Housekeeping ahead of the Inc 1-4 coverage work

- inventory.py --methods: report the instance methods the app calls per class,
  plus chained calls that constrain a return type. --check says which classes
  to bind; this says what to bind on them, which is what writing ~38 module
  TUs needs.
- Drop StlAPI from the inventory: StlAPI_Writer has no app call site (the only
  use was a test fixture, now on the app's own STL writer). 138 symbols / 47
  modules.
- adding-symbols.md: scope the executing-constructor ban to the BRepAlgoAPI
  booleans, which are the only classes with a deferred Set*/Build form —
  BRepMesh_IncrementalMesh, GeomAPI_*, BRepCheck_Analyzer and friends compute
  in their constructor by design and bind as stock. Replace the per-increment
  app-test guidance: backend/tests/conftest.py imports n3xd.main, so no app
  test can collect until the last module is bound. Increments gate on
  stock-recorded fixtures here; the app suite is the Inc 4 gate.
- parity_venv.sh: run the ocp suite in the swapped venv (it imports only
  OCP/n3xd_ocp, so it works throughout).
- Fix a stale macro name in occt_handle.h (ocp_new, not OCP_TRANSIENT_NEW) and
  drop the unused ocp_transient_class helper.

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

docs/adding-symbols.md

@@ -6,15 +6,22 @@ Read [design.md](design.md) first if you are touching the machinery instead.
 ## 1. Find what is missing
 
 ```bash
-python tools/inventory.py --emit    # re-scan the app for OCP usage
-python tools/inventory.py --check   # what the installed wheel lacks, by module
+python tools/inventory.py --emit                       # re-scan the app for OCP usage
+python tools/inventory.py --check                      # what the wheel lacks, by module
+python tools/inventory.py --methods --only BRepAdaptor # what to bind on each class
 ```
 
-`--check` groups gaps by module, which is how increments are scoped. Note it
-only sees symbols reached through an import (`TopExp.MapShapes_s`), not methods
-called on instances (`shape.IsSame(...)`) — a green `--check` is necessary, not
-sufficient. Running the app's own tests in the parity venv is what catches the
-rest, loudly, as an `AttributeError`.
+`--check` groups gaps by module, which is how increments are scoped. It only
+sees symbols reached through an import (`TopExp.MapShapes_s`), so it answers
+*which* classes to bind but not *what* to bind on them.
+
+`--methods` answers the second question: it resolves variables assigned
+straight from a constructor and reports the methods called on them, plus
+chained calls as `Klass.Outer() -> Inner` (those constrain `Outer`'s **return**
+type — `adaptor.Cylinder().Radius()` is a requirement on `gp_Cylinder`). It is
+a heuristic — it does not follow arguments, returns or attributes, and a local
+reassigned from something else shows up as noise — so read it as a starting
+surface, not a specification.
 
 ## 2. Write the module
 
@@ -50,8 +57,13 @@ only in that a base class must precede its derived classes.
   `nb::class_` declaration and bind constructors with `ocp_new<T, Args...>()`.
   Never `nb::init<>` — see design.md.
 - **Long kernel call** → `OCP_NOGIL`, but only if it cannot re-enter Python.
-- **Executing constructor** → do not bind it. Bind the default constructor plus
-  the `SetX`/`Build` sequence.
+- **Executing constructor** → banned only where a deferred `SetX`/`Build` API
+  exists and the constructor duplicates `Build()`: the `BRepAlgoAPI_*` booleans
+  and splitter. Bind their default constructor plus the `SetX`/`Build`
+  sequence. Classes that only compute in their constructor and have no deferred
+  form — `BRepMesh_IncrementalMesh`, `BRepCheck_Analyzer`, `GeomAPI_*`,
+  `BRepClass3d_SolidClassifier`, `BRepExtrema_DistShapeShape`, `GCPnts_*`,
+  `BRepBuilderAPI_Transform` — bind exactly as stock does.
 - **Enum** → `nb::is_arithmetic()` and `.export_values()`.
 - **`Message_ProgressRange` parameters** → omit them. The app never passes one
   (no `OCP.Message` import anywhere), and leaving them out keeps signatures
@@ -82,11 +94,18 @@ make publish
 tools/parity_venv.sh && python tools/inventory.py --check
 ```
 
-Then run the slice of the app's suite the increment claims — Inc 1 is gated on
-`backend/tests/test_geom_memo.py`, Inc 2 on the tessellation tests plus
-`pytest -m perf`, Inc 4 on `test_cad_pool.py` and `test_derive.py`, and the
-cutover on the full suite plus `backend/tools/rebuild_sweep.py --diff` over the
-project store.
+**The app's own tests cannot gate an individual increment.** `backend/tests/
+conftest.py` imports `n3xd.main`, which pulls in the whole app and therefore the
+whole OCP surface, so every backend test fails at collection until the last
+module is bound. Increments are gated here instead: `tools/gen_fixtures.py`
+records reference values from the *stock* wheel (counts, `Modified`/`Generated`/
+`IsDeleted` history maps, measured floats) into `tests/data/manifest.json`, and
+`tests/test_inc<N>_*.py` reproduces the same constructions under our wheel.
+Counts and history maps must match exactly; floats compare at rel 1e-9.
+
+The app's full suite is the **Inc 4** gate, run in the parity venv, alongside
+`pytest -m perf` and `backend/tools/rebuild_sweep.py --diff` over the project
+store.
 
 ## Adding to `n3xd_ocp` instead