auto-git:

[add] src/geometry/model-instance-collider-generation.ts
 [add] src/runtime-three/rapier-collision-world.ts
 [change] AGENTS.md
 [change] CHAT_CONTEXT.md
 [change] architecture.md
 [change] package.json
 [change] prompts-lite.txt
 [change] prompts.txt
 [change] roadmap.md
 [change] src/assets/model-instances.ts
 [change] src/document/migrate-scene-document.ts
 [change] src/document/scene-document-validation.ts
 [change] src/document/scene-document.ts
 [change] src/runtime-three/first-person-navigation-controller.ts
 [change] src/runtime-three/navigation-controller.ts
 [change] src/runtime-three/runtime-host.ts
 [change] src/runtime-three/runtime-scene-build.ts
 [change] src/runtime-three/runtime-scene-validation.ts
 [change] src/viewport-three/viewport-host.ts
 [change] testing.md

prompts-lite.txt

@@ -341,6 +341,46 @@ Do not:
 
 ---
 
+## Slice Body 8B — Imported model collider authoring
+
+```text
+Relevant docs to inspect after the common preamble:
+- architecture.md: model instances, assets, runtime build, collision scope
+- roadmap.md: Slice 3.1B
+- testing.md: serialization, geometry/runtime, collision coverage
+
+Implement Slice 3.1B.
+
+Requirements:
+- canonical collision settings on model instances
+- inspector selector for:
+  - none
+  - terrain
+  - static
+  - dynamic
+  - simple
+- collision visibility/debug toggle
+- generated collider data derived from model asset geometry + model instance transform + authored settings
+- Rapier-backed collision/query integration for broad-phase/narrow-phase handling
+- runtime integration with the existing runner collision path
+- debug visualization for generated collision where enabled
+- explicit collider semantics:
+  - none = no collider
+  - terrain = heightfield collider, static only
+  - static = triangle mesh collider, fixed only
+  - dynamic = convex decomposition into compound collider, dynamic/kinematic capable
+  - simple = one cheap primitive or one convex hull
+
+Constraints:
+- do not merge model instances into entities
+- use Rapier instead of inventing custom broad-phase/narrow-phase code
+- do not rewrite the runner into a full gameplay-physics sandbox in this slice
+- keep authored settings canonical and generated collider data derived/cacheable
+- if terrain/dynamic support is partial, fail clearly and document it
+```
+
+---
+
 ## Slice Body 9 — Animation playback
 
 ```text