chore(task): archive 08-03-smooth-cesium-preview-vehicle-cruise

.trellis/tasks/archive/2026-08/08-03-smooth-cesium-preview-vehicle-cruise/report.md

@@ -0,0 +1,57 @@
+# Smooth Cesium preview vehicle cruise report
+
+## Root Cause
+
+The first preview-only optimization helped but did not address the main load.
+User testing showed Follow still stuttered in scrub-heavy areas, while disabling
+`Scene` improved smoothness substantially.
+
+Current nantaizi GLB before the scrub-density change:
+
+- GLB nodes: `1271`
+- Scrub bush nodes: `707`
+- Scrub polygons: `5`
+
+The route data is small (`9` route segments, preview uses at most `5` vehicles),
+so route interpolation is not the primary bottleneck.
+
+## Changes
+
+- `scripts/lib/cesium-preview.js`
+  - Route helper polyline is now opaque instead of alpha blended.
+  - Route helper polyline uses `arcType: Cesium.ArcType.NONE`.
+  - Vehicle orientation and chase-follow camera callbacks reuse scratch
+    `JulianDate`, `HeadingPitchRoll`, `Quaternion`, and `Matrix4` objects.
+  - Default Cesium resolution and antialiasing are preserved; no blurry
+    performance mode is enabled by default.
+- `blender/generate_scene.py`
+  - `SCRUB_BUSH_SPACING`: `0.82 -> 1.8`
+  - `SCRUB_BUSH_LIMIT_PER_PATCH`: `180 -> 60`
+  - Scrub ground cover remains unchanged.
+
+## Validation
+
+Commands run:
+
+```bash
+node --check scripts/lib/cesium-preview.js
+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-after-scrub-glb-digest.json
+```
+
+Results after rebuild:
+
+- `SCENE_DONE` reports `scrub_bushes: 266`.
+- GLB nodes: `830`
+- Scrub bush nodes: `266`
+- Scrub polygons in metadata: `5`
+- Route segments in preview route JSON: `9`
+- GLB size: about `31.96 MB`
+
+## Deferred
+
+If Follow still stutters after this density reduction, the next root-level work
+should target the bush asset itself: lower-poly bush mesh, explicit LOD, or a
+proper instancing path supported by Cesium/glTF.