, z] (on the axis), "axis": [x, y, z], "set" (optional)} | {"name", "type": "surface_flux", "set", "flux" (heat per area into the set's faces)} | {"name", "type": "convection", "set", "film" (film coefficient h), "sink" (surrounding temperature): heat flux h (sink − T) into the set's faces} | {"name", "type": "heat_source", "set", "power" (heat per volume in the set's elements)} | {"name", "type": "temperature", "target": {"set": "…"} | {"reference_point": "…"}, "value" (a temperature that strains the material in stress steps)} — heat loads act in heat transfer and coupled steps; 2D models: in-plane vectors, surface loads on element edges; active in the steps that list it (model.step.activate)"#,
    super::forms::LOAD,
    super::forms::LOAD_DELETE,
    add_load,
@@ -319,7 +322,7 @@ fn fluid_boundary(s: &mut Session, p: &Value) -> Result<Value> {
 pub const STEP_CREATE: CommandSpec = CommandSpec {
    id: "model.step.create",
    label: "New Step",
-    params: r#"{"name": "Bend", "procedure": {"type": "static"} | {"type": "nonlinear_static", "nonlinear_geometry": true, "initial_increment": 0.1, "min_increment": 1e-5, "max_increment": 1.0 (fractions of the step), "max_increments": 100, "max_iterations": 16 (per increment), "tolerances": {"force": 1e-6, "displacement": 1e-5, "energy": 1e-10}, "line_search": false, "load_path": [[0, 0], [0.5, 1], [1, 0]] (optional: the load factor against the step fraction, piecewise linear from [0, 0] to fraction 1; increments end at its points)} (loads and prescribed displacements are the load factor times their values; it ramps from 0 to 1 without a load path) | {"type": "frequency", "modes": 10, "min_hz": 0, "max_hz": 500} | {"type": "fluid", "domain": "Flow", "end_time": 1.0 | "steps": 1000, "time_step": (default: chosen for Mach 0.087 and τ ≤ 1), "frames": 10, "magic": 0.1875 (the two-relaxation-time Λ)} | {"type": "explicit_dynamic", "end_time": 0.001, "dt_scale": 0.9, "max_increments": 10000000, "output_interval", "history_interval", "history_nodes": "set", "initial_velocities": [{"set", "velocity": [vx, vy, vz]}], "rigid_walls": [{"set", "point", "normal", "friction": {"static": 0.3, "kinetic": 0.2, "decay": 10} (Coulomb; default frictionless)}], "hourglass": {"type": "viscous|stiffness", "coefficient": 0.1}, "bulk_viscosity": {"linear": 0.06, "quadratic": 1.5}, "mass_scaling": {"target_increment": 1e-6, "set": "…" (optional, default every element)} (opt-in: elements below the target increment get the density that reaches it; the added mass is reported)}, "output": ["displacement", "reaction_force", "stress", "strain"] (default by procedure), "boundary_conditions": [names], "loads": [names] (active in this step; nothing carries over between steps), "before": "step" (default: last)}"#,
+    params: r#"{"name": "Bend", "procedure": {"type": "static"} | {"type": "nonlinear_static", "nonlinear_geometry": true, "initial_increment": 0.1, "min_increment": 1e-5, "max_increment": 1.0 (fractions of the step), "max_increments": 100, "max_iterations": 16 (per increment), "tolerances": {"force": 1e-6, "displacement": 1e-5, "energy": 1e-10}, "line_search": false, "load_path": [[0, 0], [0.5, 1], [1, 0]] (optional: the load factor against the step fraction, piecewise linear from [0, 0] to fraction 1; increments end at its points)} (loads and prescribed displacements are the load factor times their values; it ramps from 0 to 1 without a load path) | {"type": "frequency", "modes": 10, "min_hz": 0, "max_hz": 500} | {"type": "buckle", "modes": 5, "shift"?: 0} | {"type": "heat_transfer", "transient"?: {"end_time": 10, "increment": 0.5, "theta": 1, "initial_temperature": 20}} (steady without `transient`) | {"type": "coupled_temperature_displacement"} (steady heat and the static equilibrium of its thermal strains) | {"type": "fluid", "domain": "Flow", "end_time": 1.0 | "steps": 1000, "time_step": (default: chosen for Mach 0.087 and τ ≤ 1), "frames": 10, "magic": 0.1875 (the two-relaxation-time Λ)} | {"type": "explicit_dynamic", "end_time": 0.001, "dt_scale": 0.9, "max_increments": 10000000, "output_interval", "history_interval", "history_nodes": "set", "initial_velocities": [{"set", "velocity": [vx, vy, vz]}], "rigid_walls": [{"set", "point", "normal", "friction": {"static": 0.3, "kinetic": 0.2, "decay": 10} (Coulomb; default frictionless)}], "hourglass": {"type": "viscous|stiffness", "coefficient": 0.1}, "bulk_viscosity": {"linear": 0.06, "quadratic": 1.5}, "mass_scaling": {"target_increment": 1e-6, "set": "…" (optional, default every element)} (opt-in: elements below the target increment get the density that reaches it; the added mass is reported)}, "output": ["displacement", "reaction_force", "stress", "strain"] (default by procedure), "boundary_conditions": [names], "loads": [names] (active in this step; nothing carries over between steps), "before": "step" (default: last)}"#,
    form: Some(super::forms::STEP_CREATE),
    kind: CommandKind::Model,
    requires: &[],
@@ -356,6 +359,60 @@ pub const STEP_ACTIVATE: CommandSpec = CommandSpec {
    run: step_activate,
 };

+pub const RENAME: CommandSpec = CommandSpec {
+    id: "model.rename",
+    label: "Rename",
+    params: r#"{"kind": "set" | "material" | "section" | "step" | "boundary_condition" | "load" | "reference_point" | "coupling" | "contact" | "tie" | "point_mass" | "spring" | "fluid_domain" | "datum", "from": "end", "to": "Tip"} — renames the definition and every reference to it (sets in sections, couplings, contacts, ties, discrete elements, boundary conditions, loads and explicit steps; materials in sections and fluid domains; reference points; boundary conditions and loads in the steps they are active in; steps in imperfections; fluid domains in fluid steps; datum planes in partitions). A name already taken is refused; the viewport's hidden items follow the new name"#,
+    form: Some(super::forms::RENAME),
+    kind: CommandKind::Model,
+    requires: &[],
+    run: rename,
+};
+
+/// `model.rename`'s kinds, as the command takes them.
+pub const RENAME_KINDS: &[(&str, RenameKind)] = &[
+    ("set", RenameKind::Set),
+    ("material", RenameKind::Material),
+    ("section", RenameKind::Section),
+    ("step", RenameKind::Step),
+    ("boundary_condition", RenameKind::BoundaryCondition),
+    ("load", RenameKind::Load),
+    ("reference_point", RenameKind::ReferencePoint),
+    ("coupling", RenameKind::Coupling),
+    ("contact", RenameKind::Contact),
+    ("tie", RenameKind::Tie),
+    ("point_mass", RenameKind::PointMass),
+    ("spring", RenameKind::Spring),
+    ("fluid_domain", RenameKind::FluidDomain),
+    ("datum", RenameKind::Datum),
+];
+
+fn rename(s: &mut Session, p: &Value) -> Result<Value> {
+    let kind: &str = req(p, "kind")?;
+    let from: &str = req(p, "from")?;
+    let to: &str = req(p, "to")?;
+    let Some((_, k)) = RENAME_KINDS.iter().find(|(id, _)| *id == kind) else {
+        let kinds: Vec<&str> = RENAME_KINDS.iter().map(|(id, _)| *id).collect();
+        return Err(EngineError::Params(format!("`kind` is one of {}", kinds.join(", "))));
+    };
+    s.model.rename(*k, from, to)?;
+    // What the viewport hides follows the new name.
+    let item = match k {
+        RenameKind::Datum => Some(ItemKind::Datum),
+        RenameKind::BoundaryCondition => Some(ItemKind::BoundaryCondition),
+        RenameKind::Load => Some(ItemKind::Load),
+        RenameKind::ReferencePoint => Some(ItemKind::ReferencePoint),
+        RenameKind::Coupling => Some(ItemKind::Coupling),
+        _ => None,
+    };
+    if let Some(kind) = item
+        && s.view.hidden.remove(&Item { kind, name: from.to_string() })
+    {
+        s.view.hidden.insert(Item { kind, name: to.to_string() });
+    }
+    Ok(json!({"kind": kind, "from": from, "name": to}))
+}
+
 pub const ACTIVITY: CommandSpec = CommandSpec {
    id: "model.activity",
    label: "Step Table",
@@ -473,6 +530,27 @@ pub(crate) mod tests {
        s.run_script(&script).unwrap();
    }

+    /// A rename rewrites the references, checks clean, is undone in one step, follows the hidden
+    /// state and refuses a name in use (#290).
+    #[test]
+    fn rename_keeps_the_model_whole_and_undoes() {
+        let mut s = Session::default();
+        defined_bar(&mut s);
+        s.execute("view.hide", &json!({"items": [{"kind": "load", "name": "push"}]})).unwrap();
+        s.execute("model.rename", &json!({"kind": "set", "from": "end", "to": "Tip"})).unwrap();
+        s.execute("model.rename", &json!({"kind": "load", "from": "push", "to": "Push"})).unwrap();
+        s.execute("model.rename", &json!({"kind": "step", "from": "Bend", "to": "Load"})).unwrap();
+        assert!(s.model.sets().get("end").is_none() && !s.model.set_users("Tip").is_empty());
+        assert!(s.model.step("Load").is_some_and(|st| st.loads.contains("Push")));
+        assert!(s.view.is_hidden(fieldcraft_io::ItemKind::Load, "Push") && !s.view.is_hidden(fieldcraft_io::ItemKind::Load, "push"));
+        assert_eq!(s.execute("model.check", &json!({})).unwrap()["ready"], true);
+        let e = s.execute("model.rename", &json!({"kind": "set", "from": "Tip", "to": "root"})).unwrap_err().to_string();
+        assert!(e.contains("already exists"), "{e}");
+        assert!(s.execute("model.rename", &json!({"kind": "partition", "from": "a", "to": "b"})).is_err());
+        s.execute("edit.undo", &json!({})).unwrap();
+        assert!(s.model.step("Bend").is_some() && s.model.step("Load").is_none());
+    }
+
    #[test]
    fn a_script_defines_a_model_that_checks_clean() {
        let mut s = Session::default();
@@ -30,6 +30,16 @@ pub const CRASH_REPORT: CommandSpec = CommandSpec {
    run: crash_report,
 };

+pub const CRASH_REPORTS_DELETE: CommandSpec = CommandSpec {
+    id: "diagnostics.crash_reports.delete",
+    label: "Delete Crash Reports",
+    params: r#"{"id": "20261014-101500-…"} or {"all": true}; "dir"?: "…" — deletes one crash report, or all of them, from this computer: how many were deleted"#,
+    form: Some(super::forms::CRASH_REPORTS_DELETE),
+    kind: CommandKind::Session,
+    requires: &[],
+    run: crash_reports_delete,
+};
+
 pub const BUG_REPORT: CommandSpec = CommandSpec {
    id: "diagnostics.bug_report",
    label: "Report a Bug",
@@ -51,8 +61,12 @@ pub const CRASH_TEST: CommandSpec = CommandSpec {
 };

 fn crash_dir(s: &Session, p: &Value) -> Result<PathBuf> {
+    crash_dir_for(s, p, Access::Read)
+}
+
+fn crash_dir_for(s: &Session, p: &Value, access: Access) -> Result<PathBuf> {
    if p.get("dir").is_some() {
-        return Ok(PathBuf::from(file_param(s, p, "dir", Access::Read)?));
+        return Ok(PathBuf::from(file_param(s, p, "dir", access)?));
    }
    crash::default_dir().ok_or_else(|| EngineError::Params("no crash folder: set FIELDCRAFT_CRASH_DIR or give `dir`".into()))
 }
@@ -71,6 +85,21 @@ fn crash_report(s: &mut Session, p: &Value) -> Result<Value> {
    crash::read(&dir, &id).map_err(EngineError::Params)
 }

+fn crash_reports_delete(s: &mut Session, p: &Value) -> Result<Value> {
+    let id = opt::<String>(p, "id")?;
+    let all = opt::<bool>(p, "all")?.unwrap_or(false);
+    let dir = crash_dir_for(s, p, Access::Write)?;
+    let deleted = match (id.as_deref(), all) {
+        (Some(id), false) => match crash::clear(&dir, Some(id)) {
+            0 => return Err(EngineError::Params(format!("no crash report `{}`", crash::limited(id, 64)))),
+            n => n,
+        },
+        (None, true) => crash::clear(&dir, None),
+        _ => return Err(EngineError::Params("give one of `id` (a crash report) or `all: true`".into())),
+    };
+    Ok(json!({"deleted": deleted}))
+}
+
 /// The draft input for `p` from the session: its commands and model (when shared), or a crash
 /// report's replay and model.
 pub fn bug_report_input(s: &Session, p: &Value) -> Result<bug_report::Input> {
@@ -131,3 +160,39 @@ fn crash_test(_: &mut Session, p: &Value) -> Result<Value> {
        _ => Err(EngineError::invalid("mode", "must be panic, recovered or abort")),
    }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// `diagnostics.crash_reports.delete` deletes one report by id, then the rest; an unknown or
+    /// hostile id and a missing choice are errors that delete nothing.
+    #[test]
+    fn crash_reports_are_deleted_one_or_all() {
+        let dir = std::env::temp_dir().join(format!("fieldcraft-crash-delete-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&dir);
+        let ids = ["20261014-101500-0000000000000001", "20261014-101600-0000000000000002", "20261014-101700-0000000000000003"];
+        for id in ids {
+            std::fs::create_dir_all(dir.join(id)).unwrap();
+            std::fs::write(dir.join(id).join("report.json"), r#"{"kind": "panic", "message": "x"}"#).unwrap();
+        }
+        let mut s = Session::default();
+        let d = dir.to_string_lossy().to_string();
+        let listed = |s: &mut Session| s.execute("diagnostics.crash_reports", &json!({"dir": d})).unwrap()["reports"].as_array().map_or(0, Vec::len);
+        assert_eq!(listed(&mut s), 3);
+        for bad in [
+            json!({"dir": d}),
+            json!({"dir": d, "id": "../x"}),
+            json!({"dir": d, "id": "20261014-101500-00000000000000ff"}),
+            json!({"dir": d, "id": ids[0], "all": true}),
+        ] {
+            assert!(s.execute("diagnostics.crash_reports.delete", &bad).is_err(), "{bad}");
+        }
+        assert_eq!(listed(&mut s), 3);
+        assert_eq!(s.execute("diagnostics.crash_reports.delete", &json!({"dir": d, "id": ids[1]})).unwrap()["deleted"], 1);
+        assert_eq!(listed(&mut s), 2);
+        assert_eq!(s.execute("diagnostics.crash_reports.delete", &json!({"dir": d, "all": true})).unwrap()["deleted"], 2);
+        assert_eq!(listed(&mut s), 0);
+        let _ = std::fs::remove_dir_all(&dir);
+    }
+}
@@ -0,0 +1,515 @@
+//! `mesh.hex.extrude`: hexahedra from a quad section up to a target surface
+//! ([`fieldcraft_mesh::hex::extrude_to_surface`]).
+//!
+//! The section is, in this order: the quadrilaterals of a set (`source_set`: shell elements or
+//! element faces); the mesh already on the source faces (element faces tagged with them, or the
+//! boundary faces of a neighbouring body's mesh lying on them), whose nodes the extrusion shares
+//! so it conforms with that mesh; or a fresh quad mesh of a planar source face. Target and side
+//! faces are projected onto through the trimmed B-rep projection that projection blocking uses
+//! ([`fieldcraft_mesh::tet::geometry::Tessellation::project_trimmed`]): exact on analytic faces,
+//! the tessellation's accuracy on free-form ones.
+
+use std::collections::BTreeMap;
+
+use fieldcraft_geometry::{FaceSurface, Shape};
+use fieldcraft_mesh::hex::{ExtrudeLayers, ExtrudePath, ExtrudeRole, ExtrudeSpec, MAX_BIAS, MAX_LAYERS, extrude_to_surface};
+use fieldcraft_mesh::planar::{face_boundary, mesh_region};
+use fieldcraft_mesh::project::Geometry;
+use fieldcraft_mesh::surface::{BoundarySurface, SurfaceOptions};
+use fieldcraft_mesh::tet::geometry::Tessellation;
+use fieldcraft_model::{ElementKind, Entity, GeometryRef, Model};
+use serde_json::{Value, json};
+
+use crate::requirement::Requirement;
+use crate::schema::ProblemKind;
+use crate::{CommandKind, CommandSpec, EngineError, Result, Session};
+
+pub const HEX_EXTRUDE: CommandSpec = CommandSpec {
+    id: "mesh.hex.extrude",
+    label: "Extrude to Surface",
+    params: r#"{"source": [{"body": "Post", "face": "F1"}] (the section: faces already meshed, by this body or a neighbour, or one planar face meshed here) or "source_set": "Section" (a set of quad shell elements or element faces, such as a 2D mesh), "to_surface": [{"body": "Wall", "face": "F7"}] (the target faces the last layer lies on), "sides": [{"body": "Post", "face": "F3"}, …] (optional: the faces the section's sides follow), "direction": [0, 0, 1] or "normal": true (each node along the section's normal toward the target; the default), "layers": 8 or "size": 2.0 (layer thickness, mm; also the size of a section meshed here; default 1/25 of the paths' extent), "bias": 1.0 (last layer's thickness over the first's, 0.001 to 1000), "body": "Post" (the body the elements fill; default: the first source face's body), "tolerance": 0.05 (chordal tolerance of the tessellation, mm; default 1e-3 of each body's diagonal)} — replaces `body`'s mesh with hex8 layers stacked on the section, each node along its own straight path, the last layer on the target surface; with `sides`, every layer's boundary nodes lie on the side faces (which need not be straight) and the interior follows them. A section taken from an existing mesh keeps its nodes, so the extrusion conforms with the neighbour across it. Boundary element faces are tagged with `body`'s source, target and side faces. Reports the layers, counts, quality, the target gap and where the section came from; a path that misses the target, or elements that would invert, is an error that says where"#,
+    form: Some(super::forms::HEX_EXTRUDE),
+    kind: CommandKind::Model,
+    requires: &[Requirement::Design],
+    run: hex_extrude,
+};
+
+/// Most faces in `source`, `to_surface` or `sides`.
+const MAX_FACES: usize = 1000;
+/// Default layer size and chordal tolerance, relative to the extent.
+const DEFAULT_RELATIVE_SIZE: f64 = 1.0 / 25.0;
+const DEFAULT_RELATIVE_TOLERANCE: f64 = 1e-3;
+const MIN_RELATIVE_TOLERANCE: f64 = 1e-5;
+/// Most quadrilaterals of a section meshed here.
+const MAX_SECTION_QUADS: usize = 1_000_000;
+
+/// The bodies the extrusion's faces lie on, and every face it names, with one projection.
+struct Faces {
+    bodies: Vec<Tessellation>,
+    /// Per body: its name, and its faces' names.
+    names: Vec<(String, Vec<String>)>,
+    /// Face id → (body, B-rep face).
+    faces: Vec<(usize, u32)>,
+    /// The largest chordal tolerance used.
+    tolerance: f64,
+}
+
+impl Geometry for Faces {
+    fn project(&self, face: u32, p: [f64; 3]) -> Option<[f64; 3]> {
+        let &(b, f) = self.faces.get(face as usize)?;
+        self.bodies.get(b)?.project_trimmed(f, p)
+    }
+    fn normal(&self, face: u32, p: [f64; 3]) -> Option<[f64; 3]> {
+        let &(b, f) = self.faces.get(face as usize)?;
+        self.bodies.get(b)?.face_normal(f, p)
+    }
+}
+
+impl Faces {
+    /// The ids of the faces `refs` names (a name selects all its pieces), loading their bodies.
+    fn add(&mut self, s: &Session, refs: &[GeometryRef], tolerance: Option<f64>, key: &str) -> Result<Vec<u32>> {
+        let design = s.design.as_deref().ok_or_else(|| EngineError::Params("open a design first".into()))?;
+        let mut out = Vec::new();
+        for r in refs {
+            if !matches!(r.entity, Entity::Face(_)) {
+                return Err(EngineError::invalid(key, format!("{r} is not a face")));
+            }
+            let shape = design.body(&r.body).ok_or_else(|| EngineError::invalid(key, format!("no body `{}`", r.body)))?;
+            let b = match self.names.iter().position(|(n, _)| *n == shape.name) {
+                Some(b) => b,
+                None => self.load(shape, tolerance)?,
+            };
+            let names = self.names.get(b).map(|(_, f)| f.clone()).unwrap_or_default();
+            let before = out.len();
+            for (i, name) in names.iter().enumerate() {
+                if r.selects(&GeometryRef::face(shape.name.as_str(), name.as_str())?) {
+                    let id = self.id(b, i as u32);
+                    if !out.contains(&id) {
+                        out.push(id);
+                    }
+                }
+            }
+            if out.len() == before {
+                return Err(EngineError::invalid(key, format!("body `{}` has no face `{}`", r.body, r.entity.name().unwrap_or_default())));
+            }
+        }
+        Ok(out)
+    }
+
+    fn load(&mut self, shape: &Shape, tolerance: Option<f64>) -> Result<usize> {
+        let diag = shape.size()?;
+        let tol = tolerance.unwrap_or(DEFAULT_RELATIVE_TOLERANCE * diag);
+        if tol < MIN_RELATIVE_TOLERANCE * diag {
+            return Err(EngineError::Params(format!("`tolerance` must be at least {} mm for body `{}`", MIN_RELATIVE_TOLERANCE * diag, shape.name)));
+        }
+        let mesh = shape.tessellate(tol)?;
+        let surface = BoundarySurface::new(
+            &mesh.positions,
+            &mesh.triangles,
+            &mesh.tri_face,
+            &SurfaceOptions { weld_distance: mesh.weld_distance, ..SurfaceOptions::default() },
+        )
+        .map_err(|e| EngineError::Params(format!("body `{}`: {e}", shape.name)))?;
+        self.bodies.push(Tessellation::new(&surface, super::mesh::analytic_surfaces(shape)));
+        self.names.push((shape.name.clone(), shape.faces().iter().map(|f| f.name.clone()).collect()));
+        self.tolerance = self.tolerance.max(tol);
+        Ok(self.bodies.len() - 1)
+    }
+
+    fn id(&mut self, b: usize, f: u32) -> u32 {
+        match self.faces.iter().position(|x| *x == (b, f)) {
+            Some(i) => i as u32,
+            None => {
+                self.faces.push((b, f));
+                (self.faces.len() - 1) as u32
+            }
+        }
+    }
+
+    /// The body and face name of face `id`.
+    fn name(&self, id: u32) -> Option<(&str, &str)> {
+        let &(b, f) = self.faces.get(id as usize)?;
+        let (body, faces) = self.names.get(b)?;
+        Some((body.as_str(), faces.get(f as usize)?.as_str()))
+    }
+}
+
+/// The section: node coordinates, the model label of each node it shares (none for a fresh
+/// section), and its quadrilaterals.
+struct Section {
+    nodes: Vec<[f64; 3]>,
+    labels: Vec<Option<u32>>,
+    quads: Vec<[u32; 4]>,
+    from: &'static str,
+}
+
+impl Section {
+    /// A section of model nodes: each label once, in order of first use.
+    fn of_labels(model: &Model, quads: &[[u32; 4]], from: &'static str) -> Result<Section> {
+        let mut index: BTreeMap<u32, u32> = BTreeMap::new();
+        let mut s = Section { nodes: Vec::new(), labels: Vec::new(), quads: Vec::with_capacity(quads.len()), from };
+        for q in quads {
+            let mut local = [0u32; 4];
+            for (slot, &l) in local.iter_mut().zip(q) {
+                *slot = match index.get(&l) {
+                    Some(&i) => i,
+                    None => {
+                        let xyz = model.nodes().get(&l).map(|n| n.xyz).ok_or_else(|| EngineError::Params(format!("node {l} is not in the model")))?;
+                        let i = s.nodes.len() as u32;
+                        s.nodes.push(xyz);
+                        s.labels.push(Some(l));
+                        index.insert(l, i);
+                        i
+                    }
+                };
+            }
+            s.quads.push(local);
+        }
+        Ok(s)
+    }
+}
+
+/// The four corners of element `e`'s face `face` (1-based), when it is a quadrilateral.
+fn quad_face(model: &Model, e: u32, face: u8) -> Option<[u32; 4]> {
+    let el = model.elements().get(&e)?;
+    let local = el.kind.faces().get(usize::from(face).checked_sub(1)?)?;
+    if local.len() < 4 || (local.len() != 4 && local.len() != 8) {
+        return None;
+    }
+    let corner = |k: usize| local.get(k).and_then(|&i| el.nodes.get(i)).copied();
+    Some([corner(0)?, corner(1)?, corner(2)?, corner(3)?])
+}
+
+/// The corners of a quad shell element.
+fn quad_shell(model: &Model, e: u32) -> Option<[u32; 4]> {
+    let el = model.elements().get(&e)?;
+    if !matches!(el.kind, ElementKind::Quad4 | ElementKind::Quad8) {
+        return None;
+    }
+    Some([*el.nodes.first()?, *el.nodes.get(1)?, *el.nodes.get(2)?, *el.nodes.get(3)?])
+}
+
+/// The elements of `body`'s mesh.
+fn body_elements(model: &Model, body: &str) -> std::collections::BTreeSet<u32> {
+    model.body_elements(body).into_iter().collect()
+}
+
+/// The quadrilaterals tagged with the faces `refs` names (shell elements filling them, element
+/// faces on them), leaving out `exclude`'s elements.
+fn tagged_quads(model: &Model, refs: &[GeometryRef], exclude: &std::collections::BTreeSet<u32>) -> Result<Vec<[u32; 4]>> {
+    let c = model.classification();
+    let mut tags: Vec<u32> = refs.iter().flat_map(|r| c.tags_selected_by(r)).collect();
+    tags.sort_unstable();
+    tags.dedup();
+    let mut out = Vec::new();
+    for (&e, t) in c.elements() {
+        if exclude.contains(&e) {
+            continue;
+        }
+        if t.region.is_some_and(|r| tags.binary_search(&r).is_ok()) {
+            out.push(quad_shell(model, e).ok_or_else(|| EngineError::Params(format!("element {e} on the source face is not a quadrilateral")))?);
+        }
+        for (&f, tag) in &t.faces {
+            if tags.binary_search(tag).is_ok() {
+                out.push(
+                    quad_face(model, e, f)
+                        .ok_or_else(|| EngineError::Params(format!("element {e}'s face {f} on the source face is not a quadrilateral")))?,
+                );
+            }
+        }
+    }
+    Ok(out)
+}
+
+/// The boundary faces of other bodies' meshes (tagged faces) that lie on the source faces.
+fn neighbour_quads(model: &Model, geometry: &Faces, source: &[u32], exclude: &std::collections::BTreeSet<u32>) -> Vec<[u32; 4]> {
+    let tol = 10.0 * geometry.tolerance.max(1e-9);
+    let on = |p: [f64; 3]| {
+        source.iter().any(|&f| geometry.project(f, p).is_some_and(|q| (0..3).map(|k| (q[k] - p[k]).powi(2)).sum::<f64>().sqrt() <= tol))
+    };
+    let xyz = |l: u32| model.nodes().get(&l).map(|n| n.xyz);
+    let mut out = Vec::new();
+    for (&e, t) in model.classification().elements() {
+        if exclude.contains(&e) {
+            continue;
+        }
+        for &f in t.faces.keys() {
+            let Some(q) = quad_face(model, e, f) else { continue };
+            let Some(pts) = q.iter().map(|&l| xyz(l)).collect::<Option<Vec<_>>>() else { continue };
+            let centre = pts.iter().fold([0.0; 3], |a, p| [a[0] + p[0] / 4.0, a[1] + p[1] / 4.0, a[2] + p[2] / 4.0]);
+            if pts.iter().all(|p| on(*p)) && on(centre) {
+                out.push(q);
+            }
+        }
+    }
+    out
+}
+
+/// A quad mesh of one planar face of `shape` of about `size`.
+fn mesh_planar_face(shape: &Shape, face: u32, size: f64, tolerance: f64) -> Result<Section> {
+    let surfaces = shape.face_surfaces()?;
+    let Some(Some(FaceSurface::Plane { normal, point })) = surfaces.get(face as usize).copied() else {
+        return Err(EngineError::Params(format!(
+            "the source face of body `{}` is not meshed and not planar: mesh it first (a 2D mesh, or a neighbouring body's mesh)",
+            shape.name
+        )));
+    };
+    let n = unit(normal).ok_or_else(|| EngineError::Params("the source face has no normal".into()))?;
+    let t = if n[0].abs() < 0.9 { [1.0, 0.0, 0.0] } else { [0.0, 1.0, 0.0] };
+    let u = unit(cross(n, t)).ok_or_else(|| EngineError::Params("the source face has no normal".into()))?;
+    let v = cross(n, u);
+    let dot = |a: [f64; 3], b: [f64; 3]| a[0] * b[0] + a[1] * b[1] + a[2] * b[2];
+    let mesh = shape.tessellate(tolerance)?;
+    // The tessellation in the face's frame, the face at z = 0.
+    let local: Vec<[f64; 3]> = mesh
+        .positions
+        .iter()
+        .map(|p| {
+            let d = [p[0] - point[0], p[1] - point[1], p[2] - point[2]];
+            [dot(d, u), dot(d, v), dot(d, n)]
+        })
+        .collect();
+    let boundary = face_boundary(&local, &mesh.triangles, &mesh.tri_face, face, mesh.weld_distance.max(tolerance))?;
+    let opts = fieldcraft_mesh::quad::QuadOptions { max_elements: MAX_SECTION_QUADS, ..Default::default() };
+    let m = mesh_region(&boundary.loops, ElementKind::Quad4, size, &opts)?;
+    let at = |xy: [f64; 2]| [0, 1, 2].map(|k| point[k] + xy[0] * u[k] + xy[1] * v[k]);
+    let nodes: Vec<[f64; 3]> = m.nodes.iter().map(|xy| at(*xy)).collect();
+    let quads = m
+        .elements
+        .iter()
+        .map(|e| match e.as_slice() {
+            [a, b, c, d, ..] => Ok([*a, *b, *c, *d]),
+            _ => Err(EngineError::Params("the section mesher made an element that is not a quadrilateral".into())),
+        })
+        .collect::<Result<Vec<_>>>()?;
+    Ok(Section { labels: vec![None; nodes.len()], nodes, quads, from: "meshed" })
+}
+
+fn unit(a: [f64; 3]) -> Option<[f64; 3]> {
+    let l = (a[0] * a[0] + a[1] * a[1] + a[2] * a[2]).sqrt();
+    (l > 0.0 && l.is_finite()).then(|| a.map(|x| x / l))
+}
+
+fn cross(a: [f64; 3], b: [f64; 3]) -> [f64; 3] {
+    [a[1] * b[2] - a[2] * b[1], a[2] * b[0] - a[0] * b[2], a[0] * b[1] - a[1] * b[0]]
+}
+
+/// A list of face references.
+fn face_refs(p: &Value, key: &str, required: bool) -> Result<Vec<GeometryRef>> {
+    let refs: Vec<GeometryRef> = match p.get(key) {
+        None if !required => return Ok(Vec::new()),
+        None => return Err(EngineError::param(key, ProblemKind::Required)),
+        Some(v) => serde_json::from_value(v.clone()).map_err(|e| EngineError::invalid(key, format!("a list of {{\"body\", \"face\"}}: {e}")))?,
+    };
+    if refs.len() > MAX_FACES || (required && refs.is_empty()) {
+        return Err(EngineError::invalid(key, format!("1 to {MAX_FACES} faces")));
+    }
+    Ok(refs)
+}
+
+/// The body the elements fill: `body`, or the first source face's.
+pub(super) fn extrude_body(_: &Session, p: &Value) -> Result<Vec<String>> {
+    if let Some(b) = p.get("body") {
+        let name = b.as_str().ok_or_else(|| EngineError::param("body", ProblemKind::NotAName))?;
+        GeometryRef::body(name)?;
+        return Ok(vec![name.to_string()]);
+    }
+    let source = face_refs(p, "source", false)?;
+    let first = source.first().ok_or_else(|| EngineError::Params("give `body` (the body the elements fill) with `source_set`".into()))?;
+    Ok(vec![first.body.clone()])
+}
+
+fn hex_extrude(s: &mut Session, p: &Value) -> Result<Value> {
+    let tolerance = super::hex::number(p, "tolerance")?;
+    let size = super::hex::number(p, "size")?;
+    let layers = match p.get("layers") {
+        None => None,
+        Some(v) => Some(
+            v.as_u64()
+                .filter(|n| (1..=MAX_LAYERS as u64).contains(n))
+                .ok_or_else(|| EngineError::invalid("layers", format!("a whole number from 1 to {MAX_LAYERS}")))? as usize,
+        ),
+    };
+    let bias = match p.get("bias") {
+        None => 1.0,
+        Some(v) => v
+            .as_f64()
+            .filter(|b| (1.0 / MAX_BIAS..=MAX_BIAS).contains(b))
+            .ok_or_else(|| EngineError::invalid("bias", format!("a number from {} to {MAX_BIAS}", 1.0 / MAX_BIAS)))?,
+    };
+    let path = match (p.get("direction"), p.get("normal")) {
+        (Some(d), None) => {
+            let d: [f64; 3] = serde_json::from_value(d.clone()).map_err(|_| EngineError::param("direction", ProblemKind::NotAVector { len: 3 }))?;
+            if !d.iter().all(|x| x.is_finite()) || unit(d).is_none() {
+                return Err(EngineError::invalid("direction", "a vector with a length"));
+            }
+            ExtrudePath::Direction(d)
+        }
+        (None, None) => ExtrudePath::Normal,
+        (None, Some(n)) => match n.as_bool() {
+            Some(true) => ExtrudePath::Normal,
+            _ => return Err(EngineError::invalid("normal", "true, or give `direction`")),
+        },
+        (Some(_), Some(_)) => return Err(EngineError::Params("give `direction` or `normal`, not both".into())),
+    };
+    let source = face_refs(p, "source", false)?;
+    let source_set = match p.get("source_set") {
+        None => None,
+        Some(v) => Some(v.as_str().ok_or_else(|| EngineError::param("source_set", ProblemKind::NotAName))?.to_string()),
+    };
+    if source.is_empty() == source_set.is_none() {
+        return Err(EngineError::Params("give the section as `source` (faces) or `source_set` (a set), one of them".into()));
+    }
+    let targets = face_refs(p, "to_surface", true)?;
+    let sides = face_refs(p, "sides", false)?;
+    let body = extrude_body(s, p)?.into_iter().next().unwrap_or_default();
+    let body_ref = GeometryRef::body(body.as_str())?;
+    let mut faces = Faces { bodies: Vec::new(), names: Vec::new(), faces: Vec::new(), tolerance: 0.0 };
+    let source_ids = faces.add(s, &source, tolerance, "source")?;
+    let target_ids = faces.add(s, &targets, tolerance, "to_surface")?;
+    let side_ids = faces.add(s, &sides, tolerance, "sides")?;
+    if let Some(f) = target_ids.iter().find(|f| source_ids.contains(f) || side_ids.contains(f)) {
+        let (b, n) = faces.name(*f).unwrap_or_default();
+        return Err(EngineError::Params(format!("face `{n}` of body `{b}` is both a target and a source or side face")));
+    }
+
+    // The section: a set, the mesh already on the source faces, or a fresh mesh of one face.
+    let own = body_elements(&s.model, &body);
+    let section = match &source_set {
+        Some(name) => {
+            let r = s.model.resolve_set(name)?;
+            let mut quads = Vec::new();
+            for &e in &r.elements {
+                if let Some(q) = quad_shell(&s.model, e) {
+                    quads.push(q);
+                }
+            }
+            for f in &r.faces {
+                quads.push(
+                    quad_face(&s.model, f.element, f.face).ok_or_else(|| {
+                        EngineError::Params(format!("set `{name}`: element {}'s face {} is not a quadrilateral", f.element, f.face))
+                    })?,
+                );
+            }
+            if quads.is_empty() {
+                return Err(EngineError::Params(format!("set `{name}` has no quadrilaterals (quad shell elements or hex element faces)")));
+            }
+            Section::of_labels(&s.model, &quads, "set")?
+        }
+        None => {
+            let tagged = tagged_quads(&s.model, &source, &own)?;
+            if !tagged.is_empty() {
+                Section::of_labels(&s.model, &tagged, "mesh")?
+            } else {
+                let near = neighbour_quads(&s.model, &faces, &source_ids, &own);
+                if !near.is_empty() {
+                    Section::of_labels(&s.model, &near, "neighbour")?
+                } else {
+                    let [id] = source_ids.as_slice() else {
+                        return Err(EngineError::Params("the source faces are not meshed: give one face to mesh here, or mesh them first".into()));
+                    };
+                    let (b, f) = faces.faces.get(*id as usize).copied().ok_or_else(|| EngineError::Params("no source face".into()))?;
+                    let name = faces.names.get(b).map(|n| n.0.clone()).unwrap_or_default();
+                    let shape = s.design.as_deref().and_then(|d| d.body(&name)).ok_or_else(|| EngineError::Params(format!("no body `{name}`")))?;
+                    let extent = shape.size()?;
+                    let h = size.unwrap_or(DEFAULT_RELATIVE_SIZE * extent);
+                    mesh_planar_face(shape, f, h, tolerance.unwrap_or(DEFAULT_RELATIVE_TOLERANCE * extent))?
+                }
+            }
+        }
+    };
+
+    let layers = match (layers, size) {
+        (Some(n), _) => ExtrudeLayers::Count(n),
+        (None, Some(h)) => ExtrudeLayers::Size(h),
+        (None, None) => {
+            let extent = s.design.as_deref().and_then(|d| d.body(&body)).map(Shape::size).transpose()?.unwrap_or(1.0);
+            ExtrudeLayers::Size(DEFAULT_RELATIVE_SIZE * extent)
+        }
+    };
+    let spec = ExtrudeSpec {
+        nodes: &section.nodes,
+        quads: &section.quads,
+        path,
+        targets: &target_ids,
+        sides: &side_ids,
+        layers,
+        bias,
+        tolerance: faces.tolerance.max(1e-9),
+        max_elements: fieldcraft_model::MAX_ELEMENTS / 8,
+    };
+    let m = extrude_to_surface(&spec, &faces).map_err(|e| EngineError::of_body(&body, e))?;
+
+    // Replace the body's mesh; the section's shared nodes stay.
+    let mut model = s.model.clone();
+    let cleared = super::replace::clear(&mut model, [body.as_str()]);
+    if let Some(l) = section.labels.iter().flatten().find(|l| !model.nodes().contains_key(l)) {
+        return Err(EngineError::Params(format!("the section's node {l} belongs to body `{body}`'s mesh, which the extrusion replaces")));
+    }
+    let n_src = section.nodes.len();
+    let fresh = m.nodes.len() - section.labels.iter().flatten().count();
+    let (first_node, first_element) = super::fresh_labels(&model, fresh, m.hexes.len())?;
+    let mut labels = Vec::with_capacity(m.nodes.len());
+    let mut next = first_node;
+    for (i, xyz) in m.nodes.iter().enumerate() {
+        let shared = if i < n_src { section.labels.get(i).copied().flatten() } else { None };
+        labels.push(match shared {
+            Some(l) => l,
+            None => {
+                model.set_node(next, *xyz)?;
+                next += 1;
+                next - 1
+            }
+        });
+    }
+    let body_tag = model.geometry_tag(&body_ref)?;
+    for (e, h) in m.hexes.iter().enumerate() {
+        let nodes: Vec<u32> = h.iter().map(|&i| labels.get(i as usize).copied().unwrap_or(0)).collect();
+        let l = first_element + e as u32;
+        model.set_element(l, ElementKind::Hex8, nodes)?;
+        model.tag_element(l, body_tag)?;
+    }
+    // Boundary faces on the body's own B-rep faces get their tags.
+    let source_own: Vec<u32> = source_ids.iter().copied().filter(|&f| faces.name(f).is_some_and(|(b, _)| b == body)).collect();
+    let mut tags: BTreeMap<u32, u32> = BTreeMap::new();
+    for b in &m.boundary {
+        let face = match b.role {
+            ExtrudeRole::Source => source_own.first().copied(),
+            ExtrudeRole::Target(f) | ExtrudeRole::Side(Some(f)) => Some(f),
+            ExtrudeRole::Side(None) => None,
+        };
+        let Some((owner, name)) = face.and_then(|f| faces.name(f)) else { continue };
+        if owner != body {
+            continue;
+        }
+        let key = face.unwrap_or_default();
+        let tag = match tags.get(&key) {
+            Some(&t) => t,
+            None => {
+                let t = model.geometry_tag(&GeometryRef::face(body.as_str(), name)?)?;
+                tags.insert(key, t);
+                t
+            }
+        };
+        model.tag_element_face(first_element + b.element, b.face, tag)?;
+    }
+    let (nodes, elements) = (model.nodes().len(), model.elements().len());
+    s.model = model;
+    let reply = json!({
+        "body": body,
+        "section": {"from": section.from, "quadrilaterals": section.quads.len(), "nodes": n_src, "shared_nodes": section.labels.iter().flatten().count()},
+        "layers": m.layers,
+        "kind": "hex8",
+        "elements": m.hexes.len(),
+        "new_nodes": fresh,
+        "quality": {"min_scaled_jacobian": m.min_scaled_jacobian, "mean_scaled_jacobian": m.mean_scaled_jacobian},
+        "volume": m.gate.volume,
+        "max_target_gap": m.max_target_gap,
+        "nodes": nodes,
+        "model_elements": elements,
+    });
+    Ok(cleared.report(s, reply))
+}
+
+#[cfg(test)]
+mod tests;
@@ -0,0 +1,185 @@
+use super::*;
+use crate::tests::{TempDir, design_file};
+
+fn open(commands: Value) -> (TempDir, Session) {
+    let bytes = fieldcraft_geometry::script_design(&json!({ "commands": commands }).to_string()).unwrap();
+    let (dir, path) = design_file(&bytes);
+    let mut s = Session::default();
+    s.execute("geometry.open", &json!({"path": path})).unwrap();
+    (dir, s)
+}
+
+/// A square post whose top is cut by a cylinder (axis X, radius 20, at z = 30), a square post
+/// whose top is a sphere cap (centre z = −5, radius 25), and a block under the first post.
+fn parts() -> (TempDir, Session) {
+    open(json!([
+        {"command": "solid.box", "params": {"corner": [-4, -4, 0], "length": 8, "width": 8, "height": 30, "body_name": "Post"}},
+        {"command": "solid.cylinder", "params": {"base": [-20, 0, 30], "axis": [1, 0, 0], "radius": 20, "height": 40, "body_name": "Bar", "operation": "new"}},
+        {"command": "solid.combine", "params": {"target": "Post", "tools": ["Bar"], "operation": "cut"}},
+        {"command": "solid.box", "params": {"corner": [-6, -6, 0], "length": 12, "width": 12, "height": 30, "body_name": "Dome", "operation": "new"}},
+        {"command": "solid.sphere", "params": {"center": [0, 0, -5], "radius": 25, "body_name": "Ball", "operation": "new"}},
+        {"command": "solid.combine", "params": {"target": "Dome", "tools": ["Ball"], "operation": "intersect"}},
+        {"command": "solid.box", "params": {"corner": [-4, -4, -10], "length": 8, "width": 8, "height": 10, "body_name": "Base", "operation": "new"}},
+    ]))
+}
+
+/// `{"body", "face"}` of each face of `body` whose surface `pick` accepts.
+fn faces(s: &Session, body: &str, pick: impl Fn(&FaceSurface) -> bool) -> Vec<Value> {
+    let b = s.design.as_deref().unwrap().body(body).unwrap();
+    b.faces()
+        .iter()
+        .zip(b.face_surfaces().unwrap())
+        .filter(|(_, f)| f.as_ref().is_some_and(&pick))
+        .map(|(f, _)| json!({"body": body, "face": f.name}))
+        .collect()
+}
+
+fn plane(n: [f64; 3]) -> impl Fn(&FaceSurface) -> bool {
+    move |f| matches!(f, FaceSurface::Plane { normal, .. } if (0..3).all(|k| (normal[k] - n[k]).abs() < 1e-9))
+}
+
+fn sides(s: &Session, body: &str) -> Vec<Value> {
+    faces(s, body, |f| matches!(f, FaceSurface::Plane { normal, .. } if normal[2].abs() < 1e-9))
+}
+
+/// The coordinates of the nodes on face `face` (through a set by geometry).
+fn nodes_on(s: &mut Session, name: &str, face: &Value) -> Vec<[f64; 3]> {
+    s.execute("model.set.create", &json!({"name": name, "geometry": [face]})).unwrap();
+    let r = s.model.resolve_set(name).unwrap();
+    r.nodes.iter().map(|n| s.model.nodes()[n].xyz).collect()
+}
+
+#[test]
+fn a_square_post_extrudes_up_to_a_cylinder() {
+    let (_d, mut s) = parts();
+    let bottom = faces(&s, "Post", plane([0.0, 0.0, -1.0]));
+    let top = faces(&s, "Post", |f| matches!(f, FaceSurface::Cylinder { .. }));
+    let r = s
+        .execute("mesh.hex.extrude", &json!({"source": bottom, "to_surface": top, "sides": sides(&s, "Post"), "direction": [0, 0, 1], "size": 1.0}))
+        .unwrap();
+    assert_eq!((r["body"].as_str(), r["section"]["from"].as_str()), (Some("Post"), Some("meshed")), "{r}");
+    assert_eq!(r["layers"], 10, "{r}");
+    let min_sj = r["quality"]["min_scaled_jacobian"].as_f64().unwrap();
+    assert!(min_sj >= 0.5, "{r}");
+    assert!(r["max_target_gap"].as_f64().unwrap() < 1e-6, "{r}");
+    // ∫∫ (30 − √(400 − y²)) dx dy over the 8 × 8 square.
+    let exact = 8.0 * (30.0 * 8.0 - (4.0 * 384.0f64.sqrt() + 400.0 * 0.2f64.asin()));
+    let volume = r["volume"].as_f64().unwrap();
+    assert!((volume - exact).abs() < 1e-3 * exact, "{volume} vs {exact}");
+    // Every node of the last layer is on the cylinder: the target faces are tagged.
+    let on = nodes_on(&mut s, "Top", &top[0]);
+    assert_eq!(on.len() as u64, r["section"]["nodes"].as_u64().unwrap(), "one node per section node");
+    for p in on {
+        let radius = (p[1].powi(2) + (p[2] - 30.0).powi(2)).sqrt();
+        assert!((radius - 20.0).abs() < 1e-6, "{p:?}: {radius}");
+    }
+    let q = s.execute("mesh.quality", &json!({})).unwrap();
+    assert_eq!(q["invalid"]["count"], 0, "{q}");
+}
+
+#[test]
+fn a_square_post_extrudes_up_to_a_sphere_cap_along_its_normal() {
+    let (_d, mut s) = parts();
+    let bottom = faces(&s, "Dome", plane([0.0, 0.0, -1.0]));
+    let cap = faces(&s, "Dome", |f| matches!(f, FaceSurface::Sphere { .. }));
+    let r = s
+        .execute("mesh.hex.extrude", &json!({"source": bottom, "to_surface": cap, "sides": sides(&s, "Dome"), "layers": 8, "bias": 0.5, "size": 1.5}))
+        .unwrap();
+    assert_eq!(r["layers"], 8, "{r}");
+    assert!(r["quality"]["min_scaled_jacobian"].as_f64().unwrap() >= 0.5, "{r}");
+    let on = nodes_on(&mut s, "Cap", &cap[0]);
+    assert!(on.len() > 50, "{}", on.len());
+    for p in on {
+        let radius = (p[0].powi(2) + p[1].powi(2) + (p[2] + 5.0).powi(2)).sqrt();
+        assert!((radius - 25.0).abs() < 1e-6, "{p:?}: {radius}");
+    }
+}
+
+#[test]
+fn the_extrusion_conforms_with_the_neighbour_it_starts_from() {
+    let (_d, mut s) = parts();
+    s.execute("mesh.hex.generate", &json!({"body": "Base", "size": 2.0})).unwrap();
+    let base_nodes = s.model.nodes().len();
+    let bottom = faces(&s, "Post", plane([0.0, 0.0, -1.0]));
+    let top = faces(&s, "Post", |f| matches!(f, FaceSurface::Cylinder { .. }));
+    let r = s
+        .execute("mesh.hex.extrude", &json!({"source": bottom, "to_surface": top, "sides": sides(&s, "Post"), "direction": [0, 0, 1], "size": 2.0}))
+        .unwrap();
+    assert_eq!(r["section"]["from"], "neighbour", "{r}");
+    assert_eq!(r["section"]["shared_nodes"], 25, "the base's 5 × 5 top nodes: {r}");
+    assert_eq!(s.model.nodes().len(), base_nodes + r["new_nodes"].as_u64().unwrap() as usize);
+    let d = s.execute("mesh.check.duplicates", &json!({})).unwrap();
+    assert_eq!((d["counts"]["coincident"].as_u64(), d["counts"]["cracks"].as_u64()), (Some(0), Some(0)), "{d}");
+    // The base keeps its mesh; extruding again replaces only the post's.
+    let base = s.model.body_elements("Base").len();
+    s.execute("mesh.hex.extrude", &json!({"source": bottom, "to_surface": top, "direction": [0, 0, 1], "layers": 3})).unwrap();
+    assert_eq!(s.model.body_elements("Base").len(), base);
+    assert_eq!(s.model.body_elements("Post").len(), 16 * 3);
+}
+
+#[test]
+fn a_2d_mesh_extrudes_from_its_set() {
+    let (_d, mut s) = parts();
+    s.execute("mesh.planar", &json!({"polygon": [[-3, -3], [3, -3], [3, 3], [-3, 3]], "size": 1.0, "name": "Plane"})).unwrap();
+    s.execute("model.set.create", &json!({"name": "Section", "geometry": [{"body": "Plane", "face": "area"}]})).unwrap();
+    let top = faces(&s, "Post", |f| matches!(f, FaceSurface::Cylinder { .. }));
+    let r = s.execute("mesh.hex.extrude", &json!({"source_set": "Section", "to_surface": top, "body": "Column", "layers": 5})).unwrap();
+    assert_eq!(r["section"]["from"], "set", "{r}");
+    let quads = r["section"]["quadrilaterals"].as_u64().unwrap() as usize;
+    assert_eq!(r["section"]["shared_nodes"], r["section"]["nodes"], "{r}");
+    assert_eq!(s.model.body_elements("Column").len(), quads * 5);
+    assert!(r["quality"]["min_scaled_jacobian"].as_f64().unwrap() >= 0.5, "{r}");
+}
+
+#[test]
+fn hostile_params_are_errors_and_change_nothing() {
+    let (_d, mut s) = parts();
+    let bottom = faces(&s, "Post", plane([0.0, 0.0, -1.0]));
+    let top = faces(&s, "Post", |f| matches!(f, FaceSurface::Cylinder { .. }));
+    let ok = json!({"source": bottom, "to_surface": top, "direction": [0, 0, 1], "layers": 2});
+    let with = |k: &str, v: Value| {
+        let mut p = ok.clone();
+        p[k] = v;
+        p
+    };
+    let without = |k: &str| {
+        let mut p = ok.clone();
+        p.as_object_mut().unwrap().remove(k);
+        p
+    };
+    let cases = [
+        without("to_surface"),
+        without("source"),
+        with("to_surface", json!([])),
+        with("to_surface", json!("F1")),
+        with("to_surface", json!([{"body": "Nope", "face": "F1"}])),
+        with("to_surface", json!([{"body": "Post", "face": "nope"}])),
+        with("to_surface", json!([{"body": "Post"}])),
+        with("to_surface", bottom.clone().into()),
+        with("source_set", json!("Nope")),
+        with("direction", json!([0, 0, 0])),
+        with("direction", json!([0, 0, -1])),
+        with("direction", json!([1, 0])),
+        with("direction", json!([f64::MAX, 0, 0])),
+        with("normal", json!(false)),
+        with("layers", json!(0)),
+        with("layers", json!(1e9)),
+        with("layers", json!(-3)),
+        with("bias", json!(0)),
+        with("bias", json!(1e9)),
+        with("bias", json!("x")),
+        with("size", json!(-1)),
+        with("tolerance", json!(1e-30)),
+        with("body", json!(7)),
+        with("sides", json!([{"body": "Dome", "face": "F4:-z"}])),
+        with("source", json!([{"body": "Post", "face": "F1:-x"}, {"body": "Post", "face": "F1:+x"}])),
+        // A curved face that is not meshed cannot be meshed here.
+        with("source", top.clone().into()),
+    ];
+    let before = s.model.clone();
+    for (i, p) in cases.iter().enumerate() {
+        assert!(s.execute("mesh.hex.extrude", p).is_err(), "case {i}: {p}");
+        assert_eq!(s.model, before, "case {i} changed the model");
+    }
+    assert!(s.execute("mesh.hex.extrude", &ok).is_ok());
+}
@@ -19,6 +19,16 @@ use fieldcraft_io::roots::{Access, Roots};
 use super::{file_param, req};
 use crate::{CommandKind, CommandSpec, EngineError, Result, Session, next_revision};

