Rename the project to FieldCraft

Crates fieldcraft-*, binaries fieldcraft and fieldcraft-cli, the .fieldcraft file (format tag
fieldcraft/1, manifest fieldcraft.json), FIELDCRAFT_* environment variables, the MCP server
name, egui widget ids (fc_*), the app icon document FieldCraft.icon and its generated family,
docs and licences. No compatibility shim: no files of the earlier name exist.

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

docs/formats/fieldcraft.md

@@ -0,0 +1,94 @@
+# The `.fieldcraft` file (format `fieldcraft/1`)
+
+A `.fieldcraft` file holds one model: its definition, its mesh, the geometry it is built on and
+the commands that built it. It is written and read by `fieldcraft-io` (`write`, `read`; bytes in,
+bytes out, so the browser build uses the same code) and by the commands `file.save`,
+`file.save_as` and `file.open`.
+
+## Package
+
+The file is a ZIP package with exactly four parts, in this order, all stored uncompressed (so any
+unzip tool reads them: `unzip -p bracket.fieldcraft model.json`):
+
+| Part | Content |
+|---|---|
+| `fieldcraft.json` | Manifest: `format` (`"fieldcraft/1"`), `generator` (`"FieldCraft 0.1.0"`), `geometry`, and `parts`: the byte size and SHA-256 of each other part. |
+| `model.json` | The model definition: unit system, sets, materials, sections, reference points, couplings, boundary conditions, loads and steps. Pretty-printed JSON with a fixed key order (maps sorted by name), so a change shows as a line diff. Its form is the model's own JSON form, which commands take as parameters. |
+| `mesh.bin` | Nodes, elements and geometry tags, binary (below). |
+| `journal.json` | The commands that built the model, `[{"command": id, "params": {...}}, ...]`, one per line. It is a script `fieldcraft-cli run` replays. |
+
+The same model gives the same bytes on every platform: entry times are fixed (1980-01-01),
+permissions are fixed, and every map is written in sorted order. To diff two versions with git,
+add `*.fieldcraft diff=fieldcraft` to `.gitattributes` and
+`git config diff.fieldcraft.textconv "unzip -p"`; the definition and the journal show line by
+line, the mesh part as binary.
+
+## Geometry
+
+```json
+"geometry": {
+  "design": {"path": "plate.solidcraft", "sha256": "…"},
+  "meshes": [{"path": "/parts/tet.3mf", "sha256": "…"}]
+}
+```
+
+`design` is the SolidCraft design (`geometry.open`), `meshes` the face-tagged 3MF files
+(`geometry.import.mesh`) in import order. Each records the SHA-256 of the bytes that were opened.
+Paths inside the model file's folder are stored relative to it (with `/`), others absolute.
+Opening the model opens each file again: a missing, unreadable or changed file (its hash differs)
+is reported as a warning and the model still opens; sets bind to geometry names, so a remesh
+brings the mesh in line with a changed design. A geometry file that could not be opened keeps its
+reference, so saving again does not lose it.
+
+## `mesh.bin`
+
+Little-endian:
+
+```
+"MCMESH01"                                    magic (the mesh encoding's version is 01)
+u64 nodes, u64 elements, u64 entities, u64 tagged elements, u64 tagged nodes
+nodes      × { u32 label, f64 x, f64 y, f64 z }             labels strictly ascending
+elements   × { u32 label, u8 kind, u32 node × n(kind) }     labels strictly ascending
+entities   × { u8 kind (0 body, 1 face, 2 edge, 3 vertex),
+               u16 length, body name, [u16 length, entity name] unless a body }   UTF-8
+tagged elements × { u32 element, u32 region (0xFFFFFFFF none),
+                    u8 n, n × { u8 face, u32 tag }, u8 n, n × { u8 edge, u32 tag } }
+tagged nodes × { u32 node, u32 tag }
+```
+
+Element kind codes: 1 rod2, 2 beam2, 3 tri3, 4 tri6, 5 quad4, 6 quad8, 7 tet4, 8 tet10, 9 wedge6,
+10 hex8, 11 hex20. Node order is the model's (Abaqus/VTK). A tag indexes the entity list, which
+lists each geometry entity once. Coordinates keep every bit (signed zero included).
+
+## Reading a file safely
+
+Every file is treated as hostile:
+
+- The file is at most 8 GiB; the manifest, definition and journal parts at most 256 MiB each. No
+  allocation is larger than the input.
+- Only the four parts, each once. The ZIP CRC and the manifest's size and SHA-256 are checked for
+  every part.
+- A `format` other than `fieldcraft/1` is refused: a later `fieldcraft/N` as a version error, any
+  other value as not a FieldCraft file. Unknown fields are errors.
+- `mesh.bin`: counts are capped (50 million nodes and elements, one million entities) and checked
+  against the bytes present before anything is read; labels must ascend; unknown kinds and
+  trailing bytes are refused.
+- The model is rebuilt through the same checked methods commands use: names, references,
+  finite coordinates within ±1e9, element connectivity, tag dimensions. A file cannot hold what
+  commands would refuse.
+
+## Saving
+
+`file.save` writes the bytes to a temporary file beside the target, flushes it, keeps the old
+file as `<file>.bak`, renames the new file over the target and flushes the folder: a crash at any
+moment leaves the old file or the new one. A path that exists and is not a regular file is
+refused.
+
+## Autosave and recovery
+
+The desktop app autosaves every 30 seconds while there are unsaved changes, into the recovery
+folder (`FIELDCRAFT_RECOVERY_DIR`, else `FieldCraft/recovery` in the per-user data folder):
+`<id>.fieldcraft`, `<id>.json` (the model's own path, time, counts) and `<id>.lock`, held while
+the app runs. Saving (or undoing back to the saved state) drops the autosave. After a crash, the
+next launch reports the entries; `file.recovery.list` lists them, `file.recover` opens one as
+unsaved work under its original path, and `file.recovery.discard` deletes them.