chore(task): archive 08-03-use-low-poly-scrub-bush

.trellis/tasks/archive/2026-08/08-03-use-low-poly-scrub-bush/report.md

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+# Low-poly scrub bush experiment report
+
+## Outcome
+
+Do not adopt `assets/models/custom/bush_low/bush_low.glb` as the default scrub
+edge bush.
+
+The asset successfully reduced geometry cost, but user validation found the
+visual result unsatisfactory. The default generator was restored to
+`assets/models/custom/bush/bush.glb`.
+
+## Measurements
+
+Commands used during the experiment:
+
+```bash
+python3 -m py_compile blender/generate_scene.py
+python3 -m unittest blender/tests/test_pure.py
+npm run build:area -- --config config/areas/nantaizi-lake-innovation-valley.json --stages blender,cesium,preview
+node scripts/glb-digest.js outputs/nantaizi-lake-innovation-valley/nantaizi-lake-innovation-valley.glb --out /tmp/nantaizi-bush-low-glb-digest.json
+node scripts/glb-digest.js assets/models/custom/bush/bush.glb --out /tmp/bush-original-digest.json
+node scripts/glb-digest.js assets/models/custom/bush_low/bush_low.glb --out /tmp/bush-low-asset-digest.json
+```
+
+Low-poly asset geometry:
+
+- Original `bush.glb`: `9.10 MB`, `63,762` vertices, `67,536` indices.
+- Experimental `bush_low.glb`: `5.79 MB`, `4,044` vertices, `4,050` indices.
+- Texture count stayed at `6`, so file size did not fall proportionally with
+  geometry.
+
+Nantaizi rebuild while using `bush_low.glb`:
+
+- `SCENE_DONE.scrub_bushes`: `266`
+- GLB nodes: `830`
+- Scrub bush nodes: `266`
+- Scrub bush shared mesh: `4,044` vertices, `4,050` indices
+- GLB size: `27.51 MB`
+- Metadata scrub polygons: `5`
+
+## Decision
+
+This proved geometry reduction works, but this particular low-poly model is not
+good enough visually. Keep the current density budget and original default bush
+asset for now. The next useful direction is a better-authored low-poly bush:
+same approximate silhouette/volume as the original, lower geometry, and reduced
+or compressed texture payload.