+pub const NEW: CommandSpec = CommandSpec {
+    id: "file.new",
+    label: "New Model",
+    params: r#"{} — starts an empty model in place of the current one: no design, mesh, definitions, results or journal; unsaved changes are discarded (the window asks first) and the undo history starts empty"#,
+    form: Some(&[]),
+    kind: CommandKind::Session,
+    requires: &[],
+    run: new_model,
+};
+
 pub const OPEN: CommandSpec = CommandSpec {
    id: "file.open",
    label: "Open Model",
@@ -89,6 +99,15 @@ pub const SAMPLE: CommandSpec = CommandSpec {
    run: open_sample,
 };

+fn new_model(s: &mut Session, _: &Value) -> Result<Value> {
+    let mut empty = Session::default();
+    // Nothing to save until a command changes it.
+    empty.saved_revision = Some(empty.revision);
+    empty.saved_view = empty.view.clone();
+    s.replace_with(empty);
+    Ok(summary(s, &[]))
+}
+
 fn open_sample(s: &mut Session, p: &Value) -> Result<Value> {
    let name: &str = req(p, "name")?;
    let names = || crate::sample::SAMPLES.iter().map(|x| x.name).collect::<Vec<_>>().join(", ");
@@ -106,6 +125,7 @@ fn open_sample(s: &mut Session, p: &Value) -> Result<Value> {
    // A sample just opened has nothing to save: it opens again the same way.
    opened.saved_revision = Some(opened.revision);
    opened.saved_view = opened.view.clone();
+    opened.sample = Some(sample.label);
    s.replace_with(opened);
    let mut reply = summary(s, &[]);
    reply["sample"] = json!(sample.name);
@@ -211,7 +231,12 @@ impl Session {
                }
            });
            if let Some(d) = &design {
-                warnings.extend(d.errors.iter().filter(|e| e.feature.starts_with("partition ")).map(|e| format!("{}: {}", e.feature, e.message)));
+                warnings.extend(
+                    d.errors
+                        .iter()
+                        .filter(|e| e.feature.starts_with("partition ") || e.feature.starts_with("merge "))
+                        .map(|e| format!("{}: {}", e.feature, e.message)),
+                );
            }
            sources.design = Some(source);
        }
@@ -221,7 +246,7 @@ impl Session {
            surfaces.extend(opened.into_iter().flatten().map(Arc::new));
            sources.meshes.push(source);
        }
-        let session = Session {
+        let mut session = Session {
            model: file.model,
            design,
            surfaces,
@@ -232,6 +257,8 @@ impl Session {
            view: file.view,
            ..Session::default()
        };
+        let (_, failed) = super::stitch::restitch(&mut session);
+        warnings.extend(failed.into_iter().map(|(n, why)| format!("stitch `{n}`: {why}")));
        (session, warnings)
    }

@@ -374,6 +401,19 @@ mod tests {
        s.execute("model.material.create", &json!({"name": "Steel", "elastic": {"type": "isotropic", "young": 210000.0, "poisson": 0.3}})).unwrap();
    }

+    /// `file.new` empties the model, its journal and its undo history, and has nothing to save.
+    #[test]
+    fn new_starts_an_empty_model() {
+        let mut s = Session::default();
+        s.execute("file.sample", &json!({"name": "cantilever"})).unwrap();
+        s.execute("mesh.node.add", &json!({"label": 10_000, "xyz": [0, 0, 0]})).unwrap();
+        let r = s.execute("file.new", &json!({})).unwrap();
+        assert_eq!((r["nodes"].as_u64(), r["elements"].as_u64(), r["journal"].as_u64()), (Some(0), Some(0), Some(0)), "{r}");
+        assert!(s.model.materials().is_empty() && s.model.steps().is_empty() && s.design.is_none() && s.sample.is_none());
+        assert!(!s.is_dirty(), "an empty model has nothing to save");
+        assert!(s.execute("edit.undo", &json!({})).is_err(), "the undo history starts empty");
+    }
+
    #[test]
    fn save_and_open_keep_the_model_journal_and_design() {
        let d = dir("roundtrip");
@@ -54,10 +54,18 @@ pub const SET: &[Field] = &[
    )
    .help("Bodies of the design, or their named faces, edges or vertices. Kept by name, so the set survives remeshing.")
    .hint("whole bodies, or their faces, edges or vertices"),
-    json("nodes", "Nodes").help("Mesh node labels, as a JSON list.").hint("[labels]"),
-    json("elements", "Elements").help("Mesh element labels, as a JSON list.").hint("[labels]"),
-    json("faces", "Element faces").help("Element faces, as a JSON list of element label and local face number.").hint("[{\"element\", \"face\"}]"),
-    json("edges", "Element edges").help("Element edges, as a JSON list of element label and local edge number.").hint("[{\"element\", \"edge\"}]"),
+    labels("nodes", "Nodes", LabelOf::Node).help("Mesh node labels; Use selection takes the picked nodes.").hint("labels: 1, 2, 10-20"),
+    labels("elements", "Elements", LabelOf::Element)
+        .help("Mesh element labels; Use selection takes the picked elements.")
+        .hint("labels: 1, 2, 10-20"),
+    sides("faces", "Element faces", Side::Face)
+        .help(
+            "Element faces as element:face (local face number), ranges of elements sharing one: 1-20:3, 25:1. Use selection takes the picked faces.",
+        )
+        .hint("element:face, e.g. 1-20:3, 25:1"),
+    sides("edges", "Element edges", Side::Edge)
+        .help("Element edges as element:edge (local edge number), ranges of elements sharing one: 1-20:3, 25:1.")
+        .hint("element:edge, e.g. 1-20:3"),
 ];

 const ELASTIC: Field = variants(
@@ -184,18 +192,19 @@ const HYPERELASTIC: Field = variants(
 .help("A large-strain rubber model (nonlinear steps), built on the isotropic constants.")
 .hint("large strain in nonlinear steps, from the isotropic constants");

+/// The material axes 1, 2, 3 (the global X, Y, Z until material orientations land).
+const AXES_123: &[&str] = &["1", "2", "3"];
+
 const THERMAL: Field = group(
    "thermal",
    "Thermal",
    &[
-        json("conductivity", "Conductivity")
-            .help("Thermal conductivity, one value or one per axis. Steel ≈ 50 W/(m·K), i.e. 50 in mm-t-s-N.")
-            .hint("k or [k1, k2, k3]"),
+        per_axis("conductivity", "Conductivity", D::Conductivity, Some(0.0), AXES_123)
+            .help("Thermal conductivity, one value or one per material axis. Steel ≈ 50 W/(m·K), i.e. 50 in mm-t-s-N."),
        positive("specific_heat", "Specific heat", D::SpecificHeat)
            .help("Heat that raises a unit mass by one degree. Steel ≈ 460 J/(kg·K), 4.6e8 in mm-t-s."),
-        json("expansion", "Expansion")
-            .help("Thermal expansion coefficient, one value or one per axis, in 1/K. Steel ≈ 1.2e-5, aluminium ≈ 2.3e-5.")
-            .hint("α or [α1, α2, α3], 1/K"),
+        per_axis("expansion", "Expansion", D::Expansion, None, AXES_123)
+            .help("Thermal expansion coefficient, one value or one per material axis. Steel ≈ 1.2e-5, aluminium ≈ 2.3e-5."),
        num("reference_temperature", "Reference temperature", D::Temperature).help("The temperature at which there is no thermal strain.").def("0"),
    ],
 )
@@ -351,9 +360,9 @@ pub const REFERENCE_POINT: &[Field] = &[
    int("label", "Node label", 0, u32::MAX as i64).help("The node label written to decks.").hint("0: the highest free label"),
 ];

-const DOFS: Field = json("dofs", "Degrees of freedom")
+const DOFS: Field = multi("dofs", "Degrees of freedom", &[("1", "UX"), ("2", "UY"), ("3", "UZ"), ("4", "URX"), ("5", "URY"), ("6", "URZ")])
    .help("Which of the six DOFs to couple (1–3 translations, 4–6 rotations); all when empty.")
-    .hint("[1, …, 6], default all");
+    .hint("all");

 pub const COUPLING: &[Field] = &[
    NAME,
@@ -369,7 +378,9 @@ pub const COUPLING: &[Field] = &[
 pub const MASS: &[Field] = &[
    NAME,
    TARGET,
-    positive("mass", "Mass", D::Mass).help("A lumped mass at each node of the target.").hint("per node; [mx, my, mz] in JSON"),
+    per_axis("mass", "Mass", D::Mass, Some(0.0), XYZ)
+        .help("A lumped mass at each node of the target: one value, or one per direction X, Y, Z.")
+        .hint("per node"),
    vector("inertia", "Inertia", D::Inertia, &["I11", "I22", "I33", "I12", "I13", "I23"])
        .help("Rotary inertia about the reference point: three moments and three products.")
        .hint("about the node; needs a reference point"),
@@ -579,6 +590,24 @@ const FACE_CONDITION: &[Variant] = &[
    variant("periodic", "Periodic", &[]),
 ];

+const BOX_FACE: Field =
+    choice("", "Box face", &[("x_min", "X min"), ("x_max", "X max"), ("y_min", "Y min"), ("y_max", "Y max"), ("z_min", "Z min"), ("z_max", "Z max")])
+        .help("A face of the domain's box, at the smallest or largest X, Y or Z.")
+        .req();
+const OBSTACLE_FACE_FIELDS: &[Field] = &[
+    reference("body", "Body", C::Body).help("An obstacle body of the design.").req(),
+    text("face", "Face").help("A persistent face name of the body (e.g. F3); it also selects the face's split pieces.").req(),
+];
+const OBSTACLE_FACE: Field = group("face", "Face", OBSTACLE_FACE_FIELDS).help("The obstacle face.").req();
+const SURFACE_CONDITION: &[Variant] = &[
+    variant("wall", "Wall at rest", &[]),
+    variant(
+        "moving_wall",
+        "Moving wall",
+        &[xyz("velocity", "Velocity", D::Velocity).help("The wall's tangential velocity; the body itself does not move.").req()],
+    ),
+];
+
 const fn face(key: &'static str, label: &'static str) -> Field {
    variants(key, label, FACE_CONDITION).hint("wall")
 }
@@ -605,9 +634,16 @@ pub const FLUID_DOMAIN: &[Field] = &[
    )
    .help("The condition on each face of the box."),
    references("obstacles", "Obstacles", C::Body).help("Bodies of the design the flow goes around."),
-    json("surfaces", "Obstacle faces")
-        .help("Conditions on single obstacle faces, as JSON; walls by default.")
-        .hint("[{\"face\", \"condition\"}]; walls by default"),
+    rows(
+        "surfaces",
+        "Obstacle faces",
+        &[
+            OBSTACLE_FACE,
+            variants("condition", "Condition", SURFACE_CONDITION).help("The flow condition on that face.").req().def(r#"{"type": "wall"}"#),
+        ],
+    )
+    .help("Conditions on single obstacle faces; every other obstacle face is a wall at rest.")
+    .hint("walls by default"),
    xyz("initial_velocity", "Initial velocity", D::Velocity).help("The fluid's velocity at the start."),
    xyz("acceleration", "Acceleration", D::Acceleration).help("A body acceleration on the fluid, such as gravity."),
    positive("tolerance", "Obstacle tolerance", D::Length)
@@ -617,11 +653,10 @@ pub const FLUID_DOMAIN: &[Field] = &[

 pub const FLUID_BOUNDARY: &[Field] = &[
    reference("domain", "Domain", C::FluidDomain).help("The fluid domain to change.").req(),
-    json("at", "Boundary")
-        .help("A box face (x_min … z_max) or an obstacle face, as JSON.")
+    name_or("at", "Boundary", &BOX_FACE, "Obstacle face", OBSTACLE_FACE_FIELDS)
+        .help("A face of the domain's box, or a named face of an obstacle body.")
        .req()
-        .def("\"x_min\"")
-        .hint("\"x_min\" … \"z_max\", or {\"body\", \"face\"}"),
+        .def("\"x_min\""),
    variants("condition", "Condition", FACE_CONDITION).help("The flow condition on that boundary.").req().def(r#"{"type": "velocity"}"#),
 ];

@@ -659,9 +694,9 @@ const PROCEDURE: Field = variants(
                flag("line_search", "Line search")
                    .help("Scale each Newton correction to reduce the residual; helps with hard convergence.")
                    .def("false"),
-                json("load_path", "Load path")
-                    .help("How the load factor varies through the step, as JSON pairs of step fraction and factor; a linear ramp when empty.")
-                    .hint("[[fraction, factor], …]; a ramp when empty"),
+                table("load_path", "Load path", D::None, &["fraction", "factor"], fieldcraft_model::MAX_LOAD_PATH_POINTS)
+                    .help("How the load factor varies through the step: rows of step fraction (0 to 1) and load factor; a linear ramp when empty.")
+                    .hint("a ramp when empty"),
                group(
                    "imperfection",
                    "Imperfection",
@@ -682,9 +717,18 @@ const PROCEDURE: Field = variants(
                            .help("Cylindrical: displacements only. Spherical: displacements and load factor.")
                            .def("\"cylindrical\""),
                        positive("max_load_factor", "Max load factor", D::None).help("Stop when the load factor reaches this.").def("1"),
-                        json("displacement_limit", "Displacement limit")
-                            .help("Stop when a node's displacement reaches a value, as JSON.")
-                            .hint("{\"node\": 1, \"direction\": 3, \"displacement\": -10}"),
+                        group(
+                            "displacement_limit",
+                            "Displacement limit",
+                            &[
+                                int("node", "Node", 1, u32::MAX as i64).help("The label of the node watched.").req(),
+                                int("direction", "Direction", 1, 3).help("1, 2, 3: its translation along X, Y, Z.").req().def("3"),
+                                num("displacement", "Displacement", D::Length)
+                                    .help("The step stops when that translation reaches this size (its sign is ignored).")
+                                    .req(),
+                            ],
+                        )
+                        .help("Stop when a node's displacement reaches a value; at the max load factor when empty."),
                    ],
                )
                .help("Follow the load-displacement path through limit points (snap-through), with the load factor as an unknown."),
@@ -809,9 +853,20 @@ const PROCEDURE: Field = variants(
 )
 .help("What the step solves: linear or nonlinear static, buckling, frequencies, explicit dynamics, heat transfer or flow.");

-const OUTPUT: Field = json("output", "Output")
-    .help("Which results to keep, as JSON; by procedure when empty.")
-    .hint("[\"displacement\", \"stress\", …]; by procedure when empty");
+const OUTPUT: Field = multi(
+    "output",
+    "Output",
+    &[
+        ("\"displacement\"", "Displacement"),
+        ("\"reaction_force\"", "Reaction force"),
+        ("\"stress\"", "Stress"),
+        ("\"strain\"", "Strain"),
+        ("\"temperature\"", "Temperature"),
+        ("\"heat_flux\"", "Heat flux"),
+    ],
+)
+.help("Which results to keep; by procedure when none is ticked.")
+.hint("by procedure");
 const STEP_BCS: Field =
    references("boundary_conditions", "Boundary conditions", C::BoundaryCondition).help("The boundary conditions active in the step.");
 const STEP_LOADS: Field = references("loads", "Loads", C::Load).help("The loads active in the step.");
@@ -834,6 +889,43 @@ pub const STEP_ACTIVATE: &[Field] = &[
    flag("active", "Active").help("On: they act in the step. Off: they are switched off from it on.").def("true"),
 ];

