Design file format 2 with a migration chain (doc::format: older formats upgraded step by step, newer refused with a message, out-of-range numbers and broken occurrence placements refused); a corpus of designs saved by the M0, components-era, joints-era and current builds that must open and evaluate as saved (two pre-versioning behaviour changes listed with their reasons); damaged and hostile variants of every corpus file never panic

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

apps/solvecraft-cli/tests/corpus/README.md

@@ -0,0 +1,20 @@
+# Design file corpus
+
+Designs saved by older SolveCraft builds. `tests/design_corpus.rs` opens each one with the
+current build and checks that it evaluates as it did when saved (the `.expected.json` next to
+it is `solvecraft-cli eval` of that file by the build that saved it: bodies, volumes, areas,
+world bounding boxes), that it is upgraded to the current file format, and that damaged and
+hostile variants of it never panic.
+
+| File | Saved by | Era |
+|---|---|---|
+| `m0-box-fillet-hole` | 3714342 | M0: sketch, parameters, extrude, fillet, cut |
+| `m0-revolve-primitives` | 3714342 | M0: revolve, primitives, combine, chamfer, timeline edit |
+| `components-arm` | 97d03e3 | components and occurrences: move, copy, Paste New, ground |
+| `joints-hinge` | c2309eb | joints: revolute hinge driven by a parameter |
+| `modern-sheet-metal` | bd98035 | sheet metal contour flange (oracle 72) |
+| `modern-path-pattern` | bd98035 | pattern on path (oracle 53) |
+| `modern-plastic` | bd98035 | shell, lip, boss, rest, snap fit, plastic rule |
+
+The scripts that made them are in `scripts/`. Never regenerate a file with a newer build: the
+point is that it was written by the old one. Add new files for new eras instead.