Meshing test corpus built with SolidCraft; assembly placement in open_design (#11)

* geometry: build designs from SolidCraft command scripts (feature scripts)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* geometry: place component bodies through their occurrences when opening a design

An assembly's instances were missing and moved components sat at their own origin.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* Meshing test corpus: 16 SolidCraft recipes, analytic shapes, loader and runner

modelcraft-testkit holds the corpus (tests/corpus/<name>/recipe.json run through SolidCraft's
engine, then opened as a design) and the runner binary behind cargo xtask corpus.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* docs: corpus results, test corpus architecture and the scripts feature; licences

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* corpus: measure each body once, check stage widths, simpler loader and runner

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

---------

Co-authored-by: jyviko <2501648+jyviko@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

docs/architecture.md

@@ -28,6 +28,7 @@ crates in strictly lower layers.
 | L3 | `modelcraft-io` | `.modelcraft` files, result files. | planned |
 | L4 | `modelcraft-engine` | Commands (`CommandSpec`), `Session::execute` with rollback and the panic guard, scripts. | started |
 | L5 | `modelcraft-ui-egui`, `modelcraft-mcp` | Desktop UI, control channel and MCP server. | planned |
+| testkit | `modelcraft-testkit` | Test tooling, a dev-dependency only: the meshing test corpus (`tests/corpus/*/recipe.json`, analytic shapes) and its runner (`cargo xtask corpus`). | started |
 | apps | `modelcraft`, `modelcraft-cli`, `modelcraft-web` | Desktop, command line, browser. | cli started |
 
 Rules beyond the layer order:
@@ -36,6 +37,9 @@ Rules beyond the layer order:
   SolidCraft's `[patch.crates-io]` (its fixed truck crates) does not reach dependents, so the
   workspace repeats it from the same rev; bump both together.
 - Everything below the apps builds for `wasm32-unknown-unknown`.
+- `modelcraft-geometry`'s non-default `scripts` feature builds designs from SolidCraft command
+  scripts (`script_design`, through `solidcraft-engine`) for the test corpus; the library opens
+  designs without it.
 
 ## Meshing pipeline
 
@@ -43,6 +47,8 @@ Rules beyond the layer order:
    so feature edges and face-based loads and BCs survive meshing. Faces of an opened design also
    carry SolidCraft's persistent names (`F2:side:l4`, from the feature and sketch curve that made
    them), so a load on a named face follows it when the design is edited and opened again.
+   Bodies of components are placed in the world through their occurrences (one body per
+   placement), as SolidCraft displays and exports them.
 2. **Surface preparation.** Weld coincident vertices, check the surface is closed, manifold and
    consistently oriented, find feature edges (face boundaries, sharp dihedral angles).
 3. **Tetrahedral meshing.** Bowyer–Watson Delaunay on Shewchuk's adaptive predicates (symbolic
@@ -66,3 +72,16 @@ Every user-visible action is a `CommandSpec` in `crates/engine/src/cmd/<area>.rs
 form. `Session::execute` clones the model, runs the command under `catch_unwind`, and restores
 the model on an error or a panic; commands that changed the model are journalled, so the
 journal replays as a script.
+
+## Test corpus
+
+Meshers are measured on our own parts (`docs/adr/0001-libraries.md`, test geometry). Each part is
+a SolidCraft command script in `tests/corpus/<name>/recipe.json` (the file `solidcraft-cli run`
+takes, plus a `corpus` object with its categories and, when it has one, its closed-form volume)
+with a one-line `README.md`; analytic shapes (sphere, torus, cylinder, thick-walled pipe, plate
+with a hole) are generated in code. `modelcraft-testkit` runs a recipe in SolidCraft's engine,
+saves the design and opens it through `open_design`, the path a person's design takes, so no
+geometry is stored. `cargo xtask corpus` (a release build of the testkit's `corpus` binary)
+builds every part, tessellates it and runs each stage of `modelcraft_testkit::runner`, writing
+docs/meshing/corpus.md. A mesher joins by implementing `runner::Stage` (its columns, and a run
+over the part's tessellated surfaces) and adding itself to `runner::stages()`.