+pub const DATUM_SUPPRESS: &[Field] = &[
+    reference("name", "Datum", C::Datum).help("The datum to keep but leave out of the model.").req(),
+    flag("suppressed", "Suppressed").help("On: left out (its partitions stop cutting). Off: back in the model.").def("true"),
+];
+
+pub const PARTITION_SUPPRESS: &[Field] = &[
+    reference("name", "Partition", C::Partition).help("The partition to keep but leave out: its cells merge back.").req(),
+    flag("suppressed", "Suppressed").help("On: the design is cut without it. Off: it cuts again.").def("true"),
+];
+
+pub const RENAME: &[Field] = &[
+    choice(
+        "kind",
+        "Kind",
+        &[
+            ("set", "Set"),
+            ("material", "Material"),
+            ("section", "Section"),
+            ("step", "Step"),
+            ("boundary_condition", "Boundary condition"),
+            ("load", "Load"),
+            ("reference_point", "Reference point"),
+            ("coupling", "Coupling"),
+            ("contact", "Contact"),
+            ("tie", "Tie"),
+            ("point_mass", "Point mass"),
+            ("spring", "Spring"),
+            ("fluid_domain", "Fluid domain"),
+            ("datum", "Datum"),
+        ],
+    )
+    .help("What kind of definition to rename.")
+    .req(),
+    text("from", "Name").help("Its current name.").req(),
+    text("to", "New name").help("Every definition that refers to it is changed to the new name.").req(),
+];
+
 pub const UNITS: &[Field] = &[choice(
    "system",
    "Unit system",
@@ -1050,10 +1142,22 @@ pub const HEX_BLOCKS: &[Field] = &[
    FEATURE_ANGLE,
 ];

+const CELL_METHODS: &[(&str, &str)] = &[
+    ("auto", "Auto (hex, else tet)"),
+    ("hex", "Hex"),
+    ("swept", "Swept"),
+    ("extrude", "Extrude"),
+    ("sweep", "Sweep"),
+    ("revolve", "Revolve"),
+    ("mapped", "Mapped"),
+    ("tet", "Tet"),
+];
+
 pub const CELLS: &[Field] = &[
-    json("methods", "Methods")
-        .help("The meshing method per cell, as JSON.")
-        .hint(r#"{"cell": "auto | hex | swept | extrude | sweep | revolve | mapped | tet"}"#),
+    references("bodies", "Cells", C::Body)
+        .help("The cells (bodies) to mesh: tick them, or pick them in the viewport (Select: Bodies) and Use selection. Every body of the design when none is ticked.")
+        .hint("every body of the design"),
+    ref_choices("methods", "Methods", C::Body, CELL_METHODS).help("A meshing method for single cells; the others take Other cells' method."),
    choice(
        "default",
        "Other cells",
@@ -1062,21 +1166,72 @@ pub const CELLS: &[Field] = &[
    .help("The method for cells not listed in Methods. All hex meshes every cell as a mapped block, with the division counts of all cells assigned together so shared faces match (mesh.hex.blocks).")
    .notes(&[("blocks", "All hex: every cell must have six sides, each with four edges; leave Methods empty.")])
        .def("\"auto\""),
-    references("bodies", "Cells", C::Body).help("The cells (bodies) to mesh; every body of the design when empty.").hint("every body of the design"),
    HEX_SIZE,
    HEX_ORDER,
    TOLERANCE,
+    choice("transition", "Hex–tet joint", &[("pyramid", "Pyramids (conforming)"), ("tie", "Tie")])
+        .help("How a tet cell meets the hex cells across its partitions: a layer of pyramids on the hex faces, one conforming mesh (linear elements), or a tie between the two meshes.")
+        .def("\"pyramid\""),
+];
+
+pub const HEX_PROJECT: &[Field] = &[
+    reference("body", "Body", C::Body).help("The body to mesh with a projected block topology.").req(),
+    HEX_SIZE,
+    choice(
+        "template",
+        "Template",
+        &[("grid", "Block grid (carve)"), ("sphere", "Sphere (7 blocks)"), ("butterfly", "Butterfly (5-block disc, extruded)"), ("blocks", "Blocks (given vertices)")],
+    )
+    .help("The block topology projected onto the body: a grid of blocks you may carve, the seven-block sphere, the five-block butterfly for round sections, or blocks you list.")
+    .def("\"grid\""),
+    xyz("center", "Centre", POINT).help("Sphere or butterfly centre.").hint("from the body's bounding box"),
+    positive("radius", "Radius", D::Millimetre).help("Sphere or butterfly radius.").hint("from the body"),
+    xyz("axis", "Axis", D::None).help("Butterfly axis direction.").hint("0, 0, 1"),
+    json("levels", "Levels")
+        .help("Sphere and butterfly levels; for a butterfly, distances along the axis from the centre, as JSON.")
+        .hint("[z0, z1, ...]; from the bounding box"),
+    range("inset", "Inset", D::None, 0.05, 0.95).help("Inner square or cube corner at this fraction of the radius.").def("0.55"),
+    json("grid", "Grid").help("The block grid: planes per axis or a cell count, and blocks to carve away, as JSON.").hint(r#"{"cells": [ni, nj, nk], "carve": [{"i": [a, b], "j": [c, d], "k": [e, f]}]}"#),
+    json("blocks", "Blocks").help("Template Blocks: vertices and hex8 blocks, as JSON.").hint(r#"{"vertices": [[x, y, z], ...], "blocks": [[v1..v8], ...]}"#),
+    json("operations", "Operations").help("O-grids, extrusions, connections, removals and merges applied in order, as JSON.").hint(r#"[{"op": "o_grid", "block": 0, "open": ["+z"]}]"#),
+    json("faces", "Face targets").help("Block faces sent to chosen B-rep faces; other outer faces go to the nearest surfaces.").hint(r#"[{"block": 0, "face": "+x", "to": ["F1:+x"]}]"#),
+    json("divisions", "Divisions").help("Element counts per block direction.").hint(r#"[{"block": 0, "direction": 1, "count": 8}]"#),
+    json("fixed", "Fixed faces")
+        .help("Faces of the body another body's mesh already covers: its element faces there are kept as they are and this mesh meets them node to node.")
+        .hint(r#"["F3:partition:P:b"]"#),
+    choice("smoothing", "Smoothing", &[("elliptic", "Elliptic"), ("elliptic-controlled", "Elliptic, controlled (Thomas–Middlecoff)"), ("laplace", "Laplace"), ("none", "None")])
+        .help("How interior nodes are smoothed after projection, with the boundary held on the geometry.")
+        .def("\"elliptic\""),
+    int("iterations", "Iterations", 1, 100_000).help("Smoothing iterations.").def("100"),
+    range("min_quality", "Minimum quality", D::None, 0.0, 1.0).help("Smallest scaled Jacobian accepted.").def("0.2"),
+    range("max_arc_angle", "Max arc angle", D::Degree, 0.0, 90.0)
+        .help("The most a curved face may turn across one element; the divisions grow to keep it. 0 for no limit.")
+        .def("30"),
+    range("merge", "Merge distance", D::Millimetre, 0.0, 1.0e9)
+        .help("Join this mesh's nodes with other bodies' meshes within this distance; 0 never.")
+        .hint("1e-6 of the diagonal"),
+    flag("preview", "Preview only").help("Return the block topology without meshing."),
+    TOLERANCE,
+];
+
+pub const CLEAR_MESH: &[Field] = &[references("bodies", "Bodies", C::Body)
+    .help("The bodies whose meshes go. When none is ticked: the meshes of bodies the open design no longer has because its partitions changed (model.check lists them).")
+    .hint("the bodies partitions removed")];
+
+const MIRROR_DATUM: Field = reference("", "Datum plane", C::DatumPlane).help("A datum plane of the model.");
+const MIRROR_POINT_NORMAL: &[Field] = &[
+    xyz("point", "Point", D::Length).help("A point on the plane.").req(),
+    xyz("normal", "Normal", D::None).help("The plane's normal; its length does not matter.").req(),
 ];

 pub const MIRROR: &[Field] = &[
-    json("plane", "Plane")
-        .help("The mirror plane: a datum plane's name, or a point and normal as JSON.")
-        .req()
-        .hint(r#""Datum" or {"point": [x, y, z], "normal": [nx, ny, nz]}"#),
+    name_or("plane", "Plane", &MIRROR_DATUM, "Point and normal", MIRROR_POINT_NORMAL)
+        .help("The mirror plane: a datum plane, or a point on it and its normal.")
+        .req(),
    references("bodies", "Bodies", C::Body).help("The meshed bodies to mirror; every meshed body when empty.").hint("every meshed body"),
-    json("as", "Images")
-        .help("Names for the mirrored bodies, as JSON.")
-        .hint(r#"{"body": "image body"}; default: the design's body at the reflected place"#),
+    reference_text("as", "Images", C::Body)
+        .help("The body each mirrored body becomes; when empty, the design's body at the reflected place, else <body>/mirror.")
+        .hint("default"),
 ];

 pub const SYMMETRY: &[Field] = &[
@@ -1100,6 +1255,37 @@ pub const HEX_OCTREE: &[Field] = &[
    FEATURE_ANGLE,
 ];

+/// A face by body and persistent name, a row of a face list.
+const FACE_ROW: &[Field] = &[
+    reference("body", "Body", C::Body).help("A body of the open design.").req(),
+    text("face", "Face").help("A persistent face name of the body (e.g. F3).").req().hint("persistent face name"),
+];
+const fn face_rows(key: &'static str, label: &'static str) -> Field {
+    rows(key, label, FACE_ROW)
+}
+
+pub const HEX_EXTRUDE: &[Field] = &[
+    face_rows("source", "Source")
+        .help("The section: faces already meshed (by this body or a neighbour, whose nodes are shared), or one planar face meshed here. Pick it, then Use as source.")
+        .hint("pick the source face"),
+    reference("source_set", "Source set", C::Set).help("Instead of Source: a set of quadrilaterals (a 2D mesh, or hex element faces)."),
+    face_rows("to_surface", "Target surface")
+        .help("The faces the last layer lies on. Pick them, then Use as target surface.")
+        .req()
+        .hint("pick the target surface"),
+    face_rows("sides", "Side faces").help("The faces the section's sides follow (they need not be straight); straight paths when empty.").hint("straight sides"),
+    xyz("direction", "Direction", D::None).help("The direction every node moves along; along the section's normal toward the target when empty.").hint("the section's normal"),
+    flag("normal", "Along the normal").help("Each node along the section's normal toward the target (the default when no direction is given)."),
+    int("layers", "Layers", 1, 10_000).help("The number of element layers; from Size when empty.").hint("from the size"),
+    positive("size", "Size", D::Length).help("Layer thickness, and the element size of a section meshed here.").hint("1/25 of the body"),
+    range("bias", "Bias", D::None, 0.001, 1000.0).help("The last layer's thickness over the first's: below 1 grades toward the target, above 1 toward the source.").def("1"),
+    reference("body", "Body", C::Body).help("The body the elements fill; its mesh is replaced.").hint("the source face's body"),
+    TOLERANCE,
+];
+
+/// A block's edge directions, from corner 1.
+const BLOCK_DIRECTIONS: &[&str] = &["1-2", "1-4", "1-5"];
+
 pub const BLOCK: &[Field] = &[
    text("body", "Body").help("Name of the new block body.").req().def("\"Block\""),
    choice(
@@ -1120,9 +1306,13 @@ pub const BLOCK: &[Field] = &[
    .help("The element type of the block.")
    .req()
    .def("\"hex8\""),
-    json("corners", "Corners").help("The eight corner points (four for 2D), as JSON.").req().hint("[[x, y, z] × 8] (2D: × 4 at z = 0)"),
-    json("divisions", "Divisions").help("Elements along each edge direction, as JSON.").req().hint("[n12, n14, n15] (2D: [n12, n14])"),
-    json("bias", "Bias").help("Element size ratio along each direction, as JSON; 1 is uniform.").hint("[1, 1, 1]"),
+    points("corners", "Corners", D::Length, 8).help("The eight corner points (four for 2D, at z = 0).").req(),
+    tuple("divisions", "Divisions", BLOCK_DIRECTIONS, 2, true)
+        .help("Elements along each edge direction: corner 1 to 2, 1 to 4 and 1 to 5; a 2D block takes the first two.")
+        .req(),
+    tuple("bias", "Bias", BLOCK_DIRECTIONS, 2, false)
+        .help("Last over first element size along each direction; 1 is uniform. A 2D block takes the first two.")
+        .hint("uniform"),
    json("edges", "Curved and named edges").help("Edge curves and names, as JSON."),
    json("faces", "Face names").help("Names of the block's faces, as JSON.").hint("{\"1\": \"bottom\"}"),
    json("vertices", "Corner names").help("Names of the block's corners, as JSON."),
@@ -1145,10 +1335,29 @@ pub const PLANAR: &[Field] = &[
 ];

 pub const QUALITY: &[Field] = &[
-    json("elements", "Elements").help("The elements to measure, as JSON labels; all when empty.").hint("[labels]; all when empty"),
+    labels("elements", "Elements", LabelOf::Element).help("The elements to measure; all when empty.").hint("all"),
    int("bins", "Histogram bins", 1, 1000).help("Number of bars in the quality histogram.").def("10"),
 ];

+pub const QUALITY_MARK: &[Field] = &[
+    labels("elements", "Elements", LabelOf::Element).help("The elements to check; all when empty.").hint("all"),
+    group(
+        "limits",
+        "Limits",
+        &[
+            num("scaled_jacobian", "Scaled Jacobian at least", D::None)
+                .help("Elements with a lower scaled Jacobian are marked (1 is a perfect element).")
+                .hint("0.2"),
+            num("min_dihedral", "Min dihedral at least", D::Degree).help("Tetrahedra with a smaller dihedral angle are marked.").hint("10"),
+            num("max_dihedral", "Max dihedral at most", D::Degree).help("Tetrahedra with a larger dihedral angle are marked.").hint("165"),
+            num("aspect_ratio", "Aspect ratio at most", D::None).help("Elements with a larger aspect ratio are marked.").hint("10"),
+            num("min_angle", "Min angle at least", D::Degree).help("Shells with a smaller corner angle are marked.").hint("15"),
+            num("max_angle", "Max angle at most", D::Degree).help("Shells with a larger corner angle are marked.").hint("165"),
+        ],
+    )
+    .help("Elements worse than a limit are marked; a limit left empty keeps its default."),
+];
+
 pub const SURFACE_CHECK: &[Field] = &[
    reference("body", "Body", C::Body).help("The body whose surface to check.").req().hint("or an imported surface"),
    SURFACE,
@@ -1178,6 +1387,7 @@ pub const ELEMENT_ADD: &[Field] = &[
            ("tet4", "tet4"),
            ("tet10", "tet10"),
            ("wedge6", "wedge6"),
+            ("pyramid5", "pyramid5"),
            ("hex8", "hex8"),
            ("hex20", "hex20"),
        ],
@@ -1185,7 +1395,61 @@ pub const ELEMENT_ADD: &[Field] = &[
    .help("The element type.")
    .req()
    .def("\"hex8\""),
-    json("nodes", "Nodes").help("The element's node labels in order, as JSON.").req().hint("[labels]"),
+    labels("nodes", "Nodes", LabelOf::Node).help("The element's node labels in order.").req().hint("labels in order: 1, 2, 3, 4"),
+];
+
+const MERGE_TOLERANCE: Field =
+    positive("tolerance", "Tolerance", D::Length).help("Nodes closer than this are one node.").hint("a millionth of the mesh's size");
+
+pub const NODE_MERGE: &[Field] = &[
+    MERGE_TOLERANCE,
+    reference("set", "Set", C::Set).help("Merge only the nodes of this set (and of its elements and faces).").hint("every node"),
+    choice("keep", "Keep", &[("lowest", "Lowest label"), ("highest", "Highest label")]).help("Which node of each group survives.").def("\"lowest\""),
+];
+
+pub const CHECK_DUPLICATES: &[Field] = &[MERGE_TOLERANCE];
+
+pub const NODE_RELAX: &[Field] = &[
+    xyz("center", "Centre", D::Length).help("The centre of the sphere of influence; click the mesh to place it.").hint("click the mesh"),
+    positive("radius", "Radius", D::Length).help("Nodes closer to the centre than this move; Alt + scroll over the view changes it."),
+    int("around_element", "Around element", 1, 99_999_999)
+        .help("Instead of a centre: a sphere round this element (radius default twice its longest edge).")
+        .hint("none"),
+    face_rows("faces", "Faces")
+        .help("Instead of a sphere: every node on these CAD faces and the elements touching them, nodes sliding on the faces. Shift-click faces in the view, then Use selection.")
+        .hint("Shift-click faces"),
+    labels("nodes", "Nodes", LabelOf::Node).help("Instead of a sphere: these nodes.").hint("none"),
+    labels("elements", "Elements", LabelOf::Element).help("Instead of a sphere: the nodes of these elements.").hint("none"),
+    references("bodies", "Bodies", C::Body).help("Only the nodes of these bodies.").hint("every body"),
+    choice("mode", "Mode", &[("guarded", "Guarded (local)"), ("strong", "Strong (optimise the region)")])
+        .help("Guarded: each move keeps the worst element around the node from getting worse. Strong: move the nodes of the bad elements and morph the mesh round them, nodes on CAD edges held.")
+        .def("\"guarded\""),
+    range("below", "Below", D::None, 0.0, 1.0).help("Strong: the elements below this scaled Jacobian are moved.").hint("0.7"),
+    positive("reach", "Reach", D::Length).help("Strong: nodes this close to a moved node follow it, blended to zero at the reach.").hint("three element lengths"),
+    int("iterations", "Iterations", 1, 200).help("Guarded: sweeps over the nodes (1 to 100). Strong: morph rounds.").hint("5 (strong: 20)"),
+    range("strength", "Strength", D::None, 0.0, 1.0).help("How far each node moves toward its relaxed position, 0 to 1.").def("1"),
+    choice("falloff", "Falloff", &[("smooth", "Smooth"), ("linear", "Linear"), ("none", "None")])
+        .help("How the strength falls from the centre to the radius, so the edit blends into the mesh.")
+        .def("\"smooth\""),
+    text("field", "Keep as").help("The relaxation field to keep, to apply again after a remesh.").hint("Relax1, Relax2, …"),
+    flag("reapply", "Reapply after remesh").help("Apply the field again by itself after each remesh.").def("false"),
+];
+
+pub const NODE_RELAX_APPLY: &[Field] = &[
+    text("field", "Field").req().help("The relaxation field kept by Relax Nodes."),
+    references("bodies", "Bodies", C::Body).help("Only the nodes of these bodies.").hint("the field's bodies"),
+    range("polish", "Polish", D::None, 0.0, 1.0).help("Strength of one guarded smoothing sweep after the field is applied; 0 for none.").def("0.3"),
+];
+
+pub const RENUMBER: &[Field] = &[
+    choice("what", "Renumber", &[("both", "Nodes and elements"), ("nodes", "Nodes"), ("elements", "Elements")])
+        .help("Which labels change.")
+        .def("\"both\""),
+    choice("by", "Order", &[("compact", "Compact (label order)"), ("bandwidth", "Bandwidth (reverse Cuthill–McKee)"), ("body", "Body by body")])
+        .help("The order of the new labels.")
+        .def("\"compact\""),
+    int("start", "Start", 1, 99_999_999).help("The first new label.").def("1"),
+    int("offset", "Offset", -99_999_999, 99_999_999).help("Instead of an order and a start: add this to every label.").hint("none"),
 ];

 pub const SEED_EDGE: &[Field] = &[
@@ -1214,7 +1478,7 @@ pub const SEED_EDGE: &[Field] = &[

 pub const SEED_CLEAR: &[Field] = &[json("edges", "Edges").help("The edges to clear, as JSON; every seed when empty.").hint("every seed")];

-pub const DELAUNAY_POINTS: &[Field] = &[json("points", "Points").help("The points to triangulate, as JSON.").req().hint("[[x, y, z], …]")];
+pub const DELAUNAY_POINTS: &[Field] = &[points("points", "Points", D::Length, 20_000).help("The points to triangulate.").req()];

 pub const TAG: &[Field] = &[
    group(
@@ -1229,10 +1493,10 @@ pub const TAG: &[Field] = &[
    )
    .help("The geometry the mesh entities are tagged with.")
    .req(),
-    json("elements", "Elements").help("Element labels, as JSON."),
-    json("faces", "Element faces").help("Element faces, as JSON."),
-    json("edges", "Element edges").help("Element edges, as JSON."),
-    json("nodes", "Nodes").help("Node labels, as JSON."),
+    labels("elements", "Elements", LabelOf::Element).help("Element labels."),
+    sides("faces", "Element faces", Side::Face).help("Element faces as element:face: 1-20:3, 25:1.").hint("element:face"),
+    sides("edges", "Element edges", Side::Edge).help("Element edges as element:edge: 1-20:3, 25:1.").hint("element:edge"),
+    labels("nodes", "Nodes", LabelOf::Node).help("Node labels."),
 ];

 // ---- Geometry and files ----
@@ -1346,6 +1610,33 @@ pub const DATUM_AXIS: &[Field] = &[
    .req()
    .def(r#"{"type": "principal"}"#),
 ];
+pub const RIGID_WALL: &[Field] = &[
+    reference("step", "Step", C::Step)
+        .help("The explicit dynamics step the wall acts in; the model's only one when empty.")
+        .hint("the explicit step"),
+    reference("set", "Set", C::Set).help("The nodes the wall stops: pick them and Use selection.").req(),
+    xyz("point", "Point", D::Length).help("A point on the wall.").req().def("[0, 0, 0]"),
+    xyz("normal", "Normal", D::None).help("The wall's normal, pointing to the side the nodes stay on.").req().def("[0, 0, 1]"),
+    FRICTION,
+];
+pub const RIGID_WALL_DELETE: &[Field] = &[
+    reference("step", "Step", C::Step).help("The explicit dynamics step.").req(),
+    int("index", "Wall", 0, MAX_ROWS as i64).help("The wall's place in the step's rigid walls, from 0.").req(),
+];
+pub const CENTRE: &[Field] = &[
+    rows(
+        "geometry",
+        "Geometry",
+        &[
+            reference("body", "Body", C::Body).help("A body of the open design.").req(),
+            text("face", "Face").help("A persistent face name of the body."),
+            text("edge", "Edge").help("A persistent edge name of the body."),
+            text("vertex", "Vertex").help("A persistent vertex name of the body."),
+        ],
+    )
+    .help("Faces or edges (a hole's faces or rim give its centre), or one vertex."),
+    labels("nodes", "Nodes", LabelOf::Node).help("Mesh node labels: their mean.").hint("labels: 1, 2, 10-20"),
+];
 pub const DATUM_POINT: &[Field] = &[
    NAME,
    variants(
@@ -1355,10 +1646,12 @@ pub const DATUM_POINT: &[Field] = &[
            variant("coordinates", "Coordinates", &[xyz("point", "Point", POINT).help("The point's coordinates.").req()]),
            variant(
                "vertex",
-                "Mesh vertex",
+                "Vertex",
                &[
                    reference("body", "Body", C::Body).help("The body the vertex belongs to.").req(),
-                    text("vertex", "Vertex").help("The vertex's name, as the mesh tags it.").req(),
+                    text("vertex", "Vertex")
+                        .help("The vertex's persistent name: pick it with Select: Vertices and Use selection (geometry.bodies lists every body's vertices).")
+                        .req(),
                ],
            ),
            variant(
@@ -1426,6 +1719,64 @@ pub const PARTITION: &[Field] = &[
    references("bodies", "Bodies", C::Body).help("The bodies to divide; every body the plane cuts when empty.").hint("every body the plane divides"),
 ];
 pub const PARTITION_DELETE: &[Field] = existing!("Partition", C::Partition);
+pub const FACES_MERGE: &[Field] = &[
+    NAME,
+    face_rows("faces", "Faces")
+        .help("Two or more adjacent faces of one body, meshed as one face. Shift-click faces in the view, then Use selection.")
+        .req()
+        .hint("Shift-click faces"),
+];
+pub const FACE_ABSORB: &[Field] = &[
+    text("name", "Name").help("The absorption's name (with From check: the prefix of each one's, Name-1, Name-2, …).").hint("Absorb"),
+    group("face", "Face", FACE_ROW).help("The tiny or sliver face to absorb; leave empty with From check."),
+    text("into", "Into").help("The neighbour face that absorbs it, by persistent name.").hint("the neighbour sharing the longest edges"),
+    flag("from_check", "From check").help("Absorb every small and sliver face the last Check Geometry found, each into its best neighbour."),
+];
+pub const STITCH: &[Field] = &[
+    NAME,
+    text("surface", "Surface").help("The imported surface to stitch, by name.").req(),
+    positive("tolerance", "Tolerance", D::Length)
+        .help("Gaps narrower than this close: open points this close become one, and a point this close to another open edge splits it.")
+        .req(),
+];
+pub const STITCH_DELETE: &[Field] = existing!("Stitch", C::Stitch);
+pub const FACE_SPLIT: &[Field] = &[
+    NAME,
+    group("face", "Face", FACE_ROW).help("The face to split.").req(),
+    reference("datum", "Datum plane", C::DatumPlane).help("The plane the face is split along.").req(),
+];
+pub const FACE_SPLIT_DELETE: &[Field] = existing!("Face split", C::FaceSplit);
+pub const FACES_MERGE_DELETE: &[Field] = existing!("Face merge", C::FaceMerge);
+pub const MESH_PLAN: &[Field] = &[
+    reference("body", "Body", C::Body).help("The body of the design to plan (as opened, not a partition cell).").req(),
+    text("name", "Name").help("The name the plan is saved under.").hint("Plan-<body>"),
+    positive("size", "Element size", D::Millimetre).help("The largest element size; thin walls make it smaller.").hint("1/25 of the diagonal"),
+    int("layers", "Layers through walls", 1, 10).help("Elements through the thinnest wall the features give (a shell, a plate).").hint("2"),
+    int("max_elements", "Most elements", 1, 5_000_000).help("The size grows past the walls' when more elements would be needed.").hint("300000"),
+];
+pub const MESH_PLAN_APPLY: &[Field] = &[
+    text("plan", "Plan").help("The name of a saved mesh plan (mesh.plan).").req(),
+    flag("symmetry", "Use symmetry")
+        .help("Mesh one cell of a body that is its own mirror image across planes through its middle, and mirror it.")
+        .def("true"),
+    flag("corners", "Copy corners")
+        .help("With symmetry: when the body's two ends along another axis are alike (an enclosure's corners), mesh one end and mirror it onto the other, the middle meshed to fit both.")
+        .def("true"),
+    text("name", "Save as").help("The name a plan given as an object is saved under.").hint("Plan-<body>"),
+];
+pub const FEATURES: &[Field] = &[reference("body", "Body", C::Body).help("Only this body's features.").hint("every body")];
+pub const GEOMETRY_CHECK: &[Field] = &[
+    reference("body", "Body", C::Body).help("The body to check; every body when empty.").hint("every body"),
+    positive("size", "Element size", D::Millimetre)
+        .help("The element size you intend to mesh with; features are small against it.")
+        .hint("1/20 of the diagonal"),
+    range("short_edge", "Short edge", D::None, 0.0, 10.0).help("Edges shorter than this fraction of the size are reported.").def("0.3"),
+    range("small_face", "Small face", D::None, 0.0, 10.0).help("Faces with area below this fraction of size² are reported.").def("0.1"),
+    range("sliver", "Sliver width", D::None, 0.0, 10.0).help("Faces narrower than this fraction of the size are reported.").def("0.3"),
+    range("gap", "Gap", D::None, 0.0, 10.0).help("Parallel faces closer than this fraction of the size, but not touching, are reported.").def("0.3"),
+    range("parallel_angle", "Parallel within", D::Degree, 0.0, 60.0).help("Faces this close to parallel count for the gap.").def("10"),
+    flag("mark", "Mark findings").help("Mark what is found in the viewport until the design changes.").def("true"),
+];
 pub const TESSELLATE: &[Field] = &[reference("body", "Body", C::Body).help("The body to tessellate.").req(), TOLERANCE];
 pub const IMPORT_MESH: &[Field] = &[path("path", "3MF file", false).help("A 3MF surface mesh with named faces.").req()];
 pub const FILE_OPEN: &[Field] = &[path("path", "Model", false).help("The FieldCraft model file to open.").req()];
@@ -1441,6 +1792,11 @@ pub const CRASH_REPORT: &[Field] = &[
    text("id", "Report").help("The crash report to show.").req(),
    path("dir", "Folder", false).help("The crash folder; the default one when empty.").hint("the crash folder"),
 ];
+pub const CRASH_REPORTS_DELETE: &[Field] = &[
+    text("id", "Report").help("The crash report to delete.").hint("or All"),
+    flag("all", "All").help("Delete every crash report instead of one."),
+    path("dir", "Folder", false).help("The crash folder; the default one when empty.").hint("the crash folder"),
+];
 pub const BUG_REPORT: &[Field] = &[
    text("title", "Title").help("The issue's title; one is made up when empty."),
    text("observed", "What happened").help("What went wrong; the last error when empty."),
@@ -1466,6 +1822,7 @@ pub const SAMPLE: &[Field] = &[choice(
        ("cantilever", "Cantilever"),
        ("impact", "Impact"),
        ("parts", "Parts"),
+        ("ibeam", "I-beam cantilever"),
        ("drop-test", "Drop test"),
        ("rubber-seal", "Rubber seal"),
        ("flow-past", "Flow past a bracket"),
@@ -1489,13 +1846,20 @@ pub const DECK: &[Field] = &[
    references("steps", "Steps", C::Step).help("The steps to write; all when empty.").hint("all"),
 ];

+pub const EXPORT_STL: &[Field] = &[
+    path("path", "File", true).help("Where to write the STL file.").req(),
+    reference("set", "Set", C::Set).help("Write only this set's element faces; the whole outer surface when empty.").hint("the outer surface"),
+    choice("format", "Format", &[("binary", "Binary"), ("ascii", "ASCII")]).help("Binary is compact; ASCII is readable text.").def("\"binary\""),
+];
+
 // ---- Solving ----

 const STEP: Field = reference("step", "Step", C::Step).help("The step to solve; the only one when empty.").hint("the only one");
 const SOLVED: Field = reference("step", "Step", C::SolvedStep).help("The solved step; the step shown when empty.").hint("the step shown");
 const MAX_DOFS: Field = int("max_dofs", "Max DOFs", 1, 6_000_000).help("Cap on the degrees of freedom solved.").hint("6000000");
-const MAX_FACTOR: Field =
-    int("max_factor_entries", "Max factor entries", 1, 400_000_000).help("Cap on the factorised matrix size, which bounds memory.").hint("400000000");
+const MAX_FACTOR: Field = int("max_factor_entries", "Max factor entries", 1, super::solve::FACTOR_ENTRY_CEILING as i64)
+    .help("Cap on factor entries (8 bytes each): 400M by default; raise deliberately up to 2B (16 GB of values alone). Indices, workspace and other solver storage need additional memory.")
+    .hint("400000000");
 const THREADS: Field = int("threads", "Threads", 1, 256).help("Threads to use; the session's setting when empty.").hint("the session's");

 pub const SOLVE_STATIC: &[Field] = &[STEP, MAX_DOFS, MAX_FACTOR, THREADS];
@@ -1538,13 +1902,13 @@ pub const SOLVE_FLUID: &[Field] = &[
 ];
 pub const SOLVE_PROBE: &[Field] = &[
    SOLVED.req(),
-    json("nodes", "Nodes").help("Node labels to read, as JSON.").hint("[labels]"),
+    labels("nodes", "Nodes", LabelOf::Node).help("Node labels to read.").hint("labels: 1, 2, 10-20"),
    reference("set", "Set", C::Set).help("A set whose nodes to read."),
-    json("at", "Points").help("Points to read at the nearest nodes, as JSON.").hint("[[x, y, z], …]: nearest nodes"),
+    points("at", "Points", D::Length, 10_000).help("Points to read at the nearest nodes."),
    int("mode", "Mode", 1, 1_000_000).help("The mode to read, for frequency and buckling steps."),
    int("frame", "Frame", 0, 1_000_000_000).help("The frame to read, for explicit and transient steps."),
    flag("elements", "Element results").help("Also read element results (stresses) around the nodes."),
-    json("points", "Fluid points").help("Points in the fluid to read, as JSON.").hint("[[x, y, z], …]"),
+    points("points", "Fluid points", D::Length, 10_000).help("Points in the fluid to read."),
    json("forces", "Fluid walls").help("Walls whose fluid forces to sum, as JSON.").hint("[\"x_min\", \"F2:top\"]"),
 ];

