chore(task): archive 08-03-extract-building-module

.trellis/tasks/archive/2026-08/08-03-extract-building-module/implement.md

@@ -0,0 +1,47 @@
+# Implementation Plan
+
+## Checklist
+
+1. Capture a parity baseline before product-code edits.
+2. Add `blender/osmassets/building.py` with the current building assembly and
+   detail helper logic.
+3. Import `building.py` in `blender/generate_scene.py`.
+4. Remove inline `_assemble_building()` and `add_building_details()` from
+   `generate_scene.py`.
+5. Replace the building call site with `building.assemble(...)`, passing
+   `args["office_overrides"]` instead of the full `args` dict.
+6. Run Python validation:
+   - `python3 -m py_compile blender/osmassets/building.py`
+   - `python3 -m py_compile blender/generate_scene.py`
+   - `python3 -m unittest blender/tests/test_pure.py`
+7. Capture parity after the refactor.
+8. Compare before/after parity snapshots and inspect any non-ignored diff.
+9. Update `.trellis/spec` and `docs/changelog.md` only for durable status or
+   convention changes discovered during implementation.
+10. Commit, archive the task, and record the journal entry.
+
+## Validation Commands
+
+```bash
+node scripts/parity.js capture building-module-before --stages blender,cesium
+python3 -m py_compile blender/osmassets/building.py
+python3 -m py_compile blender/generate_scene.py
+python3 -m unittest blender/tests/test_pure.py
+node scripts/parity.js capture building-module-after --stages blender,cesium
+node scripts/parity.js compare building-module-before building-module-after
+```
+
+## Risk Points
+
+- Passing `office_overrides` instead of `args` changes the function contract;
+  verify `office_override` custom properties and industrial classification via
+  parity.
+- `Building_<way_id>_Windows` mesh construction depends on `MeshBatch` object
+  naming and `add_wall_panel()` geometry; copy it mechanically.
+- `make_prism()` can return `None` on degenerate input, but the current call
+  site filters `len(ring) >= 3`. Preserve the existing behavior and return
+  tuple shape.
+- Do not reorder building material creation or catalog entries; material order
+  affects GLB material indices.
+- Parity is mandatory because this is a pure refactor of bpy-layer scene
+  generation.