Fix OSM multipolygon buildings

.trellis/tasks/08-03-fix-osm-multipolygon-buildings/check.jsonl

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+{"_example": "Fill with {\"file\": \"<path>\", \"reason\": \"<why>\"}. Put spec/research files only — no code paths. Run `python3 .trellis/scripts/get_context.py --mode packages` to list available specs. Delete this line once real entries are added."}

.trellis/tasks/08-03-fix-osm-multipolygon-buildings/implement.jsonl

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+{"_example": "Fill with {\"file\": \"<path>\", \"reason\": \"<why>\"}. Put spec/research files only — no code paths. Run `python3 .trellis/scripts/get_context.py --mode packages` to list available specs. Delete this line once real entries are added."}

.trellis/tasks/08-03-fix-osm-multipolygon-buildings/prd.md

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+# Fix OSM multipolygon building rendering
+
+## Goal
+
+Fix Blender scene generation so OSM `type=multipolygon` building relations are
+rendered as buildings, and explicit OSM `height` tags are respected for normal
+buildings.
+
+## Requirements
+
+1. Parse OSM multipolygon relations whose relation tags include `building=*`.
+2. Use relation-level tags, including `height`, when generating the building.
+3. Support the common case of closed outer way members and closed inner way
+   members, as seen in nantaizi `relation -65`.
+4. Keep existing way-based building rendering working.
+5. Change building height semantics so an explicit `height` tag controls render
+   height; fallback office default `11.4m` should apply only when height is not
+   explicitly present and the building is not industrial / tall.
+6. Validate only `nantaizi-lake-innovation-valley`.
+
+## Acceptance Criteria
+
+- [x] `parse_osm()` exposes the nantaizi building multipolygon relation as a
+      renderable building feature.
+- [x] Unit tests cover relation-level building tags, outer/inner members, and
+      malformed / incomplete relation members.
+- [x] Existing way-based building parsing tests still pass.
+- [x] A relation building with `height=8` renders at `8m`, not the office
+      fallback `11.4m`.
+- [x] nantaizi Blender generation succeeds and includes the multipolygon
+      building in counts / scene digest.
+- [x] No hanyang validation is required unless requested.
+
+## Notes
+
+- Concrete reproduction in current input:
+  `relation -65` has `building=yes`, `height=8`, `type=multipolygon`, outer way
+  `-2948`, and inner way `-2952`. The member ways carry no building tags, so the
+  current way-only dispatcher skips it.

.trellis/tasks/08-03-fix-osm-multipolygon-buildings/report.md

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+# Multipolygon building fix report
+
+## Root Cause
+
+The edited nantaizi OSM has `relation -65` with:
+
+- `type=multipolygon`
+- `building=yes`
+- `height=8`
+- outer way `-2948`
+- inner way `-2952`
+
+The member ways have no building tags. `parse_osm()` only exposed ways, and
+`generate_scene.py` only dispatched ways, so the relation was skipped.
+
+The height issue had a second cause: ordinary non-industrial buildings below
+`30m` were forced to the office fallback render height `11.4m`, even when OSM
+had an explicit `height`.
+
+## Implemented
+
+- `parse_osm()` now exposes building multipolygon relations as synthetic
+  building features with relation-level tags and `inner_coords`.
+- Open relation member way fragments can be stitched into closed rings; malformed
+  relation leftovers are skipped without aborting parsing.
+- `generate_scene.py` passes projected `inner_rings` to building assembly.
+- `building.py` creates prism and roof meshes with holes using Blender
+  tessellation.
+- Explicit OSM `height` now controls render height. The `11.4m` office fallback
+  applies only when height is not explicit.
+
+## Validation
+
+- `python3 -m unittest discover blender/tests`
+- `npm run build:area -- --config config/areas/nantaizi-lake-innovation-valley.json --stages blender`
+- `npm run build:area -- --config config/areas/nantaizi-lake-innovation-valley.json --stages cesium`
+- `node scripts/glb-digest.js outputs/nantaizi-lake-innovation-valley/nantaizi-lake-innovation-valley.glb`
+- `python3 ./.trellis/scripts/task.py validate .trellis/tasks/08-03-fix-osm-multipolygon-buildings`
+- `git diff --check`
+
+Confirmed `Building_-65` in scene and GLB:
+
+- `osm_height=8`
+- `render_height=8`
+- GLB contains `Building_-65`, `Building_-65_Roof`, and
+  `Building_-65_Windows`
+
+User verified the result visually in preview.

.trellis/tasks/08-03-fix-osm-multipolygon-buildings/task.json

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+{
+  "id": "fix-osm-multipolygon-buildings",
+  "name": "fix-osm-multipolygon-buildings",
+  "title": "Fix OSM multipolygon building rendering",
+  "description": "",
+  "status": "in_progress",
+  "dev_type": null,
+  "scope": null,
+  "package": null,
+  "priority": "P2",
+  "creator": "dingkang",
+  "assignee": "dingkang",
+  "createdAt": "2026-08-03",
+  "completedAt": null,
+  "branch": null,
+  "base_branch": "main",
+  "worktree_path": null,
+  "commit": null,
+  "pr_url": null,
+  "subtasks": [],
+  "children": [],
+  "parent": null,
+  "relatedFiles": [],
+  "notes": "",
+  "meta": {}
+}