@@ -1553,7 +1917,7 @@ pub const SOLVE_PROBE: &[Field] = &[
 pub const DEFORMED: &[Field] = &[
    SOLVED,
    flag("show", "Show").help("Show the deformed shape.").def("true"),
-    json("scale", "Scale").help("Displacement magnification: auto, or a factor (1 is true scale).").def("\"auto\"").hint("\"auto\" or a factor"),
+    number_or_auto("scale", "Scale", D::None, Some(0.0)).help("Displacement magnification: auto, or a factor (1 is true scale).").def("\"auto\""),
 ];
 pub const CONTOUR: &[Field] = &[
    SOLVED,
@@ -1587,6 +1951,15 @@ pub const CONTOUR: &[Field] = &[
    .req()
    .def("\"von_mises\""),
    int("bands", "Bands", 2, 24).help("Number of colour bands.").def("12"),
+    group(
+        "range",
+        "Legend range",
+        &[
+            num("min", "Min", D::None).help("Values below it take the lowest colour.").hint("the field's minimum"),
+            num("max", "Max", D::None).help("Values above it are drawn in the over colour.").hint("the field's maximum"),
+        ],
+    )
+    .help("Clamp the legend, e.g. below a singular peak; empty follows the field."),
 ];
 pub const MODES: &[Field] = &[SOLVED, int("mode", "Mode", 1, 1_000_000).help("The mode shape shown.").def("1")];
 pub const ANIMATE: &[Field] = &[flag("on", "Animate").help("Play the deformation or the frames.").def("true")];
@@ -1595,6 +1968,41 @@ pub const FRAME: &[Field] = &[
    int("frame", "Frame", 0, 1_000_000_000).help("The frame shown."),
    positive("time", "Time", D::Time).help("Show the frame nearest this time; the last when empty.").hint("the last frame"),
 ];
+pub const EXPORT_CSV: &[Field] = &[
+    choice("what", "Export", &[("reactions", "Reaction sums"), ("probe", "Probed nodes")]).help("What to write.").req().def("\"reactions\""),
+    path("path", "File", true).help("The CSV file to write.").req(),
+    SOLVED,
+    references("sets", "Sets", C::Set).help("Reactions: the sets to sum; the step's BC sets when empty.").hint("the step's BC sets"),
+    xyz("about", "About point", D::Length).help("Reactions: the point moments are taken about."),
+    labels("nodes", "Nodes", LabelOf::Node).help("Probe: the node labels."),
+    reference("set", "Set", C::Set).help("Probe: a set whose nodes to read."),
+    points("at", "Points", D::Length, 10_000).help("Probe: points to read at the nearest nodes."),
+    int("mode", "Mode", 1, 1_000_000).help("Probe: the mode to read, for frequency and buckling steps."),
+    int("frame", "Frame", 0, 1_000_000_000).help("Probe: the frame to read, for explicit and transient steps."),
+];
+pub const RESULTS_XY: &[Field] = &[
+    SOLVED,
+    json("y", "Quantity")
+        .help("What to plot: a nodal field at a node, an explicit energy or history, a history node's quantity, or \"frequency\".")
+        .hint(r#"{"field": "displacement_z", "node": 21}"#)
+        .req(),
+    choice("x", "Against", &[("auto", "The step's own axis"), ("load_factor", "Load factor"), ("time", "Time"), ("mode", "Mode")])
+        .help("The x axis: the load factor (nonlinear static), time (explicit, heat) or mode number (frequency).")
+        .def("\"auto\""),
+    int("every", "Keep one in", 1, 1_000_000_000).help("Keep one point in this many; by default enough to fit 100000 points."),
+    path("path", "CSV file", true).help("Also write the series as a two-column CSV."),
+];
+pub const EXPORT_VTU: &[Field] = &[
+    path("path", "File", true).help("A .vtu file for one state, or a .pvd collection for every frame or mode.").req(),
+    SOLVED,
+    int("mode", "Mode", 1, 1_000_000).help("Frequency steps: the mode to write; every mode in a .pvd when empty.").hint("all (.pvd) or 1"),
+    choice("frames", "Frames", &[("all", "Every frame"), ("last", "The last frame")])
+        .help("A .pvd series: every frame or only the last.")
+        .def("\"all\""),
+    choice("encoding", "Encoding", &[("ascii", "Text"), ("binary", "Binary (base64)")])
+        .help("Text is readable; binary is smaller and exact.")
+        .def("\"ascii\""),
+];
 pub const REACTIONS: &[Field] = &[
    SOLVED,
    references("sets", "Sets", C::Set)
@@ -1720,9 +2128,11 @@ mod tests {
        "`boundary_conditions` or `loads`",
        "give one of",
        "is not an explicit",
+        "has no explicit dynamics step",
        "has a result",
        "no crash report",
        "FIELDCRAFT_CRASH_TEST",
+        "no relaxation field",
    ];

    /// Fill top-level required names (a fresh one) and references (the first existing item).
@@ -1764,6 +2174,10 @@ mod tests {
                }
                match f.kind {
                    Kind::Group(g) | Kind::Rows { fields: g, .. } | Kind::Either(g) => walk(id, g, missing),
+                    Kind::NameOr { name, fields, .. } => {
+                        walk(id, std::slice::from_ref(name), missing);
+                        walk(id, fields, missing);
+                    }
                    Kind::Variants { variants, .. } => variants.iter().for_each(|v| walk(id, v.fields, missing)),
                    _ => {}
                }
@@ -16,7 +16,7 @@ use crate::{CommandKind, CommandSpec, EngineError, Result, Session};
 pub const OPEN: CommandSpec = CommandSpec {
    id: "geometry.open",
    label: "Open Design",
-    params: r#"{"path": "part.solidcraft", "model"?: "keep"} — rebuilds the SolidCraft design and makes its bodies the geometry. `model`: "keep" (default) keeps the mesh and every definition, so opening the same design again after an edit picks up the change and sets follow their persistent face names; "new" starts a new model with the design (no mesh, sets, materials, sections, BCs, loads or steps; the unit system stays; the model is untitled until saved, and undo restores the previous file). The reply's `related` is false when the model (before the open) refers to bodies (mesh tags, set geometry) and the design has none of them, and `stale` lists what no longer resolves: `mesh_bodies` (bodies the mesh is tagged with that the design lacks) `sets` (sets naming a body or face it lacks) and `seeds` (edge seeds on edges it lacks). One undo step"#,
+    params: r#"{"path": "part.solidcraft", "model"?: "keep"} — rebuilds the SolidCraft design and makes its bodies the geometry. `model`: "keep" (default) keeps the mesh and every definition, so opening the same design again after an edit picks up the change and sets follow their persistent face names; "new" starts a new model with the design (no mesh, sets, materials, sections, BCs, loads or steps; the unit system stays; the model is untitled until saved, and undo restores the previous file). The reply's `related` is false when the model (before the open) refers to bodies (mesh tags, set geometry) and the design has none of them, and `stale` lists what no longer resolves: `mesh_bodies` (bodies the mesh is tagged with that the design lacks) `sets` (sets naming a body or face it lacks) and `seeds` (edge seeds on edges it lacks). `errors` lists the features that failed to rebuild with the `bodies` each may change, and `warnings` says so in one line each. One undo step"#,
    form: Some(super::forms::OPEN_DESIGN),
    kind: CommandKind::Model,
    requires: &[],
@@ -26,13 +26,43 @@ pub const OPEN: CommandSpec = CommandSpec {
 pub const BODIES: CommandSpec = CommandSpec {
    id: "geometry.bodies",
    label: "Bodies",
-    params: "{} — the open design's bodies: measures, persistent face names (by face index) and edges (persistent name `<face>|<face>`, `~k` when several separate the same faces, and length)",
+    params: "{} — the open design's bodies: measures, persistent face names (by face index) and edges (persistent name `<face>|<face>`, `~k` when several separate the same faces, and length) and vertices (persistent name `<face>|<face>|<face>` after the faces that meet there, `~k` when several touch the same faces, and point)",
    form: Some(&[]),
    kind: CommandKind::Model,
    requires: &[], // No design is an answer too: no bodies.
    run: bodies,
 };

+pub const FEATURES: CommandSpec = CommandSpec {
+    id: "geometry.features",
+    label: "Feature Graph",
+    params: r#"{"body"?: "Base" (default: every body)} — the features of the SolidCraft timeline that built each body of the open design, in order (read-only): each feature's `id` (`F<id>` in persistent names), `name`, `type` (extrude, box, cylinder, hole, shell, fillet, combine, pattern, mirror, split, …), `operation` (new_body, join, cut, intersect), `values` (its numeric inputs evaluated: mm, radians, counts), `placement` (a primitive's corner, base or centre), `direction` (an extrude's along the sketch normal, a cylinder's axis, a hole's drilling direction), `two_sided`, `sketch` (plane origin, axes and normal, and the profiles used: lines, arcs and circles in sketch coordinates, holes, curve ids), `transforms` (pattern and mirror copies, 4×4 row-major), `targets` and `tools`, the stored `definition`, the persistent `faces` and `edges` of the body it made, and `error` when it failed to rebuild. A partition cell is described by the body it was cut from"#,
+    form: Some(super::forms::FEATURES),
+    kind: CommandKind::Model,
+    requires: &[Requirement::Design],
+    run: features,
+};
+
+pub const CENTRE: CommandSpec = CommandSpec {
+    id: "geometry.centre",
+    label: "Centre of Selection",
+    params: r#"{"geometry": [{"body": "Body1", "face": "F3:hole"} | {"body", "edge"} | {"body", "vertex"}], "nodes": [labels]} — the point a reference point or datum point goes at for what is picked: a vertex's point; the mean of nodes; the centre of a hole (cylindrical faces on one axis, or circular edges on one circle: the axis point at their mid-depth, the circle's centre); otherwise the area centroid of the faces and the length centroid of the edges. Replies `point` and `from` (`vertex`, `nodes`, `circle`, `centroid`)"#,
+    form: Some(super::forms::CENTRE),
+    kind: CommandKind::Model,
+    requires: &[],
+    run: centre,
+};
+
+pub const CHECK: CommandSpec = CommandSpec {
+    id: "geometry.check",
+    label: "Check Geometry",
+    params: r#"{"body"?: "Body1" (default: every body of the open design), "size"?: mm (the target element size; default a twentieth of the smallest checked body's bounding-box diagonal), "short_edge": 0.3, "small_face": 0.1, "sliver": 0.3, "gap": 0.3 (fractions of the size, 0..=10), "parallel_angle": 10 (degrees, 0..=60)} — before meshing, finds what is small against the size (read-only): `short_edge` edges shorter than short_edge × size, `small_face` faces with area below small_face × size², `sliver_face` faces narrower (2 × area / perimeter) than sliver × size, and `near_faces` pairs of faces within parallel_angle of parallel that are closer than gap × size without touching (a gap between bodies or cells, an overlap, or a wall thinner than the gap; faces within twice the tessellation tolerance touch). Replies `size`, `counts` per kind, `summary`, and `findings` (by kind, worst first, at most 1000; `truncated` says when more were found), each with `kind`, `body`, `edge`, `faces` (persistent names; near faces: the second on `other_body`), `value` (mm, mm²), `limit` and `at` (a point on it). `mark` (default true): the viewport and pictures mark the findings in the marker colour (their faces, short edges as lines, and a dot at each `at`) until the design changes or a check with `mark: false` or nothing found"#,
+    form: Some(super::forms::GEOMETRY_CHECK),
+    kind: CommandKind::Model,
+    requires: &[Requirement::Design],
+    run: check,
+};
+
 pub const TESSELLATE: CommandSpec = CommandSpec {
    id: "geometry.tessellate",
    label: "Tessellate Body",
@@ -86,7 +116,9 @@ fn open(s: &mut Session, p: &Value) -> Result<Value> {
    let out = json!({
        "name": design.name,
        "bodies": design.bodies.iter().map(|b| b.name.as_str()).collect::<Vec<_>>(),
-        "errors": design.errors.iter().map(|e| json!({"feature": e.feature, "message": e.message})).collect::<Vec<_>>(),
+        "errors": design.errors.iter().map(|e| json!({"feature": e.feature, "message": e.message, "bodies": e.bodies})).collect::<Vec<_>>(),
+        // Shown with the open: a body that differs from the design is never silent.
+        "warnings": design.errors.iter().map(|e| e.warning()).collect::<Vec<_>>(),
        "model": if new_model { "new" } else { "kept" },
        "related": fit.related,
        "stale": {"mesh_bodies": fit.mesh_bodies, "sets": fit.sets, "seeds": fit.seeds},
@@ -143,6 +175,7 @@ fn bodies(s: &mut Session, _: &Value) -> Result<Value> {
    for b in &design.bodies {
        let m = b.measure()?;
        let edges: Vec<Value> = b.edges()?.iter().map(|e| json!({"name": e.name, "length": e.length()})).collect();
+        let vertices: Vec<Value> = b.vertices()?.iter().map(|v| json!({"name": v.name, "point": v.point})).collect();
        out.push(json!({
            "name": b.name,
            "volume": m.volume,
@@ -151,11 +184,203 @@ fn bodies(s: &mut Session, _: &Value) -> Result<Value> {
            "bbox": [m.bbox_min, m.bbox_max],
            "faces": b.faces().iter().map(|f| json!({"name": f.name, "exact": f.exact})).collect::<Vec<_>>(),
            "edges": edges,
+            "vertices": vertices,
        }));
    }
    Ok(Value::Array(out))
 }

+fn features(s: &mut Session, p: &Value) -> Result<Value> {
+    let body = match p.get("body") {
+        None | Some(Value::Null) => None,
+        Some(v) => Some(v.as_str().ok_or_else(|| EngineError::param("body", ProblemKind::NotAName))?),
+    };
+    let design = s.design.as_deref().ok_or_else(|| EngineError::Params("open a design first".into()))?;
+    let graph = design.features(body)?;
+    Ok(json!({"bodies": graph}))
+}
+
+/// Most geometry items and nodes `geometry.centre` takes.
+const MAX_CENTRE_ITEMS: usize = 10_000;
+
+fn add3(a: [f64; 3], b: [f64; 3]) -> [f64; 3] {
+    [a[0] + b[0], a[1] + b[1], a[2] + b[2]]
+}
+
+fn sub3(a: [f64; 3], b: [f64; 3]) -> [f64; 3] {
+    [a[0] - b[0], a[1] - b[1], a[2] - b[2]]
+}
+
+fn scale3(a: [f64; 3], k: f64) -> [f64; 3] {
+    a.map(|v| v * k)
+}
+
+fn dot3(a: [f64; 3], b: [f64; 3]) -> f64 {
+    a[0] * b[0] + a[1] * b[1] + a[2] * b[2]
+}
+
+fn cross3(a: [f64; 3], b: [f64; 3]) -> [f64; 3] {
+    [a[1] * b[2] - a[2] * b[1], a[2] * b[0] - a[0] * b[2], a[0] * b[1] - a[1] * b[0]]
+}
+
+/// The centre of the circle through three points, `None` when they lie on a line.
+fn circumcentre(a: [f64; 3], b: [f64; 3], c: [f64; 3]) -> Option<[f64; 3]> {
+    let (u, v) = (sub3(b, a), sub3(c, a));
+    let n = cross3(u, v);
+    let nn = dot3(n, n);
+    if !(nn > 1e-24 * dot3(u, u) * dot3(v, v)) {
+        return None;
+    }
+    let k = add3(scale3(cross3(n, u), dot3(v, v)), scale3(cross3(v, n), dot3(u, u)));
+    Some(add3(a, scale3(k, 0.5 / nn)))
+}
+
+/// The centre of an edge's polyline when it is an arc or circle (every point at one distance
+/// from it, within a thousandth), else `None`.
+fn circle_centre(points: &[[f64; 3]]) -> Option<[f64; 3]> {
+    let n = points.len();
+    if n < 3 {
+        return None;
+    }
+    let closed = points.first().zip(points.last()).is_some_and(|(a, b)| dot3(sub3(*a, *b), sub3(*a, *b)) < 1e-18);
+    let pick = |f: f64| points.get(((n - 1) as f64 * f).round() as usize).copied();
+    let (a, b, c) = if closed { (pick(0.0)?, pick(1.0 / 3.0)?, pick(2.0 / 3.0)?) } else { (pick(0.0)?, pick(0.5)?, pick(1.0)?) };
+    let centre = circumcentre(a, b, c)?;
+    let r = dot3(sub3(a, centre), sub3(a, centre)).sqrt();
+    let on = points.iter().all(|p| (dot3(sub3(*p, centre), sub3(*p, centre)).sqrt() - r).abs() <= 1e-3 * r);
+    on.then_some(centre)
+}
+
+/// The length-weighted centre of a polyline and its length.
+fn polyline_centroid(points: &[[f64; 3]]) -> ([f64; 3], f64) {
+    let (mut sum, mut length) = ([0.0; 3], 0.0);
+    for w in points.windows(2) {
+        let l = dot3(sub3(w[1], w[0]), sub3(w[1], w[0])).sqrt();
+        sum = add3(sum, scale3(add3(w[0], w[1]), 0.5 * l));
+        length += l;
+    }
+    (if length > 0.0 { scale3(sum, 1.0 / length) } else { points.first().copied().unwrap_or_default() }, length)
+}
+
+fn centre(s: &mut Session, p: &Value) -> Result<Value> {
+    let geometry: Vec<GeometryRef> = super::opt(p, "geometry")?.unwrap_or_default();
+    let nodes: Vec<u32> = super::opt(p, "nodes")?.unwrap_or_default();
+    if geometry.len() + nodes.len() > MAX_CENTRE_ITEMS {
+        return Err(EngineError::Params(format!("geometry.centre takes at most {MAX_CENTRE_ITEMS} items")));
+    }
+    if geometry.is_empty() && nodes.is_empty() {
+        return Err(EngineError::Params("give one of `geometry` or `nodes`: what to find the centre of".into()));
+    }
+    if !geometry.is_empty() && !nodes.is_empty() {
+        return Err(EngineError::Params("give either `geometry` or `nodes`, not both".into()));
+    }
+    if !nodes.is_empty() {
+        let mut sum = [0.0; 3];
+        for n in &nodes {
+            let node = s.model.node(*n).ok_or_else(|| EngineError::Params(format!("no node {n}")))?;
+            sum = add3(sum, node.xyz);
+        }
+        return Ok(json!({"point": scale3(sum, 1.0 / nodes.len() as f64), "from": "nodes"}));
+    }
+    let design = s.design.as_deref().ok_or_else(|| EngineError::Params("open a design first".into()))?;
+    let shape = |b: &str| design.body(b).ok_or_else(|| EngineError::Params(format!("the design has no body `{b}`")));
+    if let [g] = geometry.as_slice()
+        && let Entity::Vertex(v) = &g.entity
+    {
+        let vertex = shape(&g.body)?.vertices()?.into_iter().find(|x| &x.name == v);
+        let vertex = vertex.ok_or_else(|| EngineError::Params(format!("body `{}` has no vertex `{v}`", g.body)))?;
+        return Ok(json!({"point": vertex.point, "from": "vertex"}));
+    }
+    // Hole centres: every face a cylinder about one axis, or every edge an arc of one circle.
+    let mut circles: Vec<[f64; 3]> = Vec::new();
+    let mut axis: Option<([f64; 3], [f64; 3])> = None;
+    let mut round = true;
+    // Centroids, weighted by area (faces) or length (edges).
+    let (mut faces_sum, mut faces_area, mut edges_sum, mut edges_length) = ([0.0; 3], 0.0, [0.0; 3], 0.0);
+    for g in &geometry {
+        let body = shape(&g.body)?;
+        match &g.entity {
+            Entity::Face(f) => {
+                let i = body.face_index(f).ok_or_else(|| EngineError::Params(format!("body `{}` has no face `{f}`", g.body)))?;
+                let c = body.face_centre(f)?;
+                let mesh = body.tessellate((body.size()? * fieldcraft_geometry::EDGE_TOLERANCE).max(1e-4))?;
+                let area: f64 = mesh
+                    .triangles
+                    .iter()
+                    .zip(&mesh.tri_face)
+                    .filter(|(_, t)| **t == i)
+                    .filter_map(|(t, _)| {
+                        let q = |k: usize| mesh.positions.get(t[k] as usize).copied();
+                        let (a, b, c) = (q(0)?, q(1)?, q(2)?);
+                        let n = cross3(sub3(b, a), sub3(c, a));
+                        Some(0.5 * dot3(n, n).sqrt())
+                    })
+                    .sum();
+                faces_sum = add3(faces_sum, scale3(c, area));
+                faces_area += area;
+                match body.face_surfaces()?.get(i as usize).copied().flatten() {
+                    Some(fieldcraft_geometry::FaceSurface::Cylinder { origin, axis: d, .. }) => {
+                        let len = dot3(d, d).sqrt();
+                        let d = scale3(d, 1.0 / len.max(1e-300));
+                        // The face centre's foot on the axis.
+                        let foot = add3(origin, scale3(d, dot3(sub3(c, origin), d)));
+                        let same = axis.is_none_or(|(o, a)| {
+                            let off = sub3(foot, o);
+                            let across = sub3(off, scale3(a, dot3(off, a)));
+                            dot3(cross3(a, d), cross3(a, d)) < 1e-12 && dot3(across, across).sqrt() <= 1e-6 * body.size().unwrap_or(1.0).max(1e-9)
+                        });
+                        round &= same;
+                        axis.get_or_insert((foot, d));
+                        circles.push(foot);
+                    }
+                    _ => round = false,
+                }
+            }
+            Entity::Edge(e) => {
+                let edges = body.edges()?;
+                let edge = edges.iter().find(|x| &x.name == e).ok_or_else(|| EngineError::Params(format!("body `{}` has no edge `{e}`", g.body)))?;
+                let (c, l) = polyline_centroid(&edge.points);
+                edges_sum = add3(edges_sum, scale3(c, l));
+                edges_length += l;
+                match circle_centre(&edge.points) {
+                    Some(c) => circles.push(c),
+                    None => round = false,
+                }
+            }
+            Entity::Vertex(_) | Entity::Body => {
+                return Err(EngineError::Params("geometry.centre takes one vertex, or faces and edges".into()));
+            }
+        }
+    }
+    // Arcs of one circle share a centre; faces of one axis were checked as they came.
+    let spread = circles.iter().map(|c| circles.first().map_or(0.0, |f| dot3(sub3(*c, *f), sub3(*c, *f)).sqrt())).fold(0.0f64, f64::max);
+    let size = geometry.first().and_then(|g| design.body(&g.body)).and_then(|b| b.size().ok()).unwrap_or(1.0).max(1e-9);
+    let edges_only = geometry.iter().all(|g| matches!(g.entity, Entity::Edge(_)));
+    if round && !circles.is_empty() && (!edges_only || spread <= 1e-6 * size) {
+        let point = match axis {
+            // Cylinder faces: the axis point at the mean of their centres' feet.
+            Some((_, d)) => {
+                let mean = scale3(circles.iter().fold([0.0; 3], |a, c| add3(a, *c)), 1.0 / circles.len() as f64);
+                let o = circles.first().copied().unwrap_or(mean);
+                add3(o, scale3(d, dot3(sub3(mean, o), d)))
+            }
+            None => circles.first().copied().unwrap_or_default(),
+        };
+        return Ok(json!({"point": point, "from": "circle"}));
+    }
+    let point = if faces_area > 0.0 {
+        scale3(faces_sum, 1.0 / faces_area)
+    } else if edges_length > 0.0 {
+        scale3(edges_sum, 1.0 / edges_length)
+    } else {
+        return Err(EngineError::Params("what is picked has no area or length to find a centre of".into()));
+    };
+    if !point.iter().all(|v| v.is_finite()) {
+        return Err(EngineError::Params("the centre is not a finite point".into()));
+    }
+    Ok(json!({"point": point, "from": "centroid"}))
+}
+
 fn body<'a>(s: &'a Session, p: &Value) -> Result<&'a Shape> {
    let name = p.get("body").and_then(Value::as_str).ok_or_else(|| EngineError::param("body", ProblemKind::NotAName))?;
    s.design.as_deref().and_then(|d| d.body(name)).ok_or_else(|| EngineError::Params(format!("no body `{name}` (open a design first)")))
@@ -168,6 +393,105 @@ pub(crate) fn body_mesh<'a>(s: &'a Session, p: &Value) -> Result<(&'a Shape, Sur
    Ok((shape, shape.tessellate(tolerance)?))
 }

+/// Most findings `geometry.check` lists.
+const MAX_FINDINGS: usize = 1000;
+
+fn check(s: &mut Session, p: &Value) -> Result<Value> {
+    use fieldcraft_geometry::check::{self, CheckOptions, Kind};
+    let shapes: Vec<&Shape> = match p.get("body") {
+        Some(_) => vec![body(s, p)?],
+        None => s.design.as_deref().map(|d| d.bodies.iter().collect()).unwrap_or_default(),
+    };
+    if shapes.is_empty() {
+        return Err(EngineError::Params("the design has no bodies to check".into()));
+    }
+    let size = match p.get("size") {
+        Some(v) => v.as_f64().filter(|x| *x > 0.0 && x.is_finite()).ok_or_else(|| EngineError::param("size", ProblemKind::NotPositive))?,
+        None => {
+            let mut smallest = f64::INFINITY;
+            for b in &shapes {
+                smallest = smallest.min(b.size()?);
+            }
+            smallest / 20.0
+        }
+    };
+    let fraction = |key: &str, default: f64| super::mesh::number_in(p, key, default, 0.0..=10.0);
+    let defaults = CheckOptions::new(size);
+    let options = CheckOptions {
+        size,
+        short_edge: fraction("short_edge", defaults.short_edge)?,
+        small_face: fraction("small_face", defaults.small_face)?,
+        sliver: fraction("sliver", defaults.sliver)?,
+        gap: fraction("gap", defaults.gap)?,
+        parallel_angle: super::mesh::number_in(p, "parallel_angle", defaults.parallel_angle.to_degrees(), 0.0..=60.0)?.to_radians(),
+    };
+    let mark = match p.get("mark") {
+        None => true,
+        Some(v) => v.as_bool().ok_or_else(|| EngineError::Params("`mark` must be true or false".into()))?,
+    };
+    let findings = check::check(&shapes, &options)?;
+    s.geometry_marks = s.design.as_ref().filter(|_| mark && !findings.is_empty()).map(|design| {
+        let marks = findings
+            .iter()
+            .map(|f| {
+                // A near pair's second face lies on the other body.
+                let on = |k: usize| if k == 1 { f.other_body.clone().unwrap_or_else(|| f.body.clone()) } else { f.body.clone() };
+                // A short edge is drawn itself: its faces can be large.
+                let faces = if f.kind == Kind::ShortEdge {
+                    Vec::new()
+                } else if f.kind == Kind::NearFaces {
+                    f.face_indices.iter().enumerate().map(|(k, &i)| (on(k), i)).collect()
+                } else {
+                    f.face_indices.iter().map(|&i| (f.body.clone(), i)).collect()
+                };
+                let small =
+                    matches!(f.kind, Kind::SmallFace | Kind::SliverFace).then(|| f.faces.first().map(|n| (f.body.clone(), n.clone()))).flatten();
+                crate::view::GeometryMark { faces, path: f.path.clone(), at: f.at, small }
+            })
+            .collect();
+        Arc::new(crate::view::GeometryMarks { design: Arc::downgrade(design), marks })
+    });
+    let counts: serde_json::Map<String, Value> =
+        Kind::ALL.iter().map(|k| (k.name().to_string(), json!(findings.iter().filter(|f| f.kind == *k).count()))).collect();
+    // The size to three decimals, without trailing zeros.
+    let shown = format!("{size:.3}").trim_end_matches('0').trim_end_matches('.').to_string();
+    let summary = if findings.is_empty() {
+        format!("nothing small against size {shown}")
+    } else {
+        let parts: Vec<String> = Kind::ALL
+            .iter()
+            .filter_map(|k| {
+                let n = findings.iter().filter(|f| f.kind == *k).count();
+                (n > 0).then(|| format!("{n} {}", k.name().replace('_', " ")))
+            })
+            .collect();
+        format!("{} against size {shown}", parts.join(", "))
+    };
+    let listed: Vec<Value> = findings
+        .iter()
+        .take(MAX_FINDINGS)
+        .map(|f| {
+            json!({
+                "kind": f.kind.name(),
+                "body": f.body,
+                "edge": f.edge,
+                "faces": f.faces,
+                "other_body": f.other_body,
+                "value": f.value,
+                "limit": f.limit,
+                "at": f.at,
+            })
+        })
+        .collect();
+    Ok(json!({
+        "size": size,
+        "counts": counts,
+        "summary": summary,
+        "findings": listed,
+        "truncated": findings.len() > MAX_FINDINGS,
+    }))
+}
+
 fn tessellate(s: &mut Session, p: &Value) -> Result<Value> {
    let (shape, mesh) = body_mesh(s, p)?;
    let mut per_face = vec![0usize; shape.faces().len()];
@@ -196,22 +520,230 @@ fn import_mesh(s: &mut Session, p: &Value) -> Result<Value> {
        .collect();
    s.surfaces.extend(surfaces.into_iter().map(Arc::new));
    s.sources.meshes.push(source);
-    Ok(json!({"path": path, "surfaces": added}))
+    // The model's stitches of surfaces by these names apply to them too.
+    let (_, failed) = super::stitch::restitch(s);
+    let mut reply = json!({"path": path, "surfaces": added});
+    let warnings: Vec<String> =
+        failed.into_iter().filter(|(_, why)| !why.starts_with("no surface")).map(|(n, why)| format!("stitch `{n}`: {why}")).collect();
+    if !warnings.is_empty()
+        && let Some(o) = reply.as_object_mut()
+    {
+        o.insert("warnings".into(), json!(warnings));
+    }
+    Ok(reply)
 }

 #[cfg(test)]
-mod tests {
+pub(crate) mod tests {
    use std::io::{Cursor, Write};

    use super::*;

-    fn package(model: &str) -> Vec<u8> {
+    /// A session with the design the SolidCraft `commands` build open.
+    pub(crate) fn design(commands: Value) -> (crate::tests::TempDir, Session) {
+        let bytes = fieldcraft_geometry::script_design(&json!({"commands": commands}).to_string()).unwrap();
+        let (dir, path) = crate::tests::design_file(&bytes);
+        let mut s = Session::default();
+        s.execute("geometry.open", &json!({"path": path})).unwrap();
+        (dir, s)
+    }
+
+    fn kinds(r: &Value) -> Vec<&str> {
+        r["findings"].as_array().unwrap().iter().map(|f| f["kind"].as_str().unwrap()).collect()
+    }
+
+    /// A plain block is clean at a size it can be meshed with; a 0.4 mm step on its top is a
+    /// sliver riser with two short edges, located on the step; the check changes nothing.
+    #[test]
+    fn check_finds_a_small_step() {
+        let (_dir, mut s) = design(json!([{"command": "solid.box", "params": {"length": 40, "width": 20, "height": 10, "body_name": "Base"}}]));
+        let clean = s.execute("geometry.check", &json!({"size": 5})).unwrap();
+        assert!(kinds(&clean).is_empty(), "{clean}");
+        assert_eq!(clean["summary"], "nothing small against size 5");
+        let (_dir, mut s) = design(json!([
+            {"command": "solid.box", "params": {"length": 40, "width": 20, "height": 10, "body_name": "Base"}},
+            {"command": "solid.box", "params": {"length": 20, "width": 20, "height": 10.4, "operation": "join", "targets": ["Base"]}},
+        ]));
+        let journal = s.journal.len();
+        let r = s.execute("geometry.check", &json!({"body": "Base", "size": 5})).unwrap();
+        assert_eq!(s.journal.len(), journal, "read-only");
+        assert_eq!(r["counts"]["short_edge"], 2, "{r}");
+        assert_eq!(r["counts"]["sliver_face"], 1, "{r}");
+        assert_eq!(r["counts"]["small_face"], 0, "{r}");
+        assert_eq!(r["counts"]["near_faces"], 0, "{r}");
+        let names: Vec<String> = s.execute("geometry.bodies", &json!({})).unwrap()[0]["faces"]
+            .as_array()
+            .unwrap()
+            .iter()
+            .map(|f| f["name"].as_str().unwrap().to_string())
+            .collect();
+        for f in r["findings"].as_array().unwrap() {
+            let at: Vec<f64> = f["at"].as_array().unwrap().iter().map(|v| v.as_f64().unwrap()).collect();
+            assert!((at[0] - 20.0).abs() < 1e-6 && at[2] >= 10.0 - 1e-6 && at[2] <= 10.4 + 1e-6, "on the riser: {f}");
+            assert!(f["faces"].as_array().unwrap().iter().all(|n| names.contains(&n.as_str().unwrap().to_string())), "{f}");
+            assert!(f["value"].as_f64().unwrap() < f["limit"].as_f64().unwrap());
+        }
+        let short = &r["findings"][0];
+        assert!((short["value"].as_f64().unwrap() - 0.4).abs() < 1e-6, "{short}");
+        assert!(short["edge"].is_string());
+        // The size is what makes the step small: at 1 mm it is a feature like any other.
+        let fine = s.execute("geometry.check", &json!({"size": 1})).unwrap();
+        assert!(kinds(&fine).is_empty(), "{fine}");
+    }
+
+    /// The findings are drawn in the picture: the sliver riser's faces in the marker colour, the
+    /// short edges as lines and a dot at each finding over everything; a clean check, `mark:
+    /// false` or another design takes them away.
+    #[test]
+    fn check_marks_its_findings_in_the_picture() {
+        let (_dir, mut s) = design(json!([
+            {"command": "solid.box", "params": {"length": 40, "width": 20, "height": 10, "body_name": "Base"}},
+            {"command": "solid.box", "params": {"length": 20, "width": 20, "height": 10.4, "operation": "join", "targets": ["Base"]}},
+        ]));
+        let p = crate::view::Palette::LIGHT;
+        let marked = |s: &Session| {
+            let (scene, _, _) = crate::view::scene(s, &p);
+            let faces = scene.tris.iter().filter(|t| t.color == p.marked).count();
+            let lines: Vec<_> = scene.on_top.iter().filter(|l| l.color == p.marked).collect();
+            let dots = lines.iter().filter(|l| l.a == l.b).count();
+            (faces, lines.len() - dots, dots)
+        };
+        assert_eq!(marked(&s), (0, 0, 0), "nothing checked yet");
+        let r = s.execute("geometry.check", &json!({"size": 5})).unwrap();
+        let (faces, edges, dots) = marked(&s);
+        assert!(faces > 0, "the riser's faces are marked");
+        assert!(edges >= 2, "the short edges are drawn: {edges}");
+        assert_eq!(dots, r["findings"].as_array().unwrap().len(), "a dot at each finding");
+        // Every marked triangle lies on the riser, x = 20, between z = 10 and 10.4.
+        let (scene, _, _) = crate::view::scene(&s, &p);
+        for t in scene.tris.iter().filter(|t| t.color == p.marked) {
+            assert!(t.p.iter().all(|v| (v.x - 20.0).abs() < 1e-6 && v.z > 10.0 - 1e-6 && v.z < 10.4 + 1e-6), "{t:?}");
+        }
+        s.execute("geometry.check", &json!({"size": 5, "mark": false})).unwrap();
+        assert_eq!(marked(&s), (0, 0, 0), "mark: false clears");
+        s.execute("geometry.check", &json!({"size": 5})).unwrap();
+        s.execute("geometry.check", &json!({"size": 1})).unwrap();
+        assert_eq!(marked(&s), (0, 0, 0), "a clean check clears");
+        s.execute("geometry.check", &json!({"size": 5})).unwrap();
+        assert!(s.execute("geometry.check", &json!({"size": 5, "mark": "yes"})).is_err());
+        assert!(marked(&s).2 > 0, "a failed check keeps the marks");
+        s.design = s.design.as_deref().map(|d| Arc::new(d.clone()));
+        assert_eq!(marked(&s), (0, 0, 0), "stale once another design is open");
+    }
+
+    /// Two bodies 0.5 mm apart: their facing faces are near faces; once they touch they are not.
+    #[test]
+    fn check_finds_a_gap_between_bodies() {
+        let (_dir, mut s) = design(json!([
+            {"command": "solid.box", "params": {"length": 10, "width": 10, "height": 10, "body_name": "A"}},
+            {"command": "solid.box", "params": {"length": 10, "width": 10, "height": 10, "corner": [0, 0, 10.5], "body_name": "B"}},
+        ]));
+        let r = s.execute("geometry.check", &json!({"size": 2.5})).unwrap();
+        assert_eq!(kinds(&r), ["near_faces"], "{r}");
+        let f = &r["findings"][0];
+        assert!((f["value"].as_f64().unwrap() - 0.5).abs() < 1e-6, "{f}");
+        let bodies = [f["body"].as_str().unwrap(), f["other_body"].as_str().unwrap()];
+        assert!(bodies.contains(&"A") && bodies.contains(&"B"), "{f}");
+        assert!(s.execute("geometry.check", &json!({"size": 2.5, "gap": 0.1})).unwrap()["findings"].as_array().unwrap().is_empty());
+        // Without a size the default is a twentieth of the smaller diagonal.
+        let d = s.execute("geometry.check", &json!({})).unwrap();
+        assert!((d["size"].as_f64().unwrap() - 300f64.sqrt() / 20.0).abs() < 1e-9, "{d}");
+    }
+
+    #[test]
+    fn check_rejects_hostile_parameters() {
+        let mut s = Session::default();
+        assert!(s.execute("geometry.check", &json!({})).is_err(), "needs a design");
+        let (_dir, mut s) = design(json!([{"command": "solid.box", "params": {"length": 10, "width": 10, "height": 10, "body_name": "A"}}]));
+        for p in [
+            json!({"size": 0}),
+            json!({"size": -1}),
+            json!({"size": "big"}),
+            json!({"size": 1e308, "gap": 1e308}),
+            json!({"short_edge": -1}),
+            json!({"sliver": 1e9}),
+            json!({"parallel_angle": 90}),
+            json!({"body": "Nope"}),
+            json!({"body": 3}),
+        ] {
+            assert!(s.execute("geometry.check", &p).is_err(), "{p}");
+        }
+    }
+
+    pub(crate) fn package(model: &str) -> Vec<u8> {
        let mut zip = zip::ZipWriter::new(Cursor::new(Vec::new()));
        zip.start_file("3D/3dmodel.model", zip::write::SimpleFileOptions::default()).unwrap();
        zip.write_all(model.as_bytes()).unwrap();
        zip.finish().unwrap().into_inner()
    }

