10C Inc 1: core modeling

Binds the modeling core the app builds every feature out of — 93 of its 138
symbols now resolve, up from 34. New modules: GeomAbs, Geom2d, Geom,
TCollection, TColgp, TColStd, GProp, BRepGProp, Bnd, BRepBndLib, Adaptor3d,
BRepAdaptor, GeomLProp, GeomAPI, BRepBuilderAPI, BOPAlgo, BRepAlgoAPI,
BRepPrimAPI, GC, BRepMesh; gp and BRep_Tool completed.

Three structural decisions:

- BRepBuilderAPI_MakeShape carries Build/Shape/Generated/Modified/IsDeleted for
  every maker in the binding, so the booleans, the primitives and (later) the
  fillet builders all answer the app's duck-typed provenance layer through
  ordinary virtual dispatch. History lists come back copied, so they outlive
  the builder.
- The executing two-argument BRepAlgoAPI constructors stay unbound; operands go
  in through SetArguments/SetTools. Section keeps Init1/Init2, which are plain
  setters. BOPAlgo moved up from Inc 2 — SetGlue needs its enum.
- Adaptor3d is registered although the app never imports it: every method it
  calls on BRepAdaptor_Curve/Surface is a virtual declared there, so binding
  them once on the bases leaves mod_BRepAdaptor.cpp with just constructors.

Gate: tests/test_inc1_modeling.py against reference values gen_fixtures.py now
records from the stock wheel — measurements, per-face area/centroid in map
order, mesh counts, and the boolean history map compared exactly, since that is
the substrate the app's topological naming is built on.

tools/sigdiff.py compares our bound surface against stock's, because a wrong
nb::init<> is silent: MakePrism's five-argument form bound OCCT's semi-infinite
gp_Dir overload (gp_Dir converts from gp_Vec), producing a valid solid of the
wrong shape with the flags shifted along. The fixture digest caught it; sigdiff
finds the class of bug directly, and now reports only one deliberate deviation.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DfriM8XUkn7uYf5Dwe2xo6

docs/adding-symbols.md

@@ -75,9 +75,24 @@ only in that a base class must precede its derived classes.
 When in doubt about a signature, ask the stock wheel rather than guessing:
 
 ```bash
-cd ../app && .venv/bin/python -c "from OCP.BRep import BRep_Tool; print(BRep_Tool.Triangulation_s.__doc__)"
+cd ../app && uv run --project backend python -c \
+  "from OCP.BRep import BRep_Tool; print(BRep_Tool.Triangulation_s.__doc__)"
 ```
 
+And after writing a module, run `make sigdiff`, which asks it about every class
+at once. This is not pedantry about matching upstream — it catches the one
+mistake in this codebase that is both easy to make and silent:
+
+> `nb::init<TopoDS_Shape, gp_Vec, bool, bool, bool>` for `BRepPrimAPI_MakePrism`
+> compiled fine and bound the **wrong constructor**. OCCT's finite-prism
+> overload takes four arguments; the five-argument one takes a `gp_Dir` for a
+> semi-infinite prism, and `gp_Dir` converts implicitly from `gp_Vec`. The
+> result was a valid solid of the wrong shape, with the `Copy` and `Canonize`
+> flags shifted one position along.
+
+Anything `sigdiff` reports is either that bug or a deliberate deviation; if it
+is deliberate, say so in a comment where the class is bound.
+
 ## 4. New toolkits
 
 If the linker cannot find a symbol, the class lives in a toolkit not yet listed