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

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

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+# Implementation Plan
+
+## Checklist
+
+1. Capture a parity baseline before product-code edits.
+2. Add `blender/osmassets/roads.py` with current GeoJSON road layer assembly
+   and OSM fallback logic.
+3. Import `roads.py` in `blender/generate_scene.py`.
+4. Remove inline `add_geojson_layer()` from `generate_scene.py`.
+5. Replace the GeoJSON road layer call site with
+   `roads.assemble_geojson_layer(...)`.
+6. Replace the OSM fallback loop with `roads.assemble_osm_fallback(...)`.
+7. Run Python validation:
+   - `python3 -m py_compile blender/osmassets/roads.py`
+   - `python3 -m py_compile blender/generate_scene.py`
+   - `python3 -m unittest blender/tests/test_pure.py`
+8. Capture parity after the refactor.
+9. Compare before/after parity snapshots and inspect any non-ignored diff.
+10. Update `.trellis/spec` and `docs/changelog.md` only for durable status or
+    convention changes discovered during implementation.
+11. Commit, archive the task, and record the journal entry.
+
+## Validation Commands
+
+```bash
+node scripts/parity.js capture road-module-before --stages blender,cesium
+python3 -m py_compile blender/osmassets/roads.py
+python3 -m py_compile blender/generate_scene.py
+python3 -m unittest blender/tests/test_pure.py
+node scripts/parity.js capture road-module-after --stages blender,cesium
+node scripts/parity.js compare road-module-before road-module-after
+```
+
+## Risk Points
+
+- `ROAD_LAYERS` order is load-bearing. Do not reorder, filter, or copy it into
+  a second list.
+- `road_counts` must remain owned by `generate_scene.py`; fallback roads must
+  still leave it unchanged.
+- `Layer catalog warning:` print text must remain unchanged because it is the
+  only runtime warning for JS/Python layer drift.
+- `Road_<layer_id>` and `OSM_Road_<way_id>` names affect parity digests.
+- `clip_polygon()` and `feature_in_bounds()` behavior must be reused exactly;
+  do not replace with new geometry logic.
+- Parity is mandatory because this is a pure refactor of bpy-layer scene
+  generation.