+    /// The plate's hole (Ø10 at x = y = 15 through z 0..10): its faces give the axis point at
+    /// mid-depth, a rim arc its circle's centre, a corner vertex its point, a flat face its
+    /// centroid; datum points take the design's vertices by name.
+    #[test]
+    fn centres_of_holes_vertices_and_faces() {
+        use fieldcraft_geometry::FaceSurface;
+        use fieldcraft_geometry::sample::{Plate, plate_design};
+        let design = Arc::new(open_design(&plate_design(&Plate::default()).unwrap()).unwrap());
+        let mut s = Session { design: Some(design.clone()), ..Session::default() };
+        let body = &design.bodies[0];
+        let near = |v: &Value, p: [f64; 3]| {
+            let q: [f64; 3] = serde_json::from_value(v["point"].clone()).unwrap();
+            assert!((0..3).all(|k| (q[k] - p[k]).abs() < 1e-6), "{v} vs {p:?}");
+        };
+        let surfaces = body.face_surfaces().unwrap();
+        let hole: Vec<Value> = body
+            .faces()
+            .iter()
+            .zip(&surfaces)
+            .filter(|(_, s)| matches!(s, Some(FaceSurface::Cylinder { .. })))
+            .map(|(f, _)| json!({"body": body.name, "face": f.name}))
+            .collect();
+        assert_eq!(hole.len(), 2);
+        let r = s.execute("geometry.centre", &json!({"geometry": hole})).unwrap();
+        near(&r, [15.0, 15.0, 5.0]);
+        assert_eq!(r["from"], "circle");
+        let r = s.execute("geometry.centre", &json!({"geometry": [hole[0]]})).unwrap();
+        near(&r, [15.0, 15.0, 5.0]);
+        // A rim arc on top.
+        let edges = body.edges().unwrap();
+        let arc = edges.iter().find(|e| e.points.iter().all(|p| (p[2] - 10.0).abs() < 1e-9) && e.points.len() > 3).unwrap();
+        let r = s.execute("geometry.centre", &json!({"geometry": [{"body": body.name, "edge": arc.name}]})).unwrap();
+        near(&r, [15.0, 15.0, 10.0]);
+        assert_eq!(r["from"], "circle");
+        // The corner at the origin, and a datum point on it by name.
+        let corner = body.vertices().unwrap().into_iter().find(|v| v.point == [0.0; 3]).unwrap();
+        let r = s.execute("geometry.centre", &json!({"geometry": [{"body": body.name, "vertex": corner.name}]})).unwrap();
+        near(&r, [0.0; 3]);
+        s.execute("geometry.datum.point", &json!({"name": "P", "by": {"type": "vertex", "body": body.name, "vertex": corner.name}})).unwrap();
+        assert_eq!(s.model.datum("P").and_then(|d| d.point()), Some([0.0; 3]));
+        let listed = s.execute("geometry.bodies", &json!({})).unwrap();
+        assert!(listed[0]["vertices"].as_array().unwrap().iter().any(|v| v["name"] == corner.name.as_str()), "{listed}");
+        // The bottom face (z = 0): its centroid, off the hole.
+        let bottom = body
+            .faces()
+            .iter()
+            .zip(&surfaces)
+            .find(|(_, s)| matches!(s, Some(FaceSurface::Plane { normal, point }) if normal[2].abs() > 0.99 && point[2].abs() < 1e-9))
+            .unwrap()
+            .0;
+        let r = s.execute("geometry.centre", &json!({"geometry": [{"body": body.name, "face": bottom.name}]})).unwrap();
+        assert_eq!(r["from"], "centroid");
+        // Nodes, and what is refused.
+        s.model.set_node(1, [1.0, 2.0, 3.0]).unwrap();
+        s.model.set_node(2, [3.0, 2.0, 1.0]).unwrap();
+        near(&s.execute("geometry.centre", &json!({"nodes": [1, 2]})).unwrap(), [2.0, 2.0, 2.0]);
+        for bad in [
+            json!({}),
+            json!({"nodes": [99]}),
+            json!({"geometry": [{"body": "nope"}]}),
+            json!({"geometry": [{"body": body.name}]}),
+            json!({"nodes": "x"}),
+        ] {
+            assert!(s.execute("geometry.centre", &bad).is_err(), "{bad}");
+        }
+    }
+
    #[test]
    fn import_adds_tagged_surfaces_and_failures_change_nothing() {
        let dir = std::env::temp_dir().join(format!("fieldcraft-import-mesh-{}", std::process::id()));
@@ -220,27 +220,15 @@ pub(super) fn hex_blocks(s: &mut Session, p: &Value) -> Result<Value> {
        seeds: super::seeds::edge_seeds(s)?,
        ..HexOptions::default()
    };
-    let cm = hex_mesh_cells(&cells, &UniformSize(h), &options).map_err(|e| EngineError::Params(e.to_string()))?;
+    let cm = hex_mesh_cells(&cells, &UniformSize(h), &options).map_err(|e| match e {
+        fieldcraft_mesh::Error::Model(fieldcraft_model::Error::Cancelled) => EngineError::Model(fieldcraft_model::Error::Cancelled),
+        e => EngineError::Params(e.to_string()),
+    })?;
    let m = &cm.mesh;
    // Replace the cells' meshes (replace.rs); other bodies and the definitions stay.
    let model = &mut s.model;
    let cleared = super::replace::clear(model, inputs.iter().map(|b| b.name.as_str()));
-    let (first_node, first_element) = super::fresh_labels(model, m.nodes.len(), m.element_count())?;
-    for (i, xyz) in m.nodes.iter().enumerate() {
-        model.set_node(first_node + i as u32, *xyz)?;
-    }
-    let mut body_tags = Vec::with_capacity(inputs.len());
-    for b in &inputs {
-        body_tags.push(model.geometry_tag(&GeometryRef::body(b.name.as_str())?)?);
-    }
-    for e in 0..m.element_count() {
-        let cell = cm.element_cell.get(e).map_or(0, |&c| c as usize);
-        let nodes: Vec<u32> = m.element(e).unwrap_or(&[]).iter().map(|&i| first_node + i).collect();
-        let l = first_element + e as u32;
-        model.set_element(l, m.kind, nodes)?;
-        model.tag_element(l, body_tags.get(cell).copied().ok_or_else(|| EngineError::Params("element without a cell".into()))?)?;
-    }
-    tag_faces(model, &inputs, |e| cm.element_cell.get(e as usize).map_or(0, |&c| c as usize), &m.boundary, first_element)?;
+    add_cells(model, &inputs, &cm)?;
    let blocks: Vec<Value> =
        inputs.iter().zip(&cm.blocks).map(|(b, d)| json!({"body": b.name, "divisions": d, "elements": d.iter().product::<usize>()})).collect();
    let reply = json!({
@@ -349,7 +337,30 @@ pub(super) fn hex_body(p: &Value, b: &Input, method: HexMethod, quadratic: bool,
        seeds: b.seeds.clone(),
        ..HexOptions::default()
    };
-    hex_mesh(&surface, &b.surfaces, &UniformSize(h), &options).map_err(|e| EngineError::Params(format!("body `{}`: {e}", b.name)))
+    hex_mesh(&surface, &b.surfaces, &UniformSize(h), &options).map_err(|e| EngineError::of_body(&b.name, e))
+}
+
+/// Add a mesh of several cells (`inputs[c]` is cell `c`) after the model's largest labels, its
+/// nodes shared between the cells, tagging each element with its cell's body and the boundary
+/// element faces with the cell's B-rep faces.
+pub(super) fn add_cells(model: &mut Model, inputs: &[Input], cm: &fieldcraft_mesh::hex::CellsMesh) -> Result<()> {
+    let m = &cm.mesh;
+    let (first_node, first_element) = super::fresh_labels(model, m.nodes.len(), m.element_count())?;
+    for (i, xyz) in m.nodes.iter().enumerate() {
+        model.set_node(first_node + i as u32, *xyz)?;
+    }
+    let mut body_tags = Vec::with_capacity(inputs.len());
+    for b in inputs {
+        body_tags.push(model.geometry_tag(&GeometryRef::body(b.name.as_str())?)?);
+    }
+    for e in 0..m.element_count() {
+        let cell = cm.element_cell.get(e).map_or(0, |&c| c as usize);
+        let nodes: Vec<u32> = m.element(e).unwrap_or(&[]).iter().map(|&i| first_node + i).collect();
+        let l = first_element + e as u32;
+        model.set_element(l, m.kind, nodes)?;
+        model.tag_element(l, body_tags.get(cell).copied().ok_or_else(|| EngineError::Params("element without a cell".into()))?)?;
+    }
+    tag_faces(model, inputs, |e| cm.element_cell.get(e as usize).map_or(0, |&c| c as usize), &m.boundary, first_element)
 }

 /// Add one body's hex mesh after the model's largest labels, tagging the elements with the body
@@ -523,7 +534,7 @@ mod tests {
        let (_dir, mut s) = split_box(true);
        let before = s.model.clone();
        let e = s.execute("mesh.hex.blocks", &json!({"size": 2.5})).unwrap_err().to_string();
-        assert!(e.contains("do not conform") && e.contains("`Box`"), "{e}");
+        assert!(e.contains("do not conform") && e.contains("`Box.1`"), "{e}");
        assert_eq!(s.model, before);
        for p in [
            json!({"size": 0}),
@@ -40,7 +40,7 @@ pub const NODE_REMOVE: CommandSpec = CommandSpec {
 pub const ELEMENT_ADD: CommandSpec = CommandSpec {
    id: "mesh.element.add",
    label: "Add Element",
-    params: r#"{"label": 1, "kind": "rod2|beam2|tri3|tri6|quad4|quad8|tet4|tet10|wedge6|hex8|hex20", "nodes": [labels]} — adds or replaces"#,
+    params: r#"{"label": 1, "kind": "rod2|beam2|tri3|tri6|quad4|quad8|tet4|tet10|wedge6|pyramid5|hex8|hex20", "nodes": [labels]} — adds or replaces"#,
    form: Some(super::forms::ELEMENT_ADD),
    kind: CommandKind::Model,
    requires: &[Requirement::Nodes],
@@ -67,6 +67,26 @@ pub const QUALITY: CommandSpec = CommandSpec {
    run: quality_report,
 };

+pub const QUALITY_MARK: CommandSpec = CommandSpec {
+    id: "mesh.quality.mark",
+    label: "Mark Bad Elements",
+    params: r#"{"limits"?: {"scaled_jacobian": 0.2, "min_dihedral": 10, "max_dihedral": 165, "aspect_ratio": 10, "min_angle": 15, "max_angle": 165} (the defaults; given limits are merged over them, null drops one; any metric of mesh.quality may be limited: a floor for those where higher is better, a ceiling for max_dihedral, aspect_ratio, edge_ratio, max_angle and skew; angles in degrees), "elements"?: [labels] (default all)} — after meshing, marks the elements that fail a limit (and every solid not proven valid) as the element set `quality_marked`, replaced on every run and removed when none fail; the viewport and `fieldcraft-cli snapshot` draw its elements in the marker colour. Replies `summary`, `measured`, `marked`, `invalid`, the `limits` used and `elements` (worst first: not valid, then lowest scaled Jacobian; at most 1000, `truncated` says when more): each `label`, `kind`, `body`, `at` (its centroid), `valid` and `failed` ({metric, value, limit} per limit it fails). One undo step"#,
+    form: Some(super::forms::QUALITY_MARK),
+    kind: CommandKind::Model,
+    requires: &[Requirement::Mesh],
+    run: quality_mark,
+};
+
+pub const EXPORT_STL: CommandSpec = CommandSpec {
+    id: "mesh.export.stl",
+    label: "Export STL",
+    params: r#"{"path": "skin.stl", "set": "top", "format": "binary|ascii"} — writes the mesh's outer surface as STL: every solid element face no other solid shares, and the top side (face 1) of every shell; `set` (optional) writes only that set's element faces instead; `format` defaults to binary. Quadrilaterals are split in two, normals point out of the elements, and coordinates are rounded to single precision (STL stores f32). Replies {path, triangles, bytes}"#,
+    form: Some(super::forms::EXPORT_STL),
+    kind: CommandKind::Session,
+    requires: &[Requirement::Mesh],
+    run: export_stl,
+};
+
 pub const DELAUNAY_POINTS: CommandSpec = CommandSpec {
    id: "mesh.delaunay.points",
    label: "Delaunay of Points",
@@ -146,7 +166,7 @@ pub(super) fn surface_options(p: &Value, mesh: &SurfaceMesh) -> Result<SurfaceOp
 }

 /// An optional number in `range`.
-fn number_in(p: &Value, key: &str, default: f64, range: std::ops::RangeInclusive<f64>) -> Result<f64> {
+pub(super) fn number_in(p: &Value, key: &str, default: f64, range: std::ops::RangeInclusive<f64>) -> Result<f64> {
    let v = optional_number(p, key, default)?;
    if range.contains(&v) { Ok(v) } else { Err(EngineError::param(key, ProblemKind::NotInRange { min: *range.start(), max: *range.end() })) }
 }
@@ -235,10 +255,16 @@ pub(super) struct BodyTets {
    surface_volume: f64,
 }

+impl BodyTets {
+    pub(super) fn new(name: String, face_names: Vec<String>, mesh: QualityMesh, steiner: usize, cavities: usize, surface_volume: f64) -> Self {
+        BodyTets { name, face_names, mesh, steiner, cavities, surface_volume }
+    }
+}
+
 /// Mesh one body or imported surface; the model is not touched. With `several` bodies an error
 /// names the body.
 pub(super) fn mesh_body(
-    s: &Session,
+    design: Option<&fieldcraft_geometry::Design>,
    p: &Value,
    input: super::hex::Input,
    cdt: &CdtOptions,
@@ -249,10 +275,12 @@ pub(super) fn mesh_body(
    let mesh = || -> Result<BodyTets> {
        // The exact faces of a design body; an imported surface keeps to its triangles.
        let analytic = match p.get("surface") {
-            None => s.design.as_deref().and_then(|d| d.body(&input.name)).map(analytic_surfaces).unwrap_or_default(),
+            None => design.and_then(|d| d.body(&input.name)).map(analytic_surfaces).unwrap_or_default(),
            Some(_) => Vec::new(),
        };
+        fieldcraft_model::progress::stage(&format!("{}: boundary", input.name), None, "");
        let surface = BoundarySurface::new(&input.mesh.positions, &input.mesh.triangles, &input.mesh.tri_face, &surface_options(p, &input.mesh)?)?;
+        fieldcraft_model::progress::stage(&format!("{}: Delaunay", input.name), None, "");
        let tets = tetrahedralize(&surface, cdt)?;
        let mesh = if quality {
            let options = QualityOptions { seeds: input.seeds.clone(), ..options.clone() };
@@ -269,7 +297,7 @@ pub(super) fn mesh_body(
            surface_volume: surface.volume(),
        })
    };
-    mesh().map_err(|e| if several { EngineError::Params(format!("body `{}`: {e}", input.name)) } else { e })
+    mesh().map_err(|e| if several && !e.is_cancelled() { EngineError::Params(format!("body `{}`: {e}", input.name)) } else { e })
 }

 fn tet_generate(s: &mut Session, p: &Value) -> Result<Value> {
@@ -281,7 +309,7 @@ fn tet_generate(s: &mut Session, p: &Value) -> Result<Value> {
    let several = inputs.len() > 1;
    let mut meshed = Vec::with_capacity(inputs.len());
    for input in inputs {
-        meshed.push(mesh_body(s, p, input, &cdt_options, &options, quality, several)?);
+        meshed.push(mesh_body(s.design.as_deref(), p, input, &cdt_options, &options, quality, several)?);
    }

    // Replace the bodies' meshes (replace.rs); other bodies and the definitions stay.
@@ -551,6 +579,53 @@ fn number(v: f64) -> Value {
    if v.is_finite() { json!(v) } else { json!(if v > 0.0 { "inf" } else { "-inf" }) }
 }

+fn export_stl(s: &mut Session, p: &Value) -> Result<Value> {
+    let set: Option<String> = super::opt(p, "set")?;
+    let format: Option<String> = super::opt(p, "format")?;
+    let ascii = match format.as_deref() {
+        None | Some("binary") => false,
+        Some("ascii") => true,
+        Some(other) => {
+            let shown: String = other.chars().take(32).collect();
+            return Err(EngineError::Params(format!("unknown STL format `{shown}`; known: binary, ascii")));
+        }
+    };
+    let path = super::file_param(s, p, "path", fieldcraft_io::roots::Access::Write)?;
+    let m = &s.model;
+    if m.elements().is_empty() {
+        return Err(EngineError::Params("the mesh has no elements".into()));
+    }
+    let faces = match &set {
+        Some(name) => {
+            let shown: String = name.chars().take(64).collect();
+            if !m.sets().contains_key(name) {
+                return Err(EngineError::Params(format!("no set `{shown}`")));
+            }
+            let faces = m.resolve_set(name)?.faces;
+            if faces.is_empty() {
+                return Err(EngineError::Params(format!("set `{shown}` has no element faces")));
+            }
+            faces
+        }
+        None => {
+            let faces = m.skin_faces();
+            if faces.is_empty() {
+                return Err(EngineError::Params("the mesh has only line elements: no surface to write".into()));
+            }
+            faces
+        }
+    };
+    let bytes = if ascii {
+        let name = std::path::Path::new(&path).file_stem().map(|n| n.to_string_lossy().into_owned()).unwrap_or_default();
+        fieldcraft_io::stl::write_ascii(m, &faces, &name)?.into_bytes()
+    } else {
+        fieldcraft_io::stl::write_binary(m, &faces)?
+    };
+    let triangles = fieldcraft_io::stl::triangles(m, &faces)?.len();
+    fieldcraft_io::fs::write_atomic(std::path::Path::new(&path), &bytes, false)?;
+    Ok(json!({"path": path, "triangles": triangles, "bytes": bytes.len()}))
+}
+
 fn quality_report(s: &mut Session, p: &Value) -> Result<Value> {
    let bins = match p.get("bins") {
        None => 10,
@@ -591,6 +666,103 @@ fn quality_report(s: &mut Session, p: &Value) -> Result<Value> {
    }))
 }

+/// The element set `mesh.quality.mark` keeps the marked elements in.
+pub const MARKED_SET: &str = "quality_marked";
+
+/// The default limits of `mesh.quality.mark`.
+const MARK_LIMITS: [(quality::Metric, f64); 6] = [
+    (quality::Metric::ScaledJacobian, 0.2),
+    (quality::Metric::MinDihedral, 10.0),
+    (quality::Metric::MaxDihedral, 165.0),
+    (quality::Metric::AspectRatio, 10.0),
+    (quality::Metric::MinAngle, 15.0),
+    (quality::Metric::MaxAngle, 165.0),
+];
+
+/// Most marked elements `mesh.quality.mark` lists.
+const MAX_MARKED_LISTED: usize = 1000;
+
+fn quality_mark(s: &mut Session, p: &Value) -> Result<Value> {
+    let mut limits: std::collections::BTreeMap<quality::Metric, f64> = MARK_LIMITS.into_iter().collect();
+    match p.get("limits") {
+        None | Some(Value::Null) => {}
+        Some(Value::Object(given)) => {
+            for (name, v) in given {
+                let metric = quality::Metric::parse(name).ok_or_else(|| {
+                    let known: Vec<&str> = quality::Metric::ALL.iter().map(|m| m.name()).collect();
+                    EngineError::Params(format!("no quality metric `{}` (one of {})", name.chars().take(40).collect::<String>(), known.join(", ")))
+                })?;
+                match v {
+                    Value::Null => {
+                        limits.remove(&metric);
+                    }
+                    v => {
+                        let limit = v
+                            .as_f64()
+                            .filter(|x| x.is_finite())
+                            .ok_or_else(|| EngineError::Params(format!("the limit of `{name}` must be a number")))?;
+                        limits.insert(metric, limit);
+                    }
+                }
+            }
+        }
+        Some(_) => return Err(EngineError::Params("`limits` must be an object of metric names and numbers".into())),
+    }
+    let selection = match p.get("elements") {
+        None => None,
+        Some(_) => Some(labels(p, "elements", MAX_ELEMENTS)?),
+    };
+    let limits: Vec<(quality::Metric, f64)> = limits.into_iter().collect();
+    let (measured, marked) = quality::mark_elements(&s.model, selection.as_deref(), &limits)?;
+    let set = fieldcraft_model::Set { elements: marked.iter().map(|m| m.label).collect(), ..Default::default() };
+    if set.elements.is_empty() {
+        if s.model.set(MARKED_SET).is_some() {
+            s.model.remove_set(MARKED_SET)?;
+        }
+    } else if s.model.set(MARKED_SET).is_some() {
+        s.model.replace_set(MARKED_SET, set)?;
+    } else {
+        s.model.add_set(MARKED_SET, set)?;
+    }
+    let invalid = marked.iter().filter(|m| m.is_invalid()).count();
+    let c = s.model.classification();
+    let body = |label: u32| c.elements().get(&label).and_then(|t| t.region).and_then(|r| c.entity(r)).map(|g| g.body.clone());
+    let elements: Vec<Value> = marked
+        .iter()
+        .take(MAX_MARKED_LISTED)
+        .map(|m| {
+            json!({
+                "label": m.label,
+                "kind": m.kind.name(),
+                "body": body(m.label),
+                "at": m.centroid,
+                "valid": m.validity.map(|v| v == quality::Validity::Valid),
+                "failed": m.failed.iter().map(|(metric, v, limit)| json!({"metric": metric.name(), "value": number(*v), "limit": limit})).collect::<Vec<_>>(),
+            })
+        })
+        .collect();
+    let mut summary = format!("{} of {measured} elements marked", marked.len());
+    if invalid > 0 {
+        summary.push_str(&format!(", {invalid} not valid"));
+    }
+    if let Some(worst) = marked.first().and_then(|m| m.scaled_jacobian) {
+        summary.push_str(&format!("; worst scaled Jacobian {worst:.3}"));
+    }
+    if !marked.is_empty() {
+        summary.push_str(&format!(" (set {MARKED_SET})"));
+    }
+    Ok(json!({
+        "summary": summary,
+        "set": (!marked.is_empty()).then_some(MARKED_SET),
+        "measured": measured,
+        "marked": marked.len(),
+        "invalid": invalid,
+        "limits": limits.iter().map(|(m, v)| (m.name().to_string(), json!(v))).collect::<serde_json::Map<_, _>>(),
+        "elements": elements,
+        "truncated": marked.len() > MAX_MARKED_LISTED,
+    }))
+}
+
 /// A quality report in a line, for the status bar and the CLI: the elements measured, how many
 /// are invalid or undetermined, and the scaled Jacobian's minimum and mean.
 fn quality_summary(r: &QualityReport) -> String {
@@ -669,6 +841,63 @@ fn surface_check(s: &mut Session, p: &Value) -> Result<Value> {

 #[cfg(test)]
 mod tests {
+    #[test]
+    fn export_stl_writes_the_skin_or_a_set() {
+        let dir = std::env::temp_dir().join(format!("fieldcraft-stl-{}", std::process::id()));
+        std::fs::create_dir_all(&dir).unwrap();
+        let path = dir.join("skin.stl");
+        let path_str = path.to_string_lossy().into_owned();
+        let mut s = Session::default();
+        assert!(s.execute("mesh.export.stl", &json!({"path": path_str})).is_err(), "no mesh");
+        s.execute("file.sample", &json!({"name": "cantilever"})).unwrap();
+        let journal = s.journal.len();
+        let out = s.execute("mesh.export.stl", &json!({"path": path_str})).unwrap();
+        let bytes = std::fs::read(&path).unwrap();
+        assert!(!bytes.starts_with(b"solid"));
+        let skin = fieldcraft_io::stl::triangles(&s.model, &s.model.skin_faces()).unwrap().len();
+        assert!(skin >= s.model.skin_faces().len() && skin > 0);
+        assert_eq!(out["triangles"], skin);
+        assert_eq!(bytes.len(), 84 + 50 * skin);
+        assert_eq!(out["bytes"], bytes.len());
+        assert_eq!(s.journal.len(), journal, "exporting does not change the model");
+
+        // A set with faces writes only those; one without faces, or an unknown one, is refused.
+        let faces = s.model.skin_faces();
+        let two: Vec<serde_json::Value> = faces.iter().take(2).map(|f| json!({"element": f.element, "face": f.face})).collect();
+        let first = *s.model.elements().keys().next().unwrap();
+        s.execute("model.set.create", &json!({"name": "stl_faces", "faces": two})).unwrap();
+        s.execute("model.set.create", &json!({"name": "stl_elements", "elements": [first]})).unwrap();
+        let out = s.execute("mesh.export.stl", &json!({"path": path_str, "set": "stl_faces"})).unwrap();
+        assert_eq!(out["triangles"], fieldcraft_io::stl::triangles(&s.model, &faces[..2]).unwrap().len());
+        let other = dir.join("other.stl").to_string_lossy().into_owned();
+        let e = s.execute("mesh.export.stl", &json!({"path": other, "set": "nope"})).unwrap_err().to_string();
+        assert!(e.contains("no set `nope`"), "{e}");
+        let e = s.execute("mesh.export.stl", &json!({"path": other, "set": "stl_elements"})).unwrap_err().to_string();
+        assert!(e.contains("has no element faces"), "{e}");
+        let e = s.execute("mesh.export.stl", &json!({"path": other, "format": "obj"})).unwrap_err().to_string();
+        assert!(e.contains("known: binary, ascii"), "{e}");
+        assert!(!dir.join("other.stl").exists());
+
+        let out = s.execute("mesh.export.stl", &json!({"path": path_str, "format": "ascii"})).unwrap();
+        let text = std::fs::read_to_string(&path).unwrap();
+        assert!(text.starts_with("solid skin\n"));
+        assert_eq!(text.matches("facet normal").count(), skin);
+        assert_eq!(out["triangles"], skin);
+        let _ = std::fs::remove_dir_all(&dir);
+    }
+
+    #[test]
+    fn export_stl_refuses_a_mesh_of_lines() {
+        let mut s = Session::default();
+        s.execute("mesh.node.add", &json!({"label": 1, "xyz": [0, 0, 0]})).unwrap();
+        s.execute("mesh.node.add", &json!({"label": 2, "xyz": [1, 0, 0]})).unwrap();
+        s.execute("mesh.element.add", &json!({"label": 1, "kind": "rod2", "nodes": [1, 2]})).unwrap();
+        let path = std::env::temp_dir().join(format!("fieldcraft-stl-lines-{}.stl", std::process::id()));
+        let e = s.execute("mesh.export.stl", &json!({"path": path.to_string_lossy()})).unwrap_err().to_string();
+        assert!(e.contains("only line elements"), "{e}");
+        assert!(!path.exists());
+    }
+
    use serde_json::json;

    use crate::Session;
@@ -709,6 +938,73 @@ mod tests {
        }
    }

+    fn mark_session() -> Session {
+        let mut s = Session::default();
+        let corners = json!([[0, 0, 0], [2, 0, 0], [2, 1, 0], [0, 1, 0], [0, 0, 1], [2, 0, 1], [2, 1, 1], [0, 1, 1]]);
+        s.execute("mesh.block", &json!({"body": "Bar", "kind": "hex8", "corners": corners, "divisions": [2, 1, 1]})).unwrap();
+        s
+    }
+
+    /// Two good hexes mark nothing; a corner pulled in marks its element, located, as the set
+    /// the viewport draws; looser limits empty it; undo brings it back.
+    #[test]
+    fn marks_bad_elements_as_a_set() {
+        let mut s = mark_session();
+        let r = s.execute("mesh.quality.mark", &json!({})).unwrap();
+        assert_eq!((r["measured"].as_u64(), r["marked"].as_u64()), (Some(2), Some(0)), "{r}");
+        assert!(s.model.set(super::MARKED_SET).is_none() && r["set"].is_null());
+        assert_eq!(r["limits"]["scaled_jacobian"], 0.2);
+        // Pull the far top corner of the second hex nearly onto its middle.
+        let (&corner, _) = s.model.nodes().iter().find(|(_, n)| n.xyz == [2.0, 1.0, 1.0]).unwrap();
+        let (&bad, _) = s.model.elements().iter().find(|(_, e)| e.nodes.contains(&corner)).unwrap();
+        s.execute("mesh.node.add", &json!({"label": corner, "xyz": [1.7, 0.7, 0.7]})).unwrap();
+        let r = s.execute("mesh.quality.mark", &json!({})).unwrap();
+        assert_eq!((r["marked"].as_u64(), r["invalid"].as_u64()), (Some(1), Some(0)), "{r}");
+        assert_eq!(r["set"], super::MARKED_SET);
+        let e = &r["elements"][0];
+        assert_eq!((e["label"].as_u64(), e["kind"].as_str(), e["body"].as_str()), (Some(bad as u64), Some("hex8"), Some("Bar")), "{e}");
+        assert!(e["failed"].as_array().unwrap().iter().any(|f| f["metric"] == "scaled_jacobian"), "{e}");
+        let at: Vec<f64> = e["at"].as_array().unwrap().iter().map(|v| v.as_f64().unwrap()).collect();
+        assert!(at[0] > 1.0 && at[0] < 2.0, "{at:?}");
+        assert!(r["summary"].as_str().unwrap().starts_with("1 of 2 elements marked"), "{r}");
+        assert_eq!(s.model.set(super::MARKED_SET).unwrap().elements, [bad]);
+        assert_eq!(crate::view::marked(&s).into_iter().collect::<Vec<_>>(), [bad]);
+        // The picture draws its faces in the marker colour, and only its.
+        let p = crate::view::Palette::LIGHT;
+        let (scene, _, _) = crate::view::scene(&s, &p);
+        let red = scene.tris.iter().filter(|t| t.color == p.marked).count();
+        assert_eq!(red, 5 * 2, "the bad hex's outer faces (all but the shared one), as triangles");
+        // Without limits the (valid) element passes and the set goes.
+        let all_off = json!({"limits": {"scaled_jacobian": null, "min_dihedral": null, "max_dihedral": null, "aspect_ratio": null, "min_angle": null, "max_angle": null}});
+        let r = s.execute("mesh.quality.mark", &all_off).unwrap();
+        assert_eq!(r["marked"], 0, "{r}");
+        assert!(s.model.set(super::MARKED_SET).is_none());
+        s.execute("edit.undo", &json!({})).unwrap();
+        assert_eq!(s.model.set(super::MARKED_SET).unwrap().elements, [bad], "undo restores the marks");
+        // Only the elements asked about.
+        let other = s.model.elements().keys().copied().find(|l| *l != bad).unwrap();
+        assert_eq!(s.execute("mesh.quality.mark", &json!({"elements": [other]})).unwrap()["marked"], 0);
+    }
+
+    #[test]
+    fn mark_rejects_hostile_parameters() {
+        let mut s = Session::default();
+        assert!(s.execute("mesh.quality.mark", &json!({})).is_err(), "needs a mesh");
+        let mut s = mark_session();
+        for p in [
+            json!({"limits": {"nope": 1}}),
+            json!({"limits": {"scaled_jacobian": "low"}}),
+            json!({"limits": {"scaled_jacobian": true}}),
+            json!({"limits": [0.2]}),
+            json!({"limits": {"x".repeat(10000): 1}}),
+            json!({"elements": [0]}),
+            json!({"elements": [99]}),
+            json!({"elements": "all"}),
+        ] {
+            assert!(s.execute("mesh.quality.mark", &p).is_err(), "{p}");
+        }
+    }
+
    #[test]
    fn reports_quality_and_inverted_elements() {
        let mut s = Session::default();
@@ -785,7 +1081,7 @@ mod tests {
            SurfaceMesh { positions: p.clone(), triangles: t.clone(), tri_face: vec![0, 1, 1, 1], weld_distance: 0.0, ..SurfaceMesh::default() };
        let open = SurfaceMesh { positions: p, triangles: t[..3].to_vec(), tri_face: vec![0, 1, 1], weld_distance: 0.0, ..SurfaceMesh::default() };
        for mesh in [tet, open] {
-            s.surfaces.push(Arc::new(TaggedSurface { name: "Tet".into(), mesh, faces: 2 }));
+            s.surfaces.push(Arc::new(TaggedSurface { name: "Tet".into(), mesh, faces: 2, original: None }));
        }
        let r = s.execute("mesh.surface.check", &json!({"surface": 0, "feature_angle": 180})).unwrap();
        assert_eq!((r["valid"].clone(), r["feature_edges"].clone()), (json!(true), json!({"face_boundary": 3, "sharp": 0})));
@@ -894,6 +1190,35 @@ mod tests {
        assert!(e.starts_with("body `Box"), "{e}");
    }

+    /// Persistent names grow with the design's split history: a tray floor split by joined ribs
+    /// names every split, past the old 256-character cap. Such a design meshes, and a set on that
+    /// face resolves by its full name, again after a remesh (#374).
+    #[test]
+    fn long_persistent_face_names_mesh_and_resolve() {
+        let mut commands = vec![
+            json!({"command": "solid.box", "params": {"length": 40, "width": 30, "height": 20, "corner": [0, 0, 0], "body_name": "Case"}}),
+            json!({"command": "solid.shell", "params": {"faces": [[20, 15, 20]], "thickness": 2, "direction": "inside", "body": "Case"}}),
+        ];
+        // Ribs across the floor split it into strips, each named by every split before it.
+        for x in (3..=36).step_by(3) {
+            commands.push(json!({"command": "solid.box", "params": {"length": 1, "width": 26, "height": 5, "corner": [x, 2, 2], "operation": "join", "targets": ["Case"]}}));
+        }
+        let bytes = fieldcraft_geometry::script_design(&json!({"commands": commands}).to_string()).unwrap();
+        let (_dir, path) = crate::tests::design_file(&bytes);
+        let mut s = Session::default();
+        s.execute("geometry.open", &json!({"path": path})).unwrap();
+        let bodies = s.execute("geometry.bodies", &json!({})).unwrap();
+        let long = bodies[0]["faces"].as_array().unwrap().iter().filter_map(|f| f["name"].as_str()).max_by_key(|n| n.len()).unwrap().to_string();
+        assert!(long.len() > 256, "the fixture needs a face name past the old cap: {long}");
+        s.execute("mesh.tet.generate", &json!({"body": "Case"})).unwrap();
+        s.execute("model.set.create", &json!({"name": "floor", "geometry": [{"body": "Case", "face": long}]})).unwrap();
+        let first = s.model.resolve_set("floor").unwrap();
+        assert!(!first.faces.is_empty());
+        s.execute("mesh.tet.generate", &json!({"body": "Case", "tolerance": 0.5})).unwrap();
+        let again = s.model.resolve_set("floor").unwrap();
+        assert!(!again.faces.is_empty(), "the set follows the remesh by the full name");
+    }
+
    /// The quality report's one-line summary counts the inverted elements.
    #[test]
    fn quality_summary_counts_invalid_elements() {
@@ -989,7 +1314,7 @@ mod tests {
        let open = SurfaceMesh { positions: p, triangles: t[..3].to_vec(), tri_face: vec![0, 1, 1], weld_distance: 0.0, ..SurfaceMesh::default() };
        let mut s = Session::default();
        for mesh in [tet, open] {
-            s.surfaces.push(Arc::new(TaggedSurface { name: "Tet".into(), mesh, faces: 2 }));
+            s.surfaces.push(Arc::new(TaggedSurface { name: "Tet".into(), mesh, faces: 2, original: None }));
        }
        let r = s.execute("mesh.tet.generate", &json!({"surface": 0, "quality": false})).unwrap();
        assert_eq!((r["elements"].clone(), r["nodes"].clone(), r["boundary_faces"].clone()), (json!(1), json!(4), json!(4)));
@@ -9,8 +9,10 @@
 use crate::schema::ProblemKind;
 use std::collections::{BTreeMap, BTreeSet};

-use fieldcraft_geometry::Shape;
+use fieldcraft_geometry::{Design, Shape};
 use fieldcraft_mesh::mirror::{mirror, reflected_edges, reflected_faces};
+use fieldcraft_mesh::surface::{BoundarySurface, SurfaceOptions};
+use fieldcraft_mesh::tet::geometry::Tessellation;
 use fieldcraft_model::geometry::Entity;
 use fieldcraft_model::{ElementFace, GeometryRef, Model};
 use serde_json::{Value, json};
@@ -21,7 +23,7 @@ use crate::{CommandKind, CommandSpec, EngineError, Result, Session};
 pub const MIRROR: CommandSpec = CommandSpec {
    id: "mesh.mirror",
    label: "Mirror Mesh",
-    params: r#"{"plane": "Sym" (a datum plane) or {"point": [x, y, z], "normal": [nx, ny, nz]}, "bodies": ["Part/a"] (default: every body the mesh is tagged with), "as": {"Part/a": "Part/b"} (optional: the body each image is; default the design's body at the reflected place, else "<body>/mirror")} — replaces each image body's mesh (as mesh.tet.generate) with the reflection of the bodies' elements (tet4, tet10, wedge6, hex8, hex20) across the plane: each copy right-handed (its nodes in reflected order), the copies of the nodes on the plane merged with them so the mesh is conforming there, geometry tags carried to the image (its body, and on it the faces the reflected faces lie on, so sets by face name select both halves). Reports the elements and nodes added, the nodes shared on the plane and each image's body"#,
+    params: r#"{"plane": "Sym" (a datum plane) or {"point": [x, y, z], "normal": [nx, ny, nz]}, "bodies": ["Part/a"] (default: every body the mesh is tagged with), "as": {"Part/a": "Part/b"} (optional: the body each image is; default the design's body at the reflected place, else "<body>/mirror")} — replaces each image body's mesh (as mesh.tet.generate) with the reflection of the bodies' elements (tet4, tet10, wedge6, pyramid5, hex8, hex20) across the plane: each copy right-handed (its nodes in reflected order), the copies of the nodes on the plane merged with them so the mesh is conforming there, geometry tags carried to the image (its body, and on it the faces the reflected faces lie on, so sets by face name select both halves). Reports the elements and nodes added, the nodes shared on the plane and each image's body"#,
    form: Some(super::forms::MIRROR),
    kind: CommandKind::Model,
    requires: &[Requirement::Mesh],
@@ -42,11 +44,7 @@ fn not_a_plane() -> EngineError {
 /// The plane: a datum plane by name, or a point and a normal.
 fn plane(s: &Session, p: &Value) -> Result<([f64; 3], [f64; 3])> {
    match p.get("plane") {
-        Some(Value::String(name)) => s
-            .model
-            .datum(name)
-            .and_then(|d| d.plane())
-            .ok_or_else(|| EngineError::Params(format!("no datum plane `{}`", name.chars().take(64).collect::<String>()))),
+        Some(Value::String(name)) => super::datum::datum_plane_of(&s.model, name),
        Some(v @ Value::Object(_)) => match (super::xyz(v, "point"), super::xyz(v, "normal")) {
            (Ok(point), Ok(normal)) => Ok((point, normal)),
            _ => Err(not_a_plane()),
@@ -56,6 +54,11 @@ fn plane(s: &Session, p: &Value) -> Result<([f64; 3], [f64; 3])> {
    }
 }

+/// The distance between two points.
+fn dist(a: [f64; 3], b: [f64; 3]) -> f64 {
+    (0..3).map(|k| (a[k] - b[k]).powi(2)).sum::<f64>().sqrt()
+}
+
 fn reflect(x: [f64; 3], point: [f64; 3], n: [f64; 3]) -> [f64; 3] {
    let d: f64 = (0..3).map(|i| (x[i] - point[i]) * n[i]).sum();
    [x[0] - 2.0 * d * n[0], x[1] - 2.0 * d * n[1], x[2] - 2.0 * d * n[2]]
@@ -169,7 +172,7 @@ fn mirror_mesh(s: &mut Session, p: &Value) -> Result<Value> {
    let cleared = super::replace::clear(model, image.values().map(|(name, _)| name.as_str()));
    let before = model.clone();
    let r = mirror(model, &region, point, n, ON_PLANE * diagonal).map_err(|e| EngineError::Params(e.to_string()))?;
-    tag_image(model, &before, &r, &image, point, n, diagonal)?;
+    tag_image(model, &before, &r, &image, design.as_deref(), point, n, diagonal)?;
    let added_nodes = model.nodes().len() - before.nodes().len();
    let images: Vec<Value> = image.iter().map(|(b, (t, shape))| json!({"body": b, "image": t, "in_design": shape.is_some()})).collect();
    let reply = json!({
@@ -189,50 +192,66 @@ fn tag_image(
    before: &Model,
    r: &fieldcraft_mesh::mirror::Mirrored,
    image: &BTreeMap<String, (String, Option<&Shape>)>,
+    design: Option<&Design>,
    point: [f64; 3],
    n: [f64; 3],
    diagonal: f64,
 ) -> Result<()> {
    let c = before.classification();
    let entity = |t: u32| c.entity(t).cloned();
-    // A source face's image: by the image body's face under its reflected centroid, one lookup per
-    // face name (the first element face of it stands for all).
-    let mut face_points: BTreeMap<(String, String), [f64; 3]> = BTreeMap::new();
-    for (&e, tags) in c.elements() {
-        if !r.elements.contains_key(&e) {
-            continue;
-        }
-        for (&f, &t) in &tags.faces {
-            let Some(GeometryRef { body, entity: Entity::Face(name) }) = entity(t) else { continue };
-            if face_points.contains_key(&(body.clone(), name.clone())) {
-                continue;
+    // Each image body's faces, to find the one each reflected boundary face lies on. A source
+    // face's image is the set of image faces its own reflection covers (sampled at its
+    // triangles' centres: one face for an exact mirror, pieces where the image is split
+    // differently); each element face goes to the one of them nearest its reflected centre. So
+    // an element face the mesher gave a face narrower than the elements (its centre on a
+    // neighbour) keeps that face's image.
+    let tolerance = (1e-3 * diagonal).max(1e-4);
+    let mut targets: BTreeMap<&str, (Tessellation, Vec<String>)> = BTreeMap::new();
+    for (target, shape) in image.values() {
+        let Some(shape) = shape else { continue };
+        let mesh = shape.tessellate(tolerance)?;
+        let options = SurfaceOptions { weld_distance: mesh.weld_distance, ..SurfaceOptions::default() };
+        let surface = BoundarySurface::new(&mesh.positions, &mesh.triangles, &mesh.tri_face, &options)
+            .map_err(|e| EngineError::Params(format!("body `{target}`: {e}")))?;
+        let names = shape.faces().iter().map(|f| f.name.clone()).collect();
+        targets.insert(target.as_str(), (Tessellation::new(&surface, Vec::new()), names));
+    }
+    // The image faces each source face's reflection covers, by (source body, face name).
+    let mut covers: BTreeMap<(String, String), Vec<u32>> = BTreeMap::new();
+    for (body, (target, _)) in image {
+        let (Some(shape), Some((tess, _))) = (design.and_then(|d| d.body(body)), targets.get(target.as_str())) else { continue };
+        let mesh = shape.tessellate(tolerance)?;
+        let at = |v: u32| mesh.positions.get(v as usize).copied().unwrap_or_default();
+        for (t, &f) in mesh.triangles.iter().zip(&mesh.tri_face) {
+            let Some(name) = shape.faces().get(f as usize).map(|x| x.name.clone()) else { continue };
+            let centre = [0, 1, 2].map(|k| (at(t[0])[k] + at(t[1])[k] + at(t[2])[k]) / 3.0);
+            let Some(hit) = tess.nearest_face(reflect(centre, point, n)) else { continue };
+            let list = covers.entry((body.clone(), name)).or_default();
+            if !list.contains(&hit) {
+                list.push(hit);
            }
-            let Some(nodes) = before.face_nodes(ElementFace { element: e, face: f }) else { continue };
+        }
+    }
+    let image_face = |e: u32, f: u8, body: &str, name: &str| -> Option<(String, String)> {
+        let (target, _) = image.get(body)?;
+        let mapped = targets.get(target.as_str()).and_then(|(tess, names)| {
+            let nodes = before.face_nodes(ElementFace { element: e, face: f })?;
            let pts: Vec<[f64; 3]> = nodes.iter().filter_map(|n| before.node(*n).map(|x| x.xyz)).collect();
            let k = pts.len().max(1) as f64;
-            let centre = [0, 1, 2].map(|i| pts.iter().map(|p| p[i]).sum::<f64>() / k);
-            face_points.insert((body, name), reflect(centre, point, n));
-        }
-    }
-    let mut face_names: BTreeMap<(String, String), (String, String)> = BTreeMap::new();
-    let mut by_body: BTreeMap<String, Vec<(String, [f64; 3])>> = BTreeMap::new();
-    for ((body, name), p) in &face_points {
-        by_body.entry(body.clone()).or_default().push((name.clone(), *p));
-    }
-    for (body, faces) in by_body {
-        let Some((target, shape)) = image.get(&body) else { continue };
-        let found = match shape {
-            Some(shape) => {
-                let pts: Vec<[f64; 3]> = faces.iter().map(|(_, p)| *p).collect();
-                shape.nearest_faces(&pts, (1e-3 * diagonal).max(1e-4))?
-            }
-            None => vec![None; faces.len()],
-        };
-        for ((name, _), f) in faces.iter().zip(found) {
-            let mapped = f.and_then(|f| shape.and_then(|s| s.faces().get(f as usize))).map_or_else(|| name.clone(), |x| x.name.clone());
-            face_names.insert((body.clone(), name.clone()), (target.clone(), mapped));
-        }
-    }
+            let p = reflect([0, 1, 2].map(|i| pts.iter().map(|p| p[i]).sum::<f64>() / k), point, n);
+            let face = match covers.get(&(body.to_string(), name.to_string())).map(Vec::as_slice) {
+                Some([only]) => Some(*only),
+                Some(several @ [_, _, ..]) => several
+                    .iter()
+                    .filter_map(|&g| tess.project_trimmed(g, p).map(|q| (dist(p, q), g)))
+                    .min_by(|a, b| a.0.total_cmp(&b.0))
+                    .map(|(_, g)| g),
+                _ => tess.nearest_face(p),
+            };
+            face.and_then(|i| names.get(i as usize)).cloned()
+        });
+        Some((target.clone(), mapped.unwrap_or_else(|| name.to_string())))
+    };
    let mut tags: BTreeMap<GeometryRef, u32> = BTreeMap::new();
    let mut tag = |model: &mut Model, r: GeometryRef| -> Result<u32> {
        if let Some(&t) = tags.get(&r) {
@@ -255,7 +274,7 @@ fn tag_image(
        }
        for (&f, &ft) in &t.faces {
            let Some(GeometryRef { body, entity: Entity::Face(name) }) = entity(ft) else { continue };
-            let Some((tb, tn)) = face_names.get(&(body, name)) else { continue };
+            let Some((tb, tn)) = image_face(e, f, &body, &name) else { continue };
            let g = faces.get(usize::from(f).saturating_sub(1)).copied().unwrap_or(f);
            let tg = tag(model, GeometryRef::face(tb.as_str(), tn.as_str())?)?;
            model.tag_element_face(copy, g, tg)?;
@@ -8,6 +8,7 @@ pub(crate) mod deck;
 pub(crate) mod define;
 pub mod diagnostics;
 mod edit;
+mod extrude;
 pub(crate) mod file;
 pub(crate) mod forms;
 mod geometry;
@@ -15,18 +16,29 @@ mod hex;
 pub(crate) mod mesh;

 pub use datum::edit_params as datum_edit_params;
+pub use datum::preview as datum_preview;
 pub use mesh::analytic_surfaces;
+pub use nodes::merge_preview as node_merge_preview;
+pub use plan::untagged_faces;
+pub use relax::{Preview as RelaxPreview, preview as relax_preview, sphere as relax_sphere};
 mod mirror;
 mod model;
+pub(crate) mod nodes;
 pub(crate) mod octree;
+pub(crate) mod plan;
+mod project;
+pub(crate) mod relax;
 pub mod replace;
 mod results;
 pub(crate) mod seeds;
 pub(crate) mod solve;
+pub(crate) mod stitch;
 mod symmetry;
 mod tags;
 pub mod update;
 pub(crate) mod view;
+mod virtual_faces;
+pub mod xy;

 use crate::schema::ProblemKind;
 use fieldcraft_model::MAX_LABEL;
@@ -41,6 +53,9 @@ pub static ALL: &[CommandSpec] = &[
    model::INFO,
    geometry::OPEN,
    geometry::BODIES,
+    geometry::FEATURES,
+    geometry::CENTRE,
+    geometry::CHECK,
    geometry::TESSELLATE,
    geometry::IMPORT_MESH,
    datum::DATUM_PLANE,
@@ -55,12 +70,24 @@ pub static ALL: &[CommandSpec] = &[
    view::ISOLATE,
    view::SHOW_ALL,
    datum::PARTITION,
+    datum::DATUM_SUPPRESS,
+    datum::PARTITION_SUPPRESS,
    datum::PARTITION_DELETE,
+    virtual_faces::FACES_MERGE,
+    virtual_faces::FACES_MERGE_DELETE,
+    virtual_faces::FACE_ABSORB,
+    virtual_faces::FACE_SPLIT,
+    virtual_faces::FACE_SPLIT_DELETE,
+    stitch::STITCH,
+    stitch::STITCH_DELETE,
    mesh::NODE_ADD,
    mesh::NODE_REMOVE,
    mesh::ELEMENT_ADD,
    mesh::ELEMENT_REMOVE,
+    replace::CLEAR,
    mesh::QUALITY,
+    mesh::QUALITY_MARK,
+    mesh::EXPORT_STL,
    mesh::DELAUNAY_POINTS,
    mesh::SURFACE_CHECK,
    mesh::PLANAR,
@@ -71,11 +98,20 @@ pub static ALL: &[CommandSpec] = &[
    hex::HEX_SWEEP,
    hex::HEX_MAPPED,
    hex::HEX_BLOCKS,
+    project::HEX_PROJECT,
+    extrude::HEX_EXTRUDE,
    cells::CELLS,
+    plan::PLAN,
+    plan::APPLY,
    seeds::SEED_EDGE,
    seeds::SEED_CLEAR,
    seeds::SEED_LIST,
    mirror::MIRROR,
+    nodes::MERGE,
+    nodes::DUPLICATES,
+    nodes::RENUMBER,
+    relax::RELAX,
+    relax::APPLY,
    tags::TAG,
    tags::TAG_CLEAR,
    model::UNITS,
@@ -106,6 +142,8 @@ pub static ALL: &[CommandSpec] = &[
    contact::TIE,
    contact::TIE_EDIT,
    contact::TIE_DELETE,
+    contact::RIGID_WALL,
+    contact::RIGID_WALL_DELETE,
    define::MASS_CREATE,
    define::MASS_EDIT,
    define::MASS_DELETE,
@@ -127,7 +165,9 @@ pub static ALL: &[CommandSpec] = &[
    define::STEP_EDIT,
    define::STEP_DELETE,
    define::STEP_ACTIVATE,
+    define::RENAME,
    define::ACTIVITY,
+    file::NEW,
    file::OPEN,
    file::SAVE,
    file::SAVE_AS,
@@ -154,9 +194,13 @@ pub static ALL: &[CommandSpec] = &[
    results::ANIMATE,
    results::FRAME,
    results::REACTIONS,
+    results::EXPORT_CSV,
+    results::EXPORT_VTU,
    results::CLEAR,
+    xy::XY,
    diagnostics::CRASH_REPORTS,
    diagnostics::CRASH_REPORT,
+    diagnostics::CRASH_REPORTS_DELETE,
    diagnostics::BUG_REPORT,
    diagnostics::CRASH_TEST,
    update::CHECK,
@@ -55,7 +55,21 @@ fn units(s: &mut Session, p: &Value) -> Result<Value> {
 }

 fn check(s: &mut Session, _: &Value) -> Result<Value> {
-    let diagnostics = s.model.check();
+    let mut diagnostics = s.model.check();
+    if let Some(design) = s.design.as_deref() {
+        for (body, n) in super::replace::stale(&s.model, design) {
+            diagnostics.push(fieldcraft_model::Diagnostic {
+                severity: Severity::Warning,
+                subject: format!("body `{body}`"),
+                message: format!(
+                    "{n} elements mesh a body the open design no longer has (its partitions changed since it was meshed); mesh.clear removes them"
+                ),
+            });
+        }
+    }
+    if let Some(why) = s.mesh_outdated() {
+        diagnostics.push(fieldcraft_model::Diagnostic { severity: Severity::Warning, subject: "mesh".into(), message: why });
+    }
    let errors = diagnostics.iter().filter(|d| d.severity == Severity::Error).count();
    let first_error = diagnostics.iter().find(|d| d.severity == Severity::Error).map(ToString::to_string);
    let progress = crate::progress::to_json(&s.progress_given(first_error));
@@ -0,0 +1,385 @@
+//! Node tools (#234): `mesh.node.merge` equivalences coincident nodes, `mesh.check.duplicates`
+//! finds what is not merged or does not join (coincident nodes, repeated elements, free faces and
+//! edges, cracks), and `mesh.renumber` gives nodes and elements new labels. Merging and
+//! renumbering move every reference with the labels (connectivity, sets, geometry tags, a step's
+//! displacement limit), so boundary conditions and loads, which act on sets, stay on the same
+//! entities; deck writers write the labels as they are. Both are one undo step; results solved
+//! before go stale, as after any mesh edit.
+
+use std::collections::{BTreeMap, BTreeSet};
+
+use fieldcraft_mesh::nodes::{Keep, bandwidth, duplicates, merge_plan, reverse_cuthill_mckee};
+use fieldcraft_model::geometry::Entity;
+use fieldcraft_model::{MAX_LABEL, Model};
+use serde_json::{Value, json};
+
+use crate::requirement::Requirement;
+use crate::schema::ProblemKind;
+use crate::{CommandKind, CommandSpec, EngineError, Result, Session};
+
+pub const MERGE: CommandSpec = CommandSpec {
+    id: "mesh.node.merge",
+    label: "Merge Nodes",
+    params: r#"{"tolerance"?: mm (default a millionth of the mesh's bounding-box diagonal), "set"?: "Name" (only the set's nodes and those of its elements and faces), "keep"?: "lowest" (default) | "highest"} — equivalences coincident nodes: every node within the distance of another becomes that one (the lowest or highest label of each group survives, keeping its position) in every element, set and geometry tag, and is removed. A merge that would put two nodes of one element together (collapsing it) is left out and listed under `refused`; the rest are made. Reports `merged`, the `pairs` [node, survivor] (the first 1000) and `refused`"#,
+    form: Some(super::forms::NODE_MERGE),
+    kind: CommandKind::Model,
+    requires: &[Requirement::Mesh],
+    run: merge,
+};
+
+pub const DUPLICATES: CommandSpec = CommandSpec {
+    id: "mesh.check.duplicates",
+    label: "Check Duplicates",
+    params: r#"{"tolerance"?: mm (default a millionth of the mesh's bounding-box diagonal)} — checks the mesh for what was not merged or does not join, changing nothing: `coincident` nodes within the distance of another ([node, other, distance]), `duplicate_elements` (groups on the same nodes), `free_faces` (faces of solid elements no other element shares: the skin), `cracks` (free faces lying on another free face: parts that touch without sharing nodes) and `free_edges` (edges of the skin and of 2D elements on one facet only: open borders). Lists hold the first 1000; `counts` has the totals"#,
+    form: Some(super::forms::CHECK_DUPLICATES),
+    kind: CommandKind::Model,
+    requires: &[Requirement::Mesh],
+    run: check_duplicates,
+};
+
+pub const RENUMBER: CommandSpec = CommandSpec {
+    id: "mesh.renumber",
+    label: "Renumber",
+    params: r#"{"what"?: "both" (default) | "nodes" | "elements", "by"?: "compact" (default: in label order) | "bandwidth" (nodes in reverse Cuthill–McKee order, elements by their lowest new node label) | "body" (body by body, by name; within a body in label order), "start"?: 1, "offset"?: n (instead of `by` and `start`: add n to every label)} — gives nodes and elements new labels from `start` up (or shifted by `offset`), every set, geometry tag and step following, so boundary conditions and loads stay on the same entities and decks write the new labels. Refused, changing nothing, when a label would leave 1..=99999999 or a node would take a reference point's label. Reports the counts renumbered, the label ranges and the bandwidth before and after"#,
+    form: Some(super::forms::RENUMBER),
+    kind: CommandKind::Model,
+    requires: &[Requirement::Mesh],
+    run: renumber,
+};
+
+/// Most items a reply lists.
+const MAX_LISTED: usize = 1000;
+
+/// The merge distance: `tolerance`, or a millionth of the mesh's bounding-box diagonal.
+pub(crate) fn tolerance(model: &Model, p: &Value) -> Result<f64> {
+    match p.get("tolerance") {
+        Some(v) => v.as_f64().filter(|t| *t > 0.0 && t.is_finite()).ok_or_else(|| EngineError::param("tolerance", ProblemKind::NotPositive)),
+        None => {
+            let (mut lo, mut hi) = ([f64::INFINITY; 3], [f64::NEG_INFINITY; 3]);
+            for n in model.nodes().values() {
+                for k in 0..3 {
+                    lo[k] = lo[k].min(n.xyz[k]);
+                    hi[k] = hi[k].max(n.xyz[k]);
+                }
+            }
+            let diagonal = (0..3).map(|k| (hi[k] - lo[k]).powi(2)).sum::<f64>().sqrt();
+            Ok(if diagonal > 0.0 && diagonal.is_finite() { 1e-6 * diagonal } else { 1e-9 })
+        }
+    }
+}
+
+/// The merge's candidates: the nodes of `set` (its own, and those of its elements and faces).
+fn candidates(model: &Model, p: &Value) -> Result<Option<BTreeSet<u32>>> {
+    let Some(name) = super::opt::<String>(p, "set")? else { return Ok(None) };
+    let set = model.resolve_set(&name)?;
+    let mut nodes: BTreeSet<u32> = set.nodes.into_iter().collect();
+    for e in set.elements.iter().chain(set.faces.iter().map(|f| &f.element)) {
+        if let Some(el) = model.element(*e) {
+            nodes.extend(el.nodes.iter().copied());
+        }
+    }
+    Ok(Some(nodes))
+}
+
+fn keep(p: &Value) -> Result<Keep> {
+    match super::opt::<String>(p, "keep")?.as_deref() {
+        None | Some("lowest") => Ok(Keep::Lowest),
+        Some("highest") => Ok(Keep::Highest),
+        Some(_) => Err(EngineError::param("keep", ProblemKind::NotAChoice)),
+    }
+}
+
+/// The merges `mesh.node.merge` with `params` would make, as [node, survivor] pairs: what its
+/// form previews. `None` when the parameters are not (yet) valid.
+pub fn merge_preview(s: &Session, params: &Value) -> Option<Vec<[u32; 2]>> {
+    let tol = tolerance(&s.model, params).ok()?;
+    let only = candidates(&s.model, params).ok()?;
+    let plan = merge_plan(&s.model, only.as_ref(), tol, keep(params).ok()?).ok()?;
+    Some(plan.map.into_iter().map(|(a, b)| [a, b]).collect())
+}
+
+fn merge(s: &mut Session, p: &Value) -> Result<Value> {
+    let tol = tolerance(&s.model, p)?;
+    let only = candidates(&s.model, p)?;
+    let plan = merge_plan(&s.model, only.as_ref(), tol, keep(p)?)?;
+    if !plan.map.is_empty() {
+        s.model.merge_nodes(&plan.map)?;
+    }
+    let pairs: Vec<[u32; 2]> = plan.map.iter().take(MAX_LISTED).map(|(&a, &b)| [a, b]).collect();
+    let refused: Vec<Value> =
+        plan.refused.iter().take(MAX_LISTED).map(|r| json!({"node": r.node, "survivor": r.survivor, "element": r.element})).collect();
+    let mut summary = format!("merged {} node{} within {tol:.3e}", plan.map.len(), if plan.map.len() == 1 { "" } else { "s" });
+    if !plan.refused.is_empty() {
+        summary.push_str(&format!("; {} left apart (they would collapse an element)", plan.refused.len()));
+    }
+    Ok(json!({
+        "merged": plan.map.len(),
+        "pairs": pairs,
+        "refused": refused,
+        "tolerance": tol,
+        "nodes": s.model.nodes().len(),
+        "summary": summary,
+    }))
+}
+
+fn check_duplicates(s: &mut Session, p: &Value) -> Result<Value> {
+    let tol = tolerance(&s.model, p)?;
+    let d = duplicates(&s.model, tol)?;
+    let coincident: Vec<Value> = d.coincident.iter().take(MAX_LISTED).map(|&(a, b, dist)| json!([a, b, dist])).collect();
+    let summary = format!(
+        "{} coincident node{}, {} duplicate element group{}, {} crack face{}, {} free edge{} ({} free faces)",
+        d.coincident.len(),
+        plural(d.coincident.len()),
+        d.elements.len(),
+        plural(d.elements.len()),
+        d.cracks.len(),
+        plural(d.cracks.len()),
+        d.free_edges.len(),
+        plural(d.free_edges.len()),
+        d.free_faces,
+    );
+    Ok(json!({
+        "tolerance": tol,
+        "coincident": coincident,
+        "duplicate_elements": d.elements.iter().take(MAX_LISTED).collect::<Vec<_>>(),
+        "free_faces": d.free_faces,
+        "cracks": d.cracks.iter().take(MAX_LISTED).collect::<Vec<_>>(),
+        "free_edges": d.free_edges.iter().take(MAX_LISTED).collect::<Vec<_>>(),
+        "counts": {
+            "coincident": d.coincident.len(),
+            "duplicate_elements": d.elements.len(),
+            "cracks": d.cracks.len(),
+            "free_edges": d.free_edges.len(),
+        },
+        "summary": summary,
+    }))
+}
+
+fn plural(n: usize) -> &'static str {
+    if n == 1 { "" } else { "s" }
+}
+
+/// The body name of each element tagged with one.
+fn element_bodies(model: &Model) -> BTreeMap<u32, String> {
+    let c = model.classification();
+    c.elements()
+        .iter()
+        .filter_map(|(&e, t)| {
+            let r = c.entity(t.region?)?;
+            (r.entity == Entity::Body).then(|| (e, r.body.clone()))
+        })
+        .collect()
+}
+
+/// New labels for `order` from `start` up; `None` when they would leave the label range.
+fn from_start(order: &[u32], start: u32) -> Option<BTreeMap<u32, u32>> {
+    order
+        .iter()
+        .enumerate()
+        .map(|(i, &l)| Some((l, start.checked_add(u32::try_from(i).ok()?).filter(|x| *x <= MAX_LABEL)?)))
+        .filter(|x| x.as_ref().is_none_or(|(a, b)| a != b))
+        .collect()
+}
+
+fn renumber(s: &mut Session, p: &Value) -> Result<Value> {
+    let (nodes_too, elements_too) = match super::opt::<String>(p, "what")?.as_deref() {
+        None | Some("both") => (true, true),
+        Some("nodes") => (true, false),
+        Some("elements") => (false, true),
+        Some(_) => return Err(EngineError::param("what", ProblemKind::NotAChoice)),
+    };
+    let model = &s.model;
+    let out_of_range = || EngineError::Params(format!("the new labels would leave 1..={MAX_LABEL}"));
+    let (node_map, element_map) = if let Some(v) = p.get("offset") {
+        if p.get("by").is_some() || p.get("start").is_some() {
+            return Err(EngineError::Params("give `offset`, or `by` and `start`, not both".into()));
+        }
+        let offset = v
+            .as_i64()
+            .ok_or_else(|| EngineError::param("offset", ProblemKind::NotAWholeNumber { min: -i64::from(MAX_LABEL), max: i64::from(MAX_LABEL) }))?;
+        let shift = |labels: &mut dyn Iterator<Item = u32>| -> Result<BTreeMap<u32, u32>> {
+            labels
+                .filter(|_| offset != 0)
+                .map(|l| u32::try_from(i64::from(l) + offset).ok().filter(|x| (1..=MAX_LABEL).contains(x)).map(|n| (l, n)).ok_or_else(out_of_range))
+                .collect()
+        };
+        let n = if nodes_too { shift(&mut model.nodes().keys().copied())? } else { BTreeMap::new() };
+        let e = if elements_too { shift(&mut model.elements().keys().copied())? } else { BTreeMap::new() };
+        (n, e)
+    } else {
+        let start = match p.get("start") {
+            None => 1,
+            Some(v) => v
+                .as_u64()
+                .and_then(|x| u32::try_from(x).ok())
+                .filter(|x| (1..=MAX_LABEL).contains(x))
+                .ok_or_else(|| EngineError::param("start", ProblemKind::NotAWholeNumber { min: 1, max: i64::from(MAX_LABEL) }))?,
+        };
+        let (node_order, element_order): (Vec<u32>, Vec<u32>) = match super::opt::<String>(p, "by")?.as_deref() {
+            None | Some("compact") => (model.nodes().keys().copied().collect(), model.elements().keys().copied().collect()),
+            Some("bandwidth") => {
+                let nodes = reverse_cuthill_mckee(model);
+                let rank: BTreeMap<u32, usize> = nodes.iter().enumerate().map(|(i, &l)| (l, i)).collect();
+                let mut elements: Vec<(usize, u32)> = model
+                    .elements()
+                    .iter()
+                    .map(|(&l, e)| (e.nodes.iter().filter_map(|n| rank.get(n).copied()).min().unwrap_or(usize::MAX), l))
+                    .collect();
+                elements.sort_unstable();
+                (nodes, elements.into_iter().map(|(_, l)| l).collect())
+            }
+            Some("body") => {
+                let bodies = element_bodies(model);
+                // Elements by body name (untagged last), then label; nodes as their first
+                // element in that order meets them, then the nodes no element uses.
+                let mut elements: Vec<(Option<&String>, u32)> = model.elements().keys().map(|&l| (bodies.get(&l), l)).collect();
+                elements.sort_by(|a, b| (a.0.is_none(), a.0, a.1).cmp(&(b.0.is_none(), b.0, b.1)));
+                let elements: Vec<u32> = elements.into_iter().map(|(_, l)| l).collect();
+                let mut seen = BTreeSet::new();
+                let mut nodes: Vec<u32> = Vec::with_capacity(model.nodes().len());
+                for e in &elements {
+                    for &n in model.element(*e).map(|x| x.nodes.as_slice()).unwrap_or(&[]) {
+                        if seen.insert(n) {
+                            nodes.push(n);
+                        }
+                    }
+                }
+                let mut free: Vec<u32> = model.nodes().keys().copied().filter(|n| !seen.contains(n)).collect();
+                free.sort_unstable();
+                nodes.extend(free);
+                (nodes, elements)
+            }
+            Some(_) => return Err(EngineError::param("by", ProblemKind::NotAChoice)),
+        };
+        let n = if nodes_too { from_start(&node_order, start).ok_or_else(out_of_range)? } else { BTreeMap::new() };
+        let e = if elements_too { from_start(&element_order, start).ok_or_else(out_of_range)? } else { BTreeMap::new() };
+        (n, e)
+    };
+    let before = bandwidth(model, &|l| l);
+    s.model.renumber(&node_map, &element_map)?;
+    let after = bandwidth(&s.model, &|l| l);
+    let range = |labels: &mut dyn Iterator<Item = u32>| -> Value {
+        let (lo, hi) = labels.fold((u32::MAX, 0), |(lo, hi), l| (lo.min(l), hi.max(l)));
+        if hi == 0 { Value::Null } else { json!([lo, hi]) }
+    };
+    Ok(json!({
+        "nodes": node_map.len(),
+        "elements": element_map.len(),
+        "node_labels": range(&mut s.model.nodes().keys().copied()),
+        "element_labels": range(&mut s.model.elements().keys().copied()),
+        "bandwidth": [before, after],
+        "summary": format!("renumbered {} nodes and {} elements; bandwidth {before} → {after}", node_map.len(), element_map.len()),
+    }))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// A 2 × 1 × 1 bar of hex8 blocks: whole, or as two halves that do not share their nodes
+    /// on x = 1.
+    fn bar(halves: bool) -> Session {
+        let mut s = Session::default();
+        let block = |body: &str, x0: f64, x1: f64, n: u32| {
+            let c = [[x0, 0., 0.], [x1, 0., 0.], [x1, 1., 0.], [x0, 1., 0.], [x0, 0., 1.], [x1, 0., 1.], [x1, 1., 1.], [x0, 1., 1.]];
+            json!({"body": body, "kind": "hex8", "corners": c, "divisions": [n, 2, 2], "merge": 0})
+        };
+        if halves {
+            s.execute("mesh.block", &block("A", 0.0, 1.0, 2)).unwrap();
+            s.execute("mesh.block", &block("B", 1.0, 2.0, 2)).unwrap();
+        } else {
+            s.execute("mesh.block", &block("A", 0.0, 2.0, 4)).unwrap();
+        }
+        s
+    }
+
+    fn positions(s: &Session) -> Vec<[u64; 3]> {
+        let mut p: Vec<[u64; 3]> = s.model.nodes().values().map(|n| n.xyz.map(|x| (x + 0.0).to_bits())).collect();
+        p.sort_unstable();
+        p
+    }
+
+    /// Two halves meshed apart are found coincident and cracked, and merging them gives the
+    /// whole bar's nodes: no crack left, and undo brings the halves back.
+    #[test]
+    fn merging_two_halves_gives_the_whole() {
+        let whole = bar(false);
+        let mut s = bar(true);
+        s.execute(
+            "model.set.create",
+            &json!({"name": "seam", "nodes": s.model.nodes().iter().filter(|(_, n)| n.xyz[0] == 1.0).map(|(l, _)| *l).collect::<Vec<_>>()}),
+        )
+        .unwrap();
+        let d = s.execute("mesh.check.duplicates", &json!({})).unwrap();
+        assert_eq!(d["counts"]["coincident"], 9, "{d}");
+        assert_eq!(d["counts"]["cracks"], 8, "{d}");
+        assert_eq!(d["counts"]["free_edges"], 0, "{d}");
+        assert_eq!(s.model.nodes().len(), whole.model.nodes().len() + 9);
+
+        let r = s.execute("mesh.node.merge", &json!({})).unwrap();
+        assert_eq!(r["merged"], 9, "{r}");
+        assert_eq!(positions(&s), positions(&whole));
+        // The seam set keeps its nine positions, on the survivors.
+        assert_eq!(s.model.set("seam").unwrap().nodes.len(), 9);
+        let d = s.execute("mesh.check.duplicates", &json!({})).unwrap();
+        assert_eq!((d["counts"]["coincident"].as_u64(), d["counts"]["cracks"].as_u64()), (Some(0), Some(0)), "{d}");
+        s.execute("edit.undo", &json!({})).unwrap();
+        assert_eq!(s.model.nodes().len(), whole.model.nodes().len() + 9);
+
+        // Keeping the highest labels; only a set's nodes; hostile parameters change nothing.
+        let r = s.execute("mesh.node.merge", &json!({"keep": "highest", "set": "seam"})).unwrap();
+        assert!(r["pairs"].as_array().unwrap().iter().all(|p| p[0].as_u64() < p[1].as_u64()), "{r}");
+        s.execute("edit.undo", &json!({})).unwrap();
+        for bad in [json!({"tolerance": -1}), json!({"tolerance": "x"}), json!({"keep": "middle"}), json!({"set": "nope"})] {
+            assert!(s.execute("mesh.node.merge", &bad).is_err(), "{bad}");
+        }
+        assert!(merge_preview(&s, &json!({})).is_some_and(|p| p.len() == 9));
+    }
+
+    /// Renumbering keeps the analysis: the cantilever solves to the same displacements, point
+    /// for point, after its nodes take the bandwidth order from 1000 and its elements are
+    /// shifted; the deck writes the new labels.
+    #[test]
+    fn renumbering_keeps_the_solution() {
+        let mut s = Session::default();
+        s.run_script(&crate::sample::cantilever()).unwrap();
+        let at = json!([[100.0, 10.0, 10.0], [50.0, 0.0, 20.0], [25.0, 20.0, 0.0]]);
+        let probe = |s: &mut Session| {
+            s.execute("solve.static", &json!({})).unwrap();
+            s.execute("solve.probe", &json!({"step": "Load", "at": at})).unwrap()["nodes"].clone()
+        };
+        let before = probe(&mut s);
+        let bw = bandwidth(&s.model, &|l| l);
+        let r = s.execute("mesh.renumber", &json!({"what": "nodes", "by": "bandwidth", "start": 1000})).unwrap();
+        assert_eq!(r["node_labels"][0], 1000, "{r}");
+        assert!(r["bandwidth"][1].as_u64().unwrap() <= u64::from(bw), "{r}");
+        s.execute("mesh.renumber", &json!({"what": "elements", "offset": 500})).unwrap();
+        assert_eq!(s.model.elements().keys().next().copied(), Some(501));
+        let after = probe(&mut s);
+        for (a, b) in before.as_array().unwrap().iter().zip(after.as_array().unwrap()) {
+            for k in 0..3 {
+                let (x, y) = (a["displacement"][k].as_f64().unwrap(), b["displacement"][k].as_f64().unwrap());
+                // Equal to roundoff of the tip deflection (0.24 mm).
+                assert!((x - y).abs() <= 1e-9, "{a} vs {b}");
+            }
+        }
+        let deck = fieldcraft_decks::abaqus::write(&s.model).unwrap();
+        assert!(deck.lines().any(|l| l.starts_with("1000,")) && deck.lines().any(|l| l.starts_with("501,")), "{deck}");
+        // Body by body and compact, then refusals that change nothing.
+        s.execute("mesh.renumber", &json!({"by": "body"})).unwrap();
+        s.execute("mesh.renumber", &json!({})).unwrap();
+        assert_eq!(s.model.nodes().keys().next().copied(), Some(1));
+        let model = s.model.clone();
+        for bad in [
+            json!({"offset": -1}),
+            json!({"start": 99_999_999}),
+            json!({"start": 0}),
+            json!({"by": "random"}),
+            json!({"what": "faces"}),
+            json!({"offset": 1, "start": 3}),
+        ] {
+            assert!(s.execute("mesh.renumber", &bad).is_err(), "{bad}");
+        }
+        assert_eq!(s.model, model);
+    }
+}
@@ -60,7 +60,7 @@ fn hex_octree(s: &mut Session, p: &Value) -> Result<Value> {
        let surface = BoundarySurface::new(&b.mesh.positions, &b.mesh.triangles, &b.mesh.tri_face, &surface_options)
            .map_err(|e| EngineError::Params(format!("body `{}`: {e}", b.name)))?;
        let left = OctreeOptions { max_elements: options.max_elements.saturating_sub(total).max(1), ..options.clone() };
-        let mesh = octree_hex_mesh(&surface, &UniformSize(h), &left).map_err(|e| EngineError::Params(format!("body `{}`: {e}", b.name)))?;
+        let mesh = octree_hex_mesh(&surface, &UniformSize(h), &left).map_err(|e| EngineError::of_body(&b.name, e))?;
        total += mesh.hexes.len();
        meshes.push((b, mesh));
    }
@@ -0,0 +1,832 @@
+//! The plan's block topology for the projection blocking mesher (#402 step 3, #399): the
+//! translation of a mesh plan into one block topology over the whole body, so the rings round
+//! its circles and the blend layer along its fillets, chamfers and shell walls come out of one
+//! conforming mesh (no partitions, no ties, one division count per sheet of blocks).
+//!
+//! The body is read in a frame whose third axis is the plan's sweep direction (a principal axis):
+//! - **Grid.** The planes of the body's planar faces square to each axis (its sides, a shell's
+//!   inner walls and floor, a boss's top, a blind hole's bottom) and the frames round its
+//!   circles make a grid of blocks over the body.
+//! - **Rings.** The frame cell round each circle (concentric circles together) is O-gridded
+//!   through every level, square inside square: the frame, then a square with its corners at
+//!   45° on each circle, then a core. Corners on a circle sit on it before projection, so the
+//!   ring's radial block edges meet the cylinder square on. A hole's frame is centred on it: a
+//!   side of the body near the hole is the frame there and the far side is as far; a fillet
+//!   round a corner of the outline that holds a hole (a screw hole in a rounded corner) is taken
+//!   in by the hole's ring, its frame reaching the two sides and its outer corner projected onto
+//!   the fillet's middle, so the corner needs no blend layer. A boss the body's walls run into
+//!   (planes of the body crossing its circle outside it) is framed by the square round its
+//!   whole circle, subdivided by those planes, every square inside it divided alike so the
+//!   ring's blocks meet the walls node to node; on the walls' side the frame stops at their
+//!   inner plane and its corner projects onto the inner fillet's middle (a boss just touching
+//!   the fillet included).
+//! - **Blend layer.** A side of the body a fillet or chamfer runs along, or that a shell's wall
+//!   stands on, gets a layer of blocks between the grid (on the body shrunk by the blend's
+//!   depth or the wall's thickness) and the side, one block per boundary face of the grid, the
+//!   layer's vertices pushed out square to every side they lie on: diagonally at an edge and a
+//!   corner. Projected, a corner vertex lands on the fillet (or chamfer) at its middle, so the
+//!   two blocks meeting there share the blend's 180° as two right angles; on a shell's inner
+//!   corner, as three 120°-ish ones. The layer's depth is the blend's measured depth (its
+//!   stored radius or distance) or the wall's thickness; its divisions follow the element size.
+//! - **Carving.** Every block whose middle lies outside the body (a cavity, the space round a
+//!   boss, a hole's core) is removed, by the generalized winding number of the body's
+//!   tessellation (solid angles, Van Oosterom and Strackee 1983).
+//!
+//! The projection mesher then projects the outer block faces onto the body's faces (each the
+//! smooth group nearest it) and smooths the grid. Parallel block edges share one division count
+//! across the whole topology, so neighbouring blocks always match: no shear bands, no ties.
+//!
+//! A body this layout does not fit (a face at an angle to the axes that is not a chamfer, a
+//! curved face that is neither a circle's cylinder nor a blend, two circles in one frame) is
+//! reported with the reason; the plan then keeps its frame cuts and swept cells.
+
+use fieldcraft_geometry::{FaceSurface, Shape, SurfaceMesh};
+use fieldcraft_mesh::project::Topology;
+use fieldcraft_model::{PlanRing, RingKind};
+
+type V3 = [f64; 3];
+
+/// Most blocks a plan's layout makes before carving.
+const MAX_LAYOUT_BLOCKS: usize = 20_000;
+/// Most triangles the winding number classification sums over per point.
+const MAX_CLASSIFY_TRIANGLES: usize = 400_000;
+
+/// A body's block layout.
+#[derive(Debug, Clone)]
+pub(crate) struct Layout {
+    pub(crate) topology: Topology,
+    /// Circles ringed (concentric ones each).
+    pub(crate) rings: usize,
+    /// The sides with a blend layer: (side, depth, what).
+    pub(crate) layers: Vec<(String, f64, &'static str)>,
+    /// Grid planes per axis of the frame (across, across, along the sweep).
+    pub(crate) planes: [usize; 3],
+    /// The frame round each circle group: its axis point (the sweep's coordinate 0) and the
+    /// smallest half-side of the frame.
+    pub(crate) frames: Vec<(V3, f64)>,
+    /// The ring-and-pillow layout ([`super::pillow`]): the pillow's least thickness along the walls.
+    pub(crate) pillow: Option<f64>,
+}
+
+impl Layout {
+    /// The half-side of the frame round the circle about the axis through `center` along the
+    /// sweep `direction`.
+    pub(crate) fn frame_of(&self, center: V3, direction: V3) -> Option<f64> {
+        self.frames.iter().find_map(|(p, half)| {
+            let off = sub(center, *p);
+            let along = dot(off, direction);
+            (dot(off, off) - along * along < 1e-12 * dot(center, center).max(1.0)).then_some(*half)
+        })
+    }
+
+    pub(crate) fn summary(&self) -> String {
+        let layers: Vec<String> = self.layers.iter().map(|(s, d, w)| format!("{s} {d:.4} mm ({w})")).collect();
+        format!(
+            "projection blocking: {} blocks over a {}×{}×{} grid, {} circle(s) ringed{}{}",
+            self.topology.blocks.len(),
+            self.planes[0].saturating_sub(1),
+            self.planes[1].saturating_sub(1),
+            self.planes[2].saturating_sub(1),
+            self.rings,
+            if layers.is_empty() { String::new() } else { format!(", a blend layer on {}", layers.join(", ")) },
+            self.pillow.map_or_else(String::new, |t| format!(", a pillow layer from the carved grid to the walls ({t:.4} mm and more)"))
+        )
+    }
+}
+
+/// What the layout reads.
+pub(crate) struct Input<'a> {
+    pub(crate) shape: &'a Shape,
+    pub(crate) surfaces: &'a [Option<FaceSurface>],
+    pub(crate) mesh: &'a SurfaceMesh,
+    pub(crate) direction: V3,
+    pub(crate) rings: &'a [PlanRing],
+    /// The faces fillets and chamfers made (indices on `shape`).
+    pub(crate) blends: Vec<u32>,
+    /// A shell's wall thickness.
+    pub(crate) shell: Option<f64>,
+    pub(crate) size: f64,
+}
+
+/// The local frame: local axis `a` is world axis `PERM[k][a]`, `k` the sweep's world axis (a
+/// cyclic permutation, so blocks keep their handedness).
+pub(super) const PERM: [[usize; 3]; 3] = [[1, 2, 0], [2, 0, 1], [0, 1, 2]];
+
+const SIDE_NAMES: [[&str; 2]; 3] = [["-x", "+x"], ["-y", "+y"], ["-z", "+z"]];
+
+fn dot(a: V3, b: V3) -> f64 {
+    a[0] * b[0] + a[1] * b[1] + a[2] * b[2]
+}
+
+fn sub(a: V3, b: V3) -> V3 {
+    [a[0] - b[0], a[1] - b[1], a[2] - b[2]]
+}
+
+fn norm(a: V3) -> f64 {
+    dot(a, a).sqrt()
+}
+
+fn cross(a: V3, b: V3) -> V3 {
+    [a[1] * b[2] - a[2] * b[1], a[2] * b[0] - a[0] * b[2], a[0] * b[1] - a[1] * b[0]]
+}
+
+/// Twice the solid angle triangle `a b c` subtends at the origin, signed (Van Oosterom and
+/// Strackee 1983: tan(Ω/2) = a·(b×c) / (|a||b||c| + (a·b)|c| + (a·c)|b| + (b·c)|a|)).
+fn solid_angle(a: V3, b: V3, c: V3) -> f64 {
+    let (la, lb, lc) = (norm(a), norm(b), norm(c));
+    let num = dot(a, cross(b, c));
+    let den = la * lb * lc + dot(a, b) * lc + dot(a, c) * lb + dot(b, c) * la;
+    2.0 * num.atan2(den)
+}
+
+/// The generalized winding number of the closed surface `mesh` at `p`: 1 inside, 0 outside.
+pub(super) fn winding(mesh: &SurfaceMesh, p: V3) -> f64 {
+    let at = |i: u32| mesh.positions.get(i as usize).map(|q| sub(*q, p));
+    let mut sum = 0.0;
+    for t in mesh.triangles.iter().take(MAX_CLASSIFY_TRIANGLES) {
+        if let (Some(a), Some(b), Some(c)) = (at(t[0]), at(t[1]), at(t[2])) {
+            sum += solid_angle(a, b, c);
+        }
+    }
+    sum / (4.0 * std::f64::consts::PI)
+}
+
+/// A circle's axis point and radius in the local frame, with its kind.
+#[derive(Debug, Clone, Copy)]
+struct Circle {
+    c: [f64; 2],
+    r: f64,
+    kind: RingKind,
+}
+
+/// Concentric circles framed together: radii descending.
+#[derive(Debug, Clone)]
+struct Group {
+    c: [f64; 2],
+    circles: Vec<Circle>,
+    /// The frame's extent per local axis (0, 1): [low, high].
+    frame: [[f64; 2]; 2],
+    /// The frame's half-side per local axis when a corner blend it takes in sets it: the
+    /// distance from the centre to the body's side the blend runs along.
+    forced: [Option<f64>; 2],
+    /// A boss the body's walls run into: planes of the body cross its circle (outside it, where
+    /// the walls join), so its frame is the square round the whole circle, subdivided by those
+    /// planes, and the ring's blocks follow the subdivision.
+    patch: bool,
+    /// The extent per local axis of the concave blends a patch takes in (the inner fillet where
+    /// the walls meet, in pieces where the boss touches it): the frame's side on the blends'
+    /// side of the centre goes to their middle.
+    blends: Option<[[f64; 2]; 2]>,
+}
+
+/// Plan the block topology of the body.
+// Axes index several per-axis arrays at once (planes, frames, layers).
+#[allow(clippy::needless_range_loop)]
+pub(crate) fn layout(inp: &Input) -> Result<Layout, String> {
+    let d = inp.direction;
+    let k = (0..3).find(|&k| (d[k].abs() - 1.0).abs() < 1e-9).ok_or("the sweep direction is not along an axis")?;
+    let perm = PERM[k];
+    let local = |p: V3| -> V3 { [p[perm[0]], p[perm[1]], p[perm[2]]] };
+    let world = |l: V3| -> V3 {
+        let mut w = [0.0; 3];
+        for a in 0..3 {
+            w[perm[a]] = l[a];
+        }
+        w
+    };
+    if inp.mesh.triangles.is_empty() || inp.mesh.triangles.len() > MAX_CLASSIFY_TRIANGLES {
+        return Err(format!("the body's tessellation has {} triangles", inp.mesh.triangles.len()));
+    }
+    let (mut lo, mut hi) = ([f64::INFINITY; 3], [f64::NEG_INFINITY; 3]);
+    let mut face_points: Vec<Vec<V3>> = vec![Vec::new(); inp.surfaces.len()];
+    for (t, &f) in inp.mesh.triangles.iter().zip(&inp.mesh.tri_face) {
+        for &i in t {
+            let Some(p) = inp.mesh.positions.get(i as usize).map(|p| local(*p)) else { continue };
+            for a in 0..3 {
+                lo[a] = lo[a].min(p[a]);
+                hi[a] = hi[a].max(p[a]);
+            }
+            if let Some(list) = face_points.get_mut(f as usize) {
+                list.push(p);
+            }
+        }
+    }
+    let diag = norm(sub(hi, lo));
+    if !(diag.is_finite() && diag > 0.0) {
+        return Err("the body has no extent".into());
+    }
+    let eps = 1e-6 * diag;
+    let name = |f: usize| inp.shape.faces().get(f).map_or_else(|| format!("#{f}"), |x| x.name.clone());
+
+    // Circles: the plan's rings along the sweep, in the local frame.
+    let mut circles: Vec<Circle> = Vec::new();
+    for r in inp.rings {
+        if (dot(r.axis, d).abs() - 1.0).abs() > 1e-6 {
+            return Err(format!("the ring of F{} is not square to the sweep", r.feature));
+        }
+        let c = local(r.center);
+        circles.push(Circle { c: [c[0], c[1]], r: r.radius, kind: r.kind });
+    }
+    let on_circle = |origin: V3, radius: f64| {
+        let o = local(origin);
+        circles.iter().any(|c| (c.r - radius).abs() < 1e-6 * radius.max(1.0) && (c.c[0] - o[0]).hypot(c.c[1] - o[1]) < 1e-6 * radius.max(1.0))
+    };
+
+    // The faces: planes square to an axis (with their outward sign), the circles' cylinders, and
+    // the blends; anything else is not this layout's.
+    let mut planes_on: [Vec<(f64, f64)>; 3] = [Vec::new(), Vec::new(), Vec::new()];
+    // The planar faces square to an in-plane axis: (axis, offset, face).
+    let mut side_faces: Vec<(usize, f64, usize)> = Vec::new();
+    let mut blend_faces: Vec<usize> = Vec::new();
+    for (f, s) in inp.surfaces.iter().enumerate() {
+        let blend = inp.blends.contains(&(f as u32));
+        match s {
+            Some(FaceSurface::Plane { normal, point }) => {
+                let n = local(*normal);
+                match (0..3).find(|&a| (n[a].abs() - 1.0).abs() < 1e-6) {
+                    Some(a) => {
+                        planes_on[a].push((local(*point)[a], n[a].signum()));
+                        if a < 2 {
+                            side_faces.push((a, local(*point)[a], f));
+                        }
+                    }
+                    None if blend => blend_faces.push(f),
+                    None => return Err(format!("face `{}` is a plane at an angle to the axes", name(f))),
+                }
+            }
+            // A ring's cylinder, even where a fillet's history names it (a boss over a filleted
+            // corner).
+            Some(FaceSurface::Cylinder { origin, axis, radius }) if (dot(*axis, d).abs() - 1.0).abs() < 1e-6 && on_circle(*origin, *radius) => {}
+            Some(FaceSurface::Cylinder { .. }) if !blend => {
+                return Err(format!("face `{}` is a cylinder that is not one of the plan's rings", name(f)));
+            }
+            _ if blend => blend_faces.push(f),
+            _ => return Err(format!("face `{}` is curved and neither a ring's cylinder nor a fillet's", name(f))),
+        }
+    }
+
+    // Circles, concentric ones grouped (radii descending).
+    let mut groups: Vec<Group> = Vec::new();
+    for c in &circles {
+        match groups.iter_mut().find(|g| (g.c[0] - c.c[0]).hypot(g.c[1] - c.c[1]) < 1e-6 * c.r.max(1.0)) {
+            Some(g) => {
+                if !g.circles.iter().any(|x| (x.r - c.r).abs() < 1e-6 * c.r.max(1.0)) {
+                    g.circles.push(*c);
+                }
+            }
+            None => groups.push(Group { c: c.c, circles: vec![*c], frame: [[0.0; 2]; 2], forced: [None; 2], patch: false, blends: None }),
+        }
+    }
+    for g in &mut groups {
+        g.circles.sort_by(|a, b| b.r.total_cmp(&a.r));
+        let Some(outer) = g.circles.first().copied() else { continue };
+        let r0 = outer.r;
+        let crossing: Vec<usize> = side_faces.iter().filter(|(a, v, _)| (v - g.c[*a]).abs() < r0 - eps).map(|(_, _, f)| *f).collect();
+        if outer.kind != RingKind::Butterfly || crossing.is_empty() {
+            continue;
+        }
+        // The walls join the boss outside its circle: no face of theirs inside it.
+        for f in crossing {
+            let pts = face_points.get(f).map_or(&[][..], Vec::as_slice);
+            if pts.iter().any(|p| (p[0] - g.c[0]).hypot(p[1] - g.c[1]) < r0 * (1.0 - 1e-3)) {
+                return Err(format!("face `{}` runs through the circle of radius {r0:.4}", name(f)));
+            }
+        }
+        g.patch = true;
+    }
+
+    // The blend layer: per side, the depth of the blends along it, or the shell's wall. A blend
+    // round a corner of the outline that a hole's ring can frame (a screw hole in a rounded
+    // corner) is taken in by the ring instead.
+    let mut ring = [[0.0f64; 2]; 3];
+    let mut what = [[""; 2]; 3];
+    for &f in &blend_faces {
+        let pts = face_points.get(f).map_or(&[][..], Vec::as_slice);
+        if pts.is_empty() {
+            continue;
+        }
+        if let Some((g, half)) = corner_ring(&groups, pts, lo, hi, eps)
+            && let Some(g) = groups.get_mut(g)
+        {
+            g.forced = half.map(Some);
+            continue;
+        }
+        if let Some((g, extent)) = patch_blend(&groups, pts)
+            && let Some(g) = groups.get_mut(g)
+        {
+            let union = g.blends.map_or(extent, |b| std::array::from_fn(|a| [b[a][0].min(extent[a][0]), b[a][1].max(extent[a][1])]));
+            g.blends = Some(union);
+            continue;
+        }
+        let mut touched = false;
+        for a in 0..3 {
+            for s in 0..2 {
+                let depth = pts.iter().map(|p| if s == 0 { p[a] - lo[a] } else { hi[a] - p[a] }).fold(0.0f64, f64::max);
+                if depth < 0.45 * (hi[a] - lo[a]) {
+                    touched = true;
+                    if depth > ring[a][s] {
+                        ring[a][s] = depth;
+                        what[a][s] = "blend";
+                    }
+                }
+            }
+        }
+        if !touched {
+            return Err(format!("the blend face `{}` does not run along a side of the body", name(f)));
+        }
+    }
+    if let Some(t) = inp.shell.filter(|t| t.is_finite() && *t > 0.0) {
+        // A wall: the inner face of the shell, `t` inside the side and facing away from it.
+        for a in 0..3 {
+            for s in 0..2 {
+                let at = if s == 0 { lo[a] + t } else { hi[a] - t };
+                let inward = if s == 0 { 1.0 } else { -1.0 };
+                if planes_on[a].iter().any(|(v, sign)| (v - at).abs() < 1e-4 * t.max(1.0) && *sign == inward) {
+                    ring[a][s] = t;
+                    what[a][s] = "shell wall";
+                }
+            }
+        }
+    }
+    let ilo: V3 = std::array::from_fn(|a| lo[a] + ring[a][0]);
+    let ihi: V3 = std::array::from_fn(|a| hi[a] - ring[a][1]);
+    if (0..3).any(|a| !(ihi[a] - ilo[a] > eps)) {
+        return Err("the blend layers leave no room inside the body".into());
+    }
+
+    // The fixed planes per axis: faces square to it (a side with a layer moves in by its depth).
+    let mut fixed: [Vec<f64>; 3] = [Vec::new(), Vec::new(), Vec::new()];
+    for a in 0..3 {
+        for &(v, _) in &planes_on[a] {
+            let v = if ring[a][0] > 0.0 && (v - lo[a]).abs() < eps {
+                ilo[a]
+            } else if ring[a][1] > 0.0 && (v - hi[a]).abs() < eps {
+                ihi[a]
+            } else {
+                v
+            };
+            if v < ilo[a] - eps || v > ihi[a] + eps {
+                return Err(format!("a face square to {} lies inside the blend layer", SIDE_NAMES[perm[a]][0].trim_start_matches('-')));
+            }
+            fixed[a].push(v);
+        }
+        if ring[a][0] > 0.0 {
+            fixed[a].push(ilo[a]);
+        }
+        if ring[a][1] > 0.0 {
+            fixed[a].push(ihi[a]);
+        }
+        fixed[a].sort_by(f64::total_cmp);
+        fixed[a].dedup_by(|x, y| (*x - *y).abs() < eps);
+    }
+
+    let snap = (0.3 * inp.size).min(0.25 * circles.iter().map(|c| c.r).fold(f64::INFINITY, f64::min));
+    for g in &mut groups {
+        let outer = g.circles.first().copied().ok_or("an empty circle group")?;
+        let r0 = outer.r;
+        for a in 0..2 {
+            let c = g.c[a];
+            if !g.patch && fixed[a].iter().any(|v| (v - c).abs() < r0 - eps) {
+                return Err(format!("a face of the body runs through the circle of radius {r0:.4}"));
+            }
+        }
+        let half = match outer.kind {
+            // The square round the whole circle (its corners projected onto it at 45°), or
+            // where a blend it takes in sets a side, at the walls' inner plane.
+            RingKind::Butterfly if g.patch => std::array::from_fn(|a| {
+                let mut h = [r0; 2];
+                // The blends' near edge: the walls' inner plane, whose corner projects onto
+                // the blend's middle.
+                if let Some(b) = g.blends {
+                    if 0.5 * (b[a][0] + b[a][1]) > g.c[a] {
+                        h[1] = b[a][0] - g.c[a];
+                    } else {
+                        h[0] = g.c[a] - b[a][1];
+                    }
+                }
+                h
+            }),
+            RingKind::Butterfly => [[r0 / 2f64.sqrt(); 2]; 2],
+            RingKind::OGrid => o_grid_frame(g, &fixed, eps)?,
+        };
+        for a in 0..2 {
+            let c = g.c[a];
+            for s in 0..2 {
+                let h = half[a][s];
+                if outer.kind == RingKind::Butterfly && !g.patch && fixed[a].iter().any(|v| (v - c).abs() < h - eps) {
+                    return Err(format!("a face of the body runs through the square inside the circle of radius {r0:.4}"));
+                }
+                g.frame[a][s] = if s == 0 { c - h } else { c + h };
+            }
+        }
+    }
+    // Frames that overlap along an axis share their planes there (a plane may not cut another
+    // frame); two frames that overlap along both are one cell, which the layout does not take.
+    for _ in 0..=groups.len() * groups.len() {
+        let mut changed = false;
+        for a in 0..2 {
+            for i in 0..groups.len() {
+                for j in 0..groups.len() {
+                    if i == j {
+                        continue;
+                    }
+                    let (fi, fj) = (groups[i].frame[a], groups[j].frame[a]);
+                    let overlap = fi[0] < fj[1] - eps && fj[0] < fi[1] - eps;
+                    let same = (fi[0] - fj[0]).abs() < eps && (fi[1] - fj[1]).abs() < eps;
+                    if overlap && !same {
+                        let u = [fi[0].min(fj[0]), fi[1].max(fj[1])];
+                        groups[i].frame[a] = u;
+                        groups[j].frame[a] = u;
+                        changed = true;
+                    }
+                }
+            }
+        }
+        if !changed {
+            break;
+        }
+    }
+    for (i, g) in groups.iter().enumerate() {
+        for h in groups.iter().skip(i + 1) {
+            if (0..2).all(|a| g.frame[a][0] < h.frame[a][1] - eps && h.frame[a][0] < g.frame[a][1] - eps) {
+                return Err(format!(
+                    "the circles at ({:.4}, {:.4}) and ({:.4}, {:.4}) are too close for a frame each",
+                    g.c[0], g.c[1], h.c[0], h.c[1]
+                ));
+            }
+        }
+    }
+    // The planes: the fixed ones and the frames, a frame within `snap` of another plane moved
+    // onto it (a fixed plane wins).
+    let mut planes: [Vec<f64>; 3] = fixed.clone();
+    for a in 0..2 {
+        for g in &mut groups {
+            for s in 0..2 {
+                let v = g.frame[a][s];
+                let near = fixed[a].iter().copied().filter(|p| (p - v).abs() < snap).min_by(|p, q| (p - v).abs().total_cmp(&(q - v).abs()));
+                let v = match near {
+                    Some(p) => p,
+                    None => planes[a].iter().copied().find(|p| (p - v).abs() < snap).unwrap_or(v),
+                };
+                g.frame[a][s] = v;
+                planes[a].push(v);
+            }
+        }
+        planes[a].sort_by(f64::total_cmp);
+        planes[a].dedup_by(|x, y| (*x - *y).abs() < eps);
+    }
+    for g in &groups {
+        for a in 0..2 {
+            // A patch's frame may stop short of its circle where the walls join (the ring's
+            // faces there are projected out onto it), but holds the circles inside.
+            let r0 = g.circles.first().map_or(0.0, |c| c.r);
+            let hold = if g.patch { 1.2 * g.circles.get(1).map_or(0.0, |c| c.r) } else { 0.7 * r0 };
+            if !(g.frame[a][0] < g.c[a] - hold && g.frame[a][1] > g.c[a] + hold) {
+                return Err(format!("the frame round the circle of radius {r0:.4} does not hold it"));
+            }
+            if !g.patch && planes[a].iter().any(|p| *p > g.frame[a][0] + eps && *p < g.frame[a][1] - eps) {
+                return Err(format!("a plane of the body runs through the frame round the circle of radius {r0:.4}"));
+            }
+        }
+    }
+    if planes.iter().any(|p| p.len() < 2) {
+        return Err("the body has no planar sides or circles to lay a grid between".into());
+    }
+    let n = planes.each_ref().map(|p| p.len() - 1);
+    if n.iter().product::<usize>() * (1 + 4 * circles.len()) > MAX_LAYOUT_BLOCKS {
+        return Err(format!("a grid of {n:?} cells is too large for one layout"));
+    }
+
+    // The grid, in the local frame; each block's point that says whether it is material.
+    let mut t = Topology::grid([&planes[0], &planes[1], &planes[2]]).map_err(|e| e.to_string())?;
+    let mid = |p: &[f64], i: usize| 0.5 * (p[i] + p[i + 1]);
+    let mut probe: Vec<V3> = t
+        .blocks
+        .iter()
+        .enumerate()
+        .map(|(b, _)| [mid(&planes[0], b % n[0]), mid(&planes[1], (b / n[0]) % n[1]), mid(&planes[2], b / (n[0] * n[1]))])
+        .collect();
+    let index = |p: &[f64], v: f64| p.iter().position(|x| (x - v).abs() < eps);
+    // The grid cells the rings replace.
+    let mut replaced: Vec<usize> = Vec::new();
+    let mut rings = 0;
+    for g in &groups {
+        let (Some(i0), Some(i1), Some(j0), Some(j1)) =
+            (index(&planes[0], g.frame[0][0]), index(&planes[0], g.frame[0][1]), index(&planes[1], g.frame[1][0]), index(&planes[1], g.frame[1][1]))
+        else {
+            return Err("a frame lost its planes".into());
+        };
+        let r0 = g.circles.first().map_or(0.0, |c| c.r);
+        // The squares inside the frame: one per circle (corners at 45° on it), then the core.
+        // Each: half-sides [-u, +u, -v, +v] and the radius it stands for per side (a patch's
+        // frame stands for its circle, which the frame's corners are projected onto).
+        let mut squares: Vec<([f64; 4], [f64; 4])> = Vec::new();
+        let fr = [g.c[0] - g.frame[0][0], g.frame[0][1] - g.c[0], g.c[1] - g.frame[1][0], g.frame[1][1] - g.c[1]];
+        squares.push((fr, if g.patch { [r0; 4] } else { fr }));
+        for c in &g.circles {
+            let h = c.r / 2f64.sqrt();
+            if squares.last().is_some_and(|(s, _)| s.iter().all(|x| (x - h).abs() < eps)) || (g.patch && c.r == r0) {
+                continue;
+            }
+            squares.push(([h; 4], [c.r; 4]));
+        }
+        rings += g.circles.len();
+        let inner = g.circles.last().map_or(0.0, |c| c.r);
+        squares.push(([inner / (2.0 * 2f64.sqrt()); 4], [0.0; 4]));
+        if squares.windows(2).any(|w| (0..4).any(|i| !(w[1].0[i] < w[0].0[i] - eps))) {
+            return Err(format!("the frame round the circle of radius {r0:.4} is too tight for its ring"));
+        }
+        // The frame's subdivision by the grid's planes, as fractions along each side: every
+        // square inside is divided alike, so the ring's blocks meet node to node.
+        let frac = |a: usize, lo: usize, hi: usize| -> Vec<f64> {
+            let (p0, p1) = (planes[a][lo], planes[a][hi]);
+            planes[a][lo..=hi].iter().map(|p| (p - p0) / (p1 - p0)).collect()
+        };
+        let (fu, fv) = (frac(0, i0, i1), frac(1, j0, j1));
+        // Point (u, v) (fractions along the axes) of square `k`.
+        let at = |k: usize, u: f64, v: f64| -> [f64; 2] {
+            let h = squares.get(k).map_or([0.0; 4], |s| s.0);
+            [g.c[0] - h[0] + u * (h[0] + h[1]), g.c[1] - h[2] + v * (h[2] + h[3])]
+        };
+        // The frame's boundary, counter-clockwise, as (u, v) fractions with the side each
+        // segment that starts there lies on (0: -u, 1: +u, 2: -v, 3: +v).
+        let mut around: Vec<([f64; 2], usize)> = Vec::new();
+        around.extend(fu[..fu.len() - 1].iter().map(|&u| ([u, 0.0], 2)));
+        around.extend(fv[..fv.len() - 1].iter().map(|&v| ([1.0, v], 1)));
+        around.extend(fu[1..].iter().rev().map(|&u| ([u, 1.0], 3)));
+        around.extend(fv[1..].iter().rev().map(|&v| ([0.0, v], 0)));
+        for w in 0..n[2] {
+            let (z0, z1) = (planes[2][w], planes[2][w + 1]);
+            let zmid = 0.5 * (z0 + z1);
+            for i in i0..i1 {
+                for j in j0..j1 {
+                    replaced.push((w * n[1] + j) * n[0] + i);
+                }
+            }
+            let add = |q: [[f64; 2]; 4], pr: V3, t: &mut Topology, probe: &mut Vec<V3>| {
+                let base = t.vertices.len() as u32;
+                for z in [z0, z1] {
+                    for p in q {
+                        t.vertices.push([p[0], p[1], z]);
+                    }
+                }
+                let mut b = [base, base + 1, base + 2, base + 3, base + 4, base + 5, base + 6, base + 7];
+                let pos = b.map(|v| t.vertices.get(v as usize).copied().unwrap_or_default());
+                if corner_det(&pos) < 0.0 {
+                    b = [b[0], b[3], b[2], b[1], b[4], b[7], b[6], b[5]];
+                }
+                t.blocks.push(b);
+                probe.push(pr);
+            };
+            for (k, pair) in squares.windows(2).enumerate() {
+                let (outer_rho, inner_rho) = (pair[0].1, pair[1].1);
+                for (s, &(p, side)) in around.iter().enumerate() {
+                    let Some(&(q, _)) = around.get((s + 1) % around.len()) else { continue };
+                    let quad = [at(k, p[0], p[1]), at(k, q[0], q[1]), at(k + 1, q[0], q[1]), at(k + 1, p[0], p[1])];
+                    // The probe: between the two radii the squares stand for, toward the
+                    // segment's middle.
+                    let m = [0.5 * (quad[0][0] + quad[1][0]) - g.c[0], 0.5 * (quad[0][1] + quad[1][1]) - g.c[1]];
+                    let len = m[0].hypot(m[1]).max(eps);
+                    let rho = 0.5 * (outer_rho[side] + inner_rho[side]);
+                    add(quad, [g.c[0] + m[0] / len * rho, g.c[1] + m[1] / len * rho, zmid], &mut t, &mut probe);
+                }
+            }
+            // The core, divided as the frame.
+            let last = squares.len() - 1;
+            for u in fu.windows(2) {
+                for v in fv.windows(2) {
+                    let quad = [at(last, u[0], v[0]), at(last, u[1], v[0]), at(last, u[1], v[1]), at(last, u[0], v[1])];
+                    let cx = 0.25 * quad.iter().map(|p| p[0]).sum::<f64>();
+                    let cy = 0.25 * quad.iter().map(|p| p[1]).sum::<f64>();
+                    add(quad, [cx, cy, zmid], &mut t, &mut probe);
+                }
+            }
+        }
+    }
+    if probe.len() != t.blocks.len() {
+        return Err("the layout lost track of its blocks".into());
+    }
+    replaced.sort_unstable();
+    replaced.dedup();
+    t.remove(&replaced).map_err(|e| e.to_string())?;
+    let mut k = 0;
+    probe.retain(|_| {
+        k += 1;
+        replaced.binary_search(&(k - 1)).is_err()
+    });
+    t.merge(eps);
+
+    // The blend layer: a block on every boundary face of the grid on a side with a layer.
+    let mut uses: std::collections::BTreeMap<[u32; 4], usize> = std::collections::BTreeMap::new();
+    for block in &t.blocks {
+        for f in hex_faces(block) {
+            let mut key = f;
+            key.sort_unstable();
+            *uses.entry(key).or_insert(0) += 1;
+        }
+    }
+    let mut moved: std::collections::BTreeMap<u32, u32> = std::collections::BTreeMap::new();
+    let original = t.blocks.len();
+    for b in 0..original {
+        let Some(block) = t.blocks.get(b).copied() else { continue };
+        for f in hex_faces(&block) {
+            let mut key = f;
+            key.sort_unstable();
+            if uses.get(&key) != Some(&1) {
+                continue;
+            }
+            let pts = f.map(|v| t.vertices.get(v as usize).copied().unwrap_or_default());
+            let side = (0..3).flat_map(|a| [(a, 0), (a, 1)]).find(|&(a, s)| {
+                let plane = if s == 0 { ilo[a] } else { ihi[a] };
+                ring[a][s] > 0.0 && pts.iter().all(|p| (p[a] - plane).abs() < eps)
+            });
+            let Some((a, s)) = side else { continue };
+            let mut outer = [0u32; 4];
+            for (o, &v) in outer.iter_mut().zip(&f) {
+                *o = match moved.get(&v) {
+                    Some(&w) => w,
+                    None => {
+                        let p = t.vertices.get(v as usize).copied().unwrap_or_default();
+                        let mut q = p;
+                        for aa in 0..3 {
+                            if ring[aa][0] > 0.0 && (p[aa] - ilo[aa]).abs() < eps {
+                                q[aa] -= ring[aa][0];
+                            }
+                            if ring[aa][1] > 0.0 && (p[aa] - ihi[aa]).abs() < eps {
+                                q[aa] += ring[aa][1];
+                            }
+                        }
+                        let w = t.vertices.len() as u32;
+                        t.vertices.push(q);
+                        moved.insert(v, w);
+                        w
+                    }
+                };
+            }
+            let mut nb = [f[0], f[1], f[2], f[3], outer[0], outer[1], outer[2], outer[3]];
+            let at = |v: u32| t.vertices.get(v as usize).copied().unwrap_or_default();
+            if corner_det(&nb.map(at)) < 0.0 {
+                nb = [f[0], f[3], f[2], f[1], outer[0], outer[3], outer[2], outer[1]];
+            }
+            let centre = pts.iter().fold([0.0; 3], |acc, p| [acc[0] + p[0] / 4.0, acc[1] + p[1] / 4.0, acc[2] + p[2] / 4.0]);
+            let mut pr = centre;
+            pr[a] += if s == 0 { -0.5 * ring[a][s] } else { 0.5 * ring[a][s] };
+            t.blocks.push(nb);
+            probe.push(pr);
+        }
+    }
+    if t.blocks.len() > MAX_LAYOUT_BLOCKS {
+        return Err(format!("{} blocks: too many for one layout", t.blocks.len()));
+    }
+
+    // Carve: blocks whose probe lies outside the body.
+    let gone: Vec<usize> = probe.iter().enumerate().filter(|(_, p)| winding(inp.mesh, world(**p)) < 0.5).map(|(b, _)| b).collect();
+    if gone.len() == t.blocks.len() {
+        return Err("every block of the layout lies outside the body".into());
+    }
+    if !gone.is_empty() {
+        t.remove(&gone).map_err(|e| e.to_string())?;
+    }
+    for v in &mut t.vertices {
+        *v = world(*v);
+    }
+    t.check().map_err(|e| format!("the layout's blocks do not fit: {e}"))?;
+    let layers = (0..3)
+        .flat_map(|a| [(a, 0), (a, 1)])
+        .filter(|&(a, s)| ring[a][s] > 0.0)
+        .map(|(a, s)| (SIDE_NAMES[perm[a]][s].to_string(), ring[a][s], what[a][s]))
+        .collect();
+    let frames = groups
+        .iter()
+        .map(|g| {
+            let half = (0..2).flat_map(|a| [g.c[a] - g.frame[a][0], g.frame[a][1] - g.c[a]]).fold(f64::INFINITY, f64::min);
+            (world([g.c[0], g.c[1], 0.0]), half)
+        })
+        .collect();
+    Ok(Layout { topology: t, rings, layers, planes: planes.each_ref().map(Vec::len), frames, pillow: None })
+}
+
+/// The ring that takes in the blend with points `pts` (local frame): a blend round a corner of
+/// the outline, touching the body's side along both in-plane axes, that lies inside the frame of
+/// an O-grid ring reaching from the hole to those sides, the hole centred in it. Returns the
+/// group and the frame's half-side per axis (the hole's distance to the side). A frame wider
+/// than 6 radii (or narrower than 1.2) does not take a blend in: the hole is not the corner's.
+fn corner_ring(groups: &[Group], pts: &[V3], lo: V3, hi: V3, eps: f64) -> Option<(usize, [f64; 2])> {
+    let (mut bl, mut bh) = ([f64::INFINITY; 2], [f64::NEG_INFINITY; 2]);
+    for p in pts {
+        for a in 0..2 {
+            bl[a] = bl[a].min(p[a]);
+            bh[a] = bh[a].max(p[a]);
+        }
+    }
+    let tol = 1e3 * eps;
+    groups.iter().enumerate().find_map(|(i, g)| {
+        let outer = g.circles.first()?;
+        if outer.kind != RingKind::OGrid {
+            return None;
+        }
+        let mut half = [0.0; 2];
+        for a in 0..2 {
+            let h = if (bl[a] - lo[a]).abs() < tol {
+                g.c[a] - lo[a]
+            } else if (bh[a] - hi[a]).abs() < tol {
+                hi[a] - g.c[a]
+            } else {
+                return None;
+            };
+            if !(1.2 * outer.r..=6.0 * outer.r).contains(&h) || bl[a] < g.c[a] - h - tol || bh[a] > g.c[a] + h + tol {
+                return None;
+            }
+            half[a] = h;
+        }
+        Some((i, half))
+    })
+}
+
+/// The patch ring that takes in the concave blend with points `pts` (local frame): a blend
+/// inside the square round a boss's whole circle and not inside the circle (the inner fillet
+/// where the walls meet the boss, the boss touching it at most). Returns the group and, per
+/// axis, the blend's extent.
+fn patch_blend(groups: &[Group], pts: &[V3]) -> Option<(usize, [[f64; 2]; 2])> {
+    let (mut bl, mut bh) = ([f64::INFINITY; 2], [f64::NEG_INFINITY; 2]);
+    for p in pts {
+        for a in 0..2 {
+            bl[a] = bl[a].min(p[a]);
+            bh[a] = bh[a].max(p[a]);
+        }
+    }
+    groups.iter().enumerate().find_map(|(i, g)| {
+        let r0 = g.circles.first()?.r;
+        let tol = 1e-3 * r0;
+        if !g.patch || pts.iter().any(|p| (p[0] - g.c[0]).hypot(p[1] - g.c[1]) < 0.9 * r0) {
+            return None;
+        }
+        if (0..2).any(|a| bl[a] < g.c[a] - r0 - tol || bh[a] > g.c[a] + r0 + tol) {
+            return None;
+        }
+        Some((i, [[bl[0], bh[0]], [bl[1], bh[1]]]))
+    })
+}
+
+/// The half-sides of an O-grid ring's frame, per local axis and side: the hole centred in it.
+/// A side of the body within 3 radii (or a corner blend the ring takes in) is the frame on that
+/// side, and the frame's other side is as far from the centre unless the body's side is nearer
+/// there too; an axis with no side near takes the half-side of the other axis's (a square
+/// frame) when that is 1.5 to 3 radii, else 2 radii.
+fn o_grid_frame(g: &Group, fixed: &[Vec<f64>; 3], eps: f64) -> Result<[[f64; 2]; 2], String> {
+    let r0 = g.circles.first().map_or(0.0, |c| c.r);
+    let mut half: [Option<[f64; 2]>; 2] = [None; 2];
+    for a in 0..2 {
+        let c = g.c[a];
+        let mut dist = [0.0; 2];
+        for (s, d) in dist.iter_mut().enumerate() {
+            *d = fixed[a].iter().map(|v| if s == 0 { c - v } else { v - c }).filter(|x| *x > 0.0).fold(f64::INFINITY, f64::min);
+            if !d.is_finite() {
+                return Err(format!("the hole of radius {r0:.4} has no side of the body round it"));
+            }
+            if *d < 1.05 * r0 {
+                return Err(format!("the hole of radius {r0:.4} is {d:.4} mm from a face: too close for a ring"));
+            }
+        }
+        let near = dist[0].min(dist[1]);
+        half[a] = match g.forced[a] {
+            Some(h) => Some([h; 2]),
+            // The side itself frames the ring when a strip narrower than the radius would be
+            // left between them; the other side keeps the frame centred unless it is near too.
+            None if near <= 3.0 * r0 + eps => Some(dist.map(|d| if d <= 3.0 * r0 + eps { d } else { near })),
+            None => None,
+        };
+    }
+    let square = |b: usize| half[b].map(|h| h[0].min(h[1])).filter(|h| (1.5 * r0 - eps..=3.0 * r0 + eps).contains(h)).unwrap_or(2.0 * r0);
+    Ok([half[0].unwrap_or([square(1); 2]), half[1].unwrap_or([square(0); 2])])
+}
+
+/// The six faces of a hex8 block, as corner cycles.
+fn hex_faces(b: &[u32; 8]) -> [[u32; 4]; 6] {
+    [
+        [b[0], b[1], b[2], b[3]],
+        [b[4], b[5], b[6], b[7]],
+        [b[0], b[1], b[5], b[4]],
+        [b[1], b[2], b[6], b[5]],
+        [b[2], b[3], b[7], b[6]],
+        [b[3], b[0], b[4], b[7]],
+    ]
+}
+
+/// The Jacobian determinant at corner 1 of a hex8 block (positive: right-handed).
+pub(super) fn corner_det(c: &[V3; 8]) -> f64 {
+    dot(sub(c[1], c[0]), cross(sub(c[3], c[0]), sub(c[4], c[0])))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn winding_of_a_cube_is_one_inside_and_zero_outside() {
+        let shape = fieldcraft_geometry::block([0.0; 3], [2.0, 2.0, 2.0]).unwrap();
+        let mesh = shape.tessellate(0.01).unwrap();
+        assert!((winding(&mesh, [1.0, 1.0, 1.0]) - 1.0).abs() < 1e-6);
+        assert!(winding(&mesh, [3.0, 1.0, 1.0]).abs() < 1e-6);
+    }
+}
@@ -0,0 +1,249 @@
+//! Decomposition proposals (#439): for a body with features the plan cannot map, the partition
+//! cuts that box those features into a cell of their own, so the rest of the body is cells the
+//! sweep meshes and only the boxed cell is left to tetrahedra (joined to the hex cells by
+//! pyramids, `mesh.cells`).
+//!
+//! The region is the bounding box of the unmapped features' faces (those not already prismatic
+//! along the sweep), in the frame of the sweep direction and two directions square to it. Each
+//! side of the box becomes a cut one element size outside it, where that plane lies inside the
+//! body, clear of its planar faces and of its curved faces (a cut through a curved face does not
+//! close in the partitions' tessellation); a side with no such plane is left open and the tet
+//! cell reaches the body's boundary there. Decomposing a part into sweepable volumes and a
+//! remainder for a free mesher is the practice of T. D. Blacker, *The Cooper Tool*, Proc. 5th
+//! International Meshing Roundtable, 1996 (docs/meshing/literature.md, B11). The proposal is a
+//! reply, not a change: the agent applies the cuts (`commands`) and meshes the cells.
+
+use fieldcraft_geometry::{Design, FaceSurface};
+use fieldcraft_model::MeshPlan;
+use serde_json::{Value, json};
+
+use super::{AXES, Clearance, V3, cross, dot, faces_prismatic, parallel, plan_shape, unit};
+use crate::Result;
+
+/// The decomposition proposal for `plan`, or `None` when every feature is mapped (or the plan
+/// has no sweep direction to make cells along).
+pub(super) fn proposal(design: &Design, plan: &MeshPlan) -> Result<Option<Value>> {
+    let Some(d) = plan.direction else { return Ok(None) };
+    if plan.unmapped.is_empty() {
+        return Ok(None);
+    }
+    let Some(shape) = plan_shape(design, &plan.body) else { return Ok(None) };
+    let source = design.source_of(&plan.body).unwrap_or(&plan.body);
+    let features: Vec<_> = design.features(Some(source))?.into_iter().next().map(|b| b.features).unwrap_or_default();
+    let surfaces = shape.face_surfaces()?;
+    // The unmapped features whose faces the sweep cannot mesh.
+    let lumps: Vec<_> = features
+        .iter()
+        .filter(|f| plan.unmapped.iter().any(|u| u.id == f.id))
+        .filter(|f| !f.faces.is_empty() && !faces_prismatic(shape, &surfaces, &f.faces, d))
+        .collect();
+    if lumps.is_empty() {
+        return Ok(None);
+    }
+    let faces: Vec<u32> = lumps.iter().flat_map(|f| &f.faces).filter_map(|n| shape.face_index(n)).collect();
+    let m = shape.measure()?;
+    let diagonal = (0..3).map(|k| (m.bbox_max[k] - m.bbox_min[k]).powi(2)).sum::<f64>().sqrt();
+    let mesh = shape.tessellate(plan.tolerance.unwrap_or(1e-3 * diagonal))?;
+    // The frame: the sweep direction and two directions square to it (axes when it is one).
+    let side = AXES.iter().copied().filter(|a| !parallel(*a, d)).min_by(|a, b| dot(*a, d).abs().total_cmp(&dot(*b, d).abs())).unwrap_or(AXES[0]);
+    let e1 = unit(cross(d, side)).unwrap_or(side);
+    let e2 = unit(cross(d, e1)).unwrap_or(side);
+    let frame = [d, e1, e2].map(|a| AXES.iter().copied().find(|x| parallel(*x, a)).unwrap_or(a));
+    let mut lo = [f64::INFINITY; 3];
+    let mut hi = [f64::NEG_INFINITY; 3];
+    let mut curved: Vec<Vec<V3>> = vec![Vec::new(); surfaces.len()];
+    for (t, &f) in mesh.triangles.iter().zip(&mesh.tri_face) {
+        let pts: Vec<V3> = t.iter().filter_map(|&i| mesh.positions.get(i as usize).copied()).collect();
+        if faces.contains(&f) {
+            for p in &pts {
+                for (k, a) in frame.iter().enumerate() {
+                    lo[k] = lo[k].min(dot(*p, *a));
+                    hi[k] = hi[k].max(dot(*p, *a));
+                }
+            }
+        }
+        if !matches!(surfaces.get(f as usize), Some(Some(FaceSurface::Plane { .. })))
+            && let Some(c) = curved.get_mut(f as usize)
+        {
+            c.extend(pts);
+        }
+    }
+    if lo.iter().chain(&hi).any(|v| !v.is_finite()) {
+        return Ok(None);
+    }
+    curved.retain(|p| !p.is_empty());
+    let planes = surfaces
+        .iter()
+        .zip(shape.faces())
+        .filter_map(|(s, f)| match s {
+            Some(FaceSurface::Plane { normal, point }) => Some((*normal, dot(*normal, *point), f.name.as_str())),
+            _ => None,
+        })
+        .collect();
+    let corners = (0..8)
+        .map(|i| {
+            [
+                if i & 1 == 0 { m.bbox_min[0] } else { m.bbox_max[0] },
+                if i & 2 == 0 { m.bbox_min[1] } else { m.bbox_max[1] },
+                if i & 4 == 0 { m.bbox_min[2] } else { m.bbox_max[2] },
+            ]
+        })
+        .collect();
+    let body = Clearance { corners, planes, curved, gap: 0.5 * plan.size };
+    let names: Vec<&str> = lumps.iter().map(|f| f.name.as_str()).collect();
+    let mut cuts = Vec::new();
+    let mut open = Vec::new();
+    let mut region = [[0.0; 3]; 2];
+    for (k, n) in frame.iter().enumerate() {
+        let (blo, bhi) = body.extent(*n);
+        region[0][k] = blo;
+        region[1][k] = bhi;
+        for (end, t) in [(0, lo[k] - plan.size), (1, hi[k] + plan.size)] {
+            let which = if end == 0 { "below" } else { "above" };
+            let why = if !body.inside(*n, t) {
+                Some("the body ends there".to_string())
+            } else if let Some((_, face)) = body.faces_near(*n, t).next() {
+                Some(format!("it would lie on face `{face}`"))
+            } else if body.crosses_curved(*n, t) {
+                Some("it would cross a curved face".into())
+            } else {
+                None
+            };
+            match why {
+                Some(why) => open.push(json!({"normal": n, "side": which, "reason": why})),
+                None => {
+                    region[end][k] = t;
+                    let point = n.map(|c| c * t);
+                    cuts.push(json!({"point": point, "normal": n, "reason": format!("boxes {} ({which} along {n:?})", names.join(", "))}));
+                }
+            }
+        }
+    }
+    // The commands that make the cuts and mesh the cells (the boxed cell falls back to tet).
+    let mut commands = Vec::new();
+    for (i, c) in cuts.iter().enumerate() {
+        let name = format!("{}-split{}", plan.body, i + 1);
+        commands.push(json!({"command": "geometry.datum", "params": {"name": name, "by": {"type": "point_normal", "point": c["point"], "normal": c["normal"]}}}));
+        commands.push(json!({"command": "geometry.partition", "params": {"name": name, "datum": name}}));
+    }
+    commands.push(json!({"command": "mesh.cells", "params": {"default": "auto", "size": plan.size, "transition": "pyramid"}}));
+    let box_volume: f64 = (0..3).map(|k| region[1][k] - region[0][k]).product();
+    let share = if m.volume.abs() > 0.0 { (box_volume / m.volume.abs()).min(1.0) } else { 1.0 };
+    Ok(Some(json!({
+        "features": names,
+        "cuts": cuts,
+        "open_sides": open,
+        "tet_region": {"frame": frame, "min": region[0], "max": region[1]},
+        "tet_share_at_most": share,
+        "commands": commands,
+        "note": "cut the body by these planes; the cell inside `tet_region` is meshed with tet, every other cell is a box or a slice of the sweep's cross-section the hex meshers take, and mesh.cells joins the tet cell to them through pyramids",
+    })))
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::BTreeSet;
+
+    use serde_json::{Value, json};
+
+    use crate::Session;
+
+    /// A 80 × 40 × 12 plate with a ball (radius 8) joined on its top: the sweep takes the plate,
+    /// not the dome.
+    fn plate_with_dome() -> (crate::tests::TempDir, Session) {
+        let commands = json!({"commands": [
+            {"command": "solid.box", "params": {"length": 80, "width": 40, "height": 12, "body_name": "Plate"}},
+            {"command": "solid.sphere", "params": {"center": [60, 20, 12], "radius": 8, "body_name": "Ball", "operation": "new"}},
+            {"command": "solid.combine", "params": {"target": "Plate", "tools": ["Ball"], "operation": "join"}},
+        ]});
+        let bytes = fieldcraft_geometry::script_design(&commands.to_string()).unwrap();
+        let (dir, path) = crate::tests::design_file(&bytes);
+        let mut s = Session::default();
+        s.execute("geometry.open", &json!({"path": path})).unwrap();
+        (dir, s)
+    }
+
+    /// Fix the end x = 0, pull the end x = 80 with `force` (N), solve, and return the mean
+    /// displacement of the loaded end along `k`.
+    fn pull(s: &mut Session, force: [f64; 3], k: usize) -> f64 {
+        let m = &s.model;
+        let at = |x: f64| -> Vec<u32> { m.nodes().iter().filter(|(_, n)| (n.xyz[0] - x).abs() < 1e-6).map(|(l, _)| *l).collect() };
+        let (root, tip) = (at(0.0), at(80.0));
+        // The loaded end's element faces, so the force is shared by consistent weights.
+        let end: Vec<Value> = m
+            .elements()
+            .iter()
+            .flat_map(|(&e, el)| (1..=el.kind.faces().len() as u8).map(move |f| (e, f)))
+            .filter(|&(e, f)| {
+                m.face_nodes(fieldcraft_model::ElementFace { element: e, face: f })
+                    .is_some_and(|ns| ns.iter().all(|n| (m.node(*n).unwrap().xyz[0] - 80.0).abs() < 1e-6))
+            })
+            .map(|(e, f)| json!({"element": e, "face": f}))
+            .collect();
+        let script = json!([
+            {"command": "model.set.create", "params": {"name": "all", "elements": m.elements().keys().collect::<Vec<_>>()}},
+            {"command": "model.set.create", "params": {"name": "root", "nodes": root}},
+            {"command": "model.set.create", "params": {"name": "tip", "faces": end}},
+            {"command": "model.material.create", "params": {"name": "Steel", "elastic": {"type": "isotropic", "young": 210000, "poisson": 0.3}}},
+            {"command": "model.section.create", "params": {"name": "S", "set": "all", "material": "Steel", "kind": {"type": "solid"}}},
+            {"command": "model.boundary_condition.create", "params": {"name": "Clamp", "type": "fixed", "target": {"set": "root"}}},
+            {"command": "model.load.create", "params": {"name": "Pull", "type": "force", "target": {"set": "tip"}, "vector": force}},
+            {"command": "model.step.create", "params": {"name": "Load", "procedure": {"type": "static"}, "boundary_conditions": ["Clamp"], "loads": ["Pull"]}},
+        ]);
+        s.run_script(&script).unwrap();
+        s.execute("solve.static", &json!({})).unwrap();
+        let probe = s.execute("solve.probe", &json!({"step": "Load", "nodes": tip})).unwrap();
+        let w: Vec<f64> = probe["nodes"].as_array().unwrap().iter().map(|n| n["displacement"][k].as_f64().unwrap()).collect();
+        w.iter().sum::<f64>() / w.len() as f64
+    }
+
+    /// #439's acceptance: the plan proposes cuts that box the dome; with them the plate is hex
+    /// cells and the dome's cell tet, joined by pyramids into one valid, conforming mesh whose
+    /// static answer matches the all-tet mesh's within 2 %.
+    #[test]
+    fn a_dome_on_a_plate_is_boxed_into_a_tet_cell_and_the_rest_is_hex() {
+        let (_dir, mut s) = plate_with_dome();
+        let plan = s.execute("mesh.plan", &json!({"body": "Plate", "size": 4})).unwrap();
+        let d = &plan["decomposition"];
+        assert!(d["features"].as_array().is_some_and(|f| !f.is_empty()), "{plan}");
+        let cuts = d["cuts"].as_array().unwrap();
+        assert!(cuts.len() >= 4, "{d}");
+        let commands: Vec<Value> = d["commands"].as_array().unwrap().clone();
+        let (cut_commands, mesh) = commands.split_at(commands.len() - 1);
+        s.run_script(&json!(cut_commands)).unwrap();
+        // The cell inside the region is tet; the others take the default (auto: hex).
+        let (lo, hi) = (&d["tet_region"]["min"], &d["tet_region"]["max"]);
+        let bodies = s.execute("geometry.bodies", &json!({})).unwrap();
+        // The region is given along its frame's axes (here coordinate axes).
+        let axis = |k: usize| (0..3).find(|&i| d["tet_region"]["frame"][k][i].as_f64().unwrap().abs() > 0.5).unwrap();
+        let inside = |b: &Value| {
+            (0..3).all(|k| {
+                let i = axis(k);
+                b["bbox"][0][i].as_f64().unwrap() >= lo[k].as_f64().unwrap() - 1e-6
+                    && b["bbox"][1][i].as_f64().unwrap() <= hi[k].as_f64().unwrap() + 1e-6
+            })
+        };
+        let tet: Vec<String> = bodies.as_array().unwrap().iter().filter(|b| inside(b)).map(|b| b["name"].as_str().unwrap().to_string()).collect();
+        assert_eq!(tet.len(), 1, "{bodies}");
+        let mut params = mesh[0]["params"].clone();
+        params["methods"] = json!({tet[0].clone(): "tet"});
+        let r = s.execute("mesh.cells", &params).unwrap();
+        let kinds: BTreeSet<&str> = s.model.elements().values().map(|e| e.kind.name()).collect();
+        assert_eq!(kinds.into_iter().collect::<Vec<_>>(), ["hex8", "pyramid5", "tet4"], "{r}");
+        assert!(r["interfaces"].as_array().unwrap().iter().all(|i| i["joined"] != "tied"), "{r}");
+        let dup = s.execute("mesh.check.duplicates", &json!({})).unwrap();
+        assert_eq!(dup["counts"], json!({"coincident": 0, "cracks": 0, "duplicate_elements": 0, "free_edges": 0}), "{dup}");
+        let q = s.execute("mesh.quality", &json!({})).unwrap();
+        assert_eq!(q["invalid"]["count"], 0, "{q}");
+        // Tension along the plate, which the dome stiffens locally. (In bending, linear hexahedra
+        // and linear tetrahedra lock differently at three elements through the thickness, so
+        // the two meshes would differ by their discretisation, not by the transition.)
+        let hex = s.model.elements().values().filter(|e| e.kind.name() == "hex8").count();
+        let mixed = pull(&mut s, [8000.0, 0.0, 0.0], 0);
+        let (_dir2, mut t) = plate_with_dome();
+        t.execute("mesh.tet.generate", &json!({"body": "Plate", "size": 4})).unwrap();
+        let all_tet = pull(&mut t, [8000.0, 0.0, 0.0], 0);
+        eprintln!("mixed {mixed:.6e} ({hex} hex of {} elements), all tet {all_tet:.6e}", s.model.elements().len());
+        assert!(((mixed - all_tet) / all_tet).abs() < 0.02, "{mixed} vs {all_tet}");
+    }
+}
				`@@ -0,0 +1 @@`
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				`@@ -0,0 +1 @@`
				`{"shapes": [{"d": "M3 8 L12 4 L21 8 L12 12 Z", "fill": "soft", "stroke": "line"}, {"d": "M3 8 L3 16 L12 20 L12 12 M12 20 L21 16 L21 8", "stroke": "line"}, {"d": "M14.5 5.1 L17 6.2 L8 10.3 L5.5 9.2 Z", "fill": "warm", "stroke": "warm", "width": 1}, {"d": "M3 8 L12 4 L21 8 L12 12 Z", "stroke": "accent", "width": 1.75}]}`
				`@@ -0,0 +1 @@`
				`{"shapes": [{"d": "M3 6 L10.5 6 L10.5 18 L3 18 Z", "fill": "soft", "stroke": "line"}, {"d": "M13.5 6 L21 6 L21 18 L13.5 18 Z", "fill": "soft", "stroke": "line"}, {"line": [9, 8.5, 15, 8.5], "stroke": "warm", "width": 1.75}, {"line": [9, 12, 15, 12], "stroke": "warm", "width": 1.75}, {"line": [9, 15.5, 15, 15.5], "stroke": "warm", "width": 1.75}]}`
				`@@ -0,0 +1 @@`
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				`@@ -0,0 +1 @@`
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				`@@ -0,0 +1 @@`
				`{"shapes": [{"d": "M6 20 L18 20 L18 11.6 Q12 8.4 6 11.6 Z", "fill": "soft", "stroke": "line"}, {"d": "M6 17.2 L18 17.2 M6 14.4 Q12 12 18 14.4 M10 20 L10 9.9 M14 20 L14 9.9", "stroke": "accent", "width": 1}, {"d": "M3 9.2 Q12 3.4 21 9.2", "stroke": "accent", "width": 2}, {"d": "M12 6 L12 3 M10.5 4.5 L12 3 L13.5 4.5", "stroke": "line"}]}`
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				`@@ -0,0 +1 @@`
				`{"shapes": [{"d": "M12 3 L20 7 L20 16 L12 20 L4 16 L4 7 Z", "fill": "soft", "stroke": "line"}, {"d": "M4 7 L12 11 L20 7 M12 11 L12 20", "stroke": "line"}, {"d": "M4 11.5 L12 15.5 L20 11.5 M8 9 L8 18 M16 9 L16 18", "stroke": "accent", "width": 1}, {"d": "M12 3 L12 5.4 M20 7 L15.2 7 M12 11 L12 8.6 M4 7 L8.8 7", "stroke": "accent", "width": 1}, {"d": "M8.8 7 A3.2 1.6 0 1 0 15.2 7 A3.2 1.6 0 1 0 8.8 7 Z", "stroke": "warm", "width": 1.5}]}`
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