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

AGENTS.md

@@ -119,6 +119,19 @@ These defaults are intentionally fixed for the early slices unless a later slice
 - placed imported models are **model instances**, not typed entities
 - keep model instances in a document collection separate from `entities`
 
+### Imported model collision scope
+
+- collision authoring for imported models belongs on `modelInstances`, not on asset records
+- the canonical source of truth is authored collision settings, not cooked collider bytes
+- generated collider data may be cached or rebuilt, but it is derived from:
+  - imported model asset geometry
+  - model instance transform
+  - authored collision settings
+- for imported-model collider support beyond simple boxes, prefer integrating a real collision/query library such as Rapier over inventing custom broad-phase/narrow-phase code in-house
+- let the collision/query layer own broad-phase and narrow-phase pruning instead of re-implementing that manually in app code
+- do not turn this slice into a full physics sandbox or general rigidbody architecture rewrite unless the roadmap explicitly asks for that
+- near-term slices may adapt or replace the current handcrafted runner collision path where necessary so brush and imported-model colliders can participate in one coherent collision/query system
+
 ### Runtime interaction scope
 
 - keep trigger/action/target links explicit and typed
@@ -161,6 +174,7 @@ Use these terms consistently:
 - **Texture**: image resource backing material channels
 - **Asset**: imported external resource, usually GLB/GLTF or audio and related media
 - **Model Instance**: placed scene instance of an imported asset
+- **Collider**: runtime collision representation derived from brushes or imported models
 - **Prefab**: reusable asset/entity package placeable in scenes
 - **Entity**: typed scene object with runtime/editor semantics
 - **Project Package**: portable editable bundle containing canonical scene JSON plus referenced assets
@@ -168,7 +182,7 @@ Use these terms consistently:
 - **Runner**: browser runtime that loads and plays scenes
 - **Viewport**: editor rendering surface
 - **Command**: undoable state transition
-- **Tool**: editor interaction mode such as select, move, box-create, face-edit
+- **Tool**: editor interaction mode such as select, create, transform, or face-edit
 - **Build**: deterministic transformation from document -> runtime scene data
 - **Export**: downstream transformation to deployable or interchange deliverables such as runner packages or optional later GLB
 
@@ -315,6 +329,21 @@ Do not store raw three.js objects inside canonical document state.
 - entity validation must happen at document/build boundaries
 - model instances remain separate from entities
 
+### Imported model collision rules
+
+- collision settings for imported models live on `modelInstances`
+- supported collision modes must be explicit and typed
+- generated collision geometry is derived data, not the canonical source document
+- collision debug visibility is editor/runtime UI state driven by authored settings, not a hidden renderer-only toggle
+- avoid implicit “always collide with render mesh” behavior
+- if broad-phase/narrow-phase pruning or non-box collider support is needed, prefer Rapier over ad hoc custom collision math
+- collision modes mean:
+  - `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
+
 ---
 
 ## Performance rules

CHAT_CONTEXT.md

@@ -113,6 +113,10 @@ Per face, keep explicit UV transform values such as:
 - imported assets live in the asset registry
 - placed imported models live in `modelInstances`
 - typed scene objects like `PlayerStart`, `TriggerVolume`, or lights live in `entities`
+- collision authoring for imported models belongs on `modelInstances`, not asset records
+- generated imported-model collider data should be derived from asset geometry + instance transform + authored settings
+- for imported-model collider types beyond simple boxes, prefer a Rapier-backed collision/query layer over extending the handcrafted collision code indefinitely
+- broad-phase and narrow-phase pruning should come from that collision/query layer, not custom app code
 
 ### Interaction scope
 

architecture.md

@@ -167,6 +167,21 @@ Placed imported models are not typed entities.
 - placed scene instances of those assets live in `modelInstances`
 - typed runtime/editor objects such as `PlayerStart` or `TriggerVolume` live in `entities`
 
+### Imported model collision scope
+
+Imported model collision should extend the current architecture, not replace it.
+
+- authored collision settings belong on `modelInstances`
+- generated collider data is derived from:
+  - imported model asset geometry
+  - model instance transform
+  - authored collision settings
+- do not make cooked/generated collider bytes the canonical source document by default
+- for non-box imported-model collider support and broad-phase/narrow-phase pruning, prefer integrating Rapier as a collision/query subsystem over inventing custom collision code in-house
+- broad-phase and narrow-phase pair pruning should be delegated to that collision/query layer rather than re-implemented manually in app code
+- do not turn this into a full general-purpose physics sandbox unless the product actually needs one
+- near-term slices may adapt or replace the current handcrafted runner collision path so brushes and imported models can participate in one coherent collision/query system
+
 ### Trigger/action/target scope
 
 Keep interaction links explicit and typed.
@@ -344,6 +359,8 @@ interface SceneDocument {
 }
 ```
 
+Imported model collision settings should be represented canonically on the relevant `ModelInstance` records or a tightly related typed sub-structure, not as hidden renderer/runtime state.
+
 `WorldSettings` is the correct home for:
 
 - background mode and background color/gradient
@@ -525,6 +542,14 @@ Responsibilities:
 - `AnimationSystem`
 - `RuntimeUIBridge`
 
+### Collision strategy progression
+
+Near-term runtime collision is intentionally narrower than a full game-engine physics stack.
+
+- early runner slices use deterministic explicit collision data for navigation and authored interactions
+- imported model collision should first plug into that same runtime build/query path
+- only introduce a broader physics world when dynamic rigid bodies, richer contact response, or other product requirements make it necessary
+
 ### Navigation modes
 
 Initial modes:
@@ -697,6 +722,59 @@ There should be a clear distinction between:
 - model instance
 - prefab definition
 
+### Imported model collision authoring
+
+Imported models need an explicit authored collision path that coexists with brush collision.
+
+Recommended authored settings shape:
+
+```ts
+type ModelInstanceCollisionMode =
+  | "none"
+  | "terrain"
+  | "static"
+  | "dynamic"
+  | "simple";
+
+interface ModelInstanceCollisionSettings {
+  mode: ModelInstanceCollisionMode;
+  visible: boolean;
+  simpleShape?: "box" | "sphere" | "capsule" | "convexHull";
+  terrainResolution?: number;
+  dynamicQuality?: "low" | "medium" | "high";
+}
+```
+
+Rules:
+
+- these settings are canonical authoring data
+- generated collider geometry is derived/cacheable data
+- collision generation is triggered by authored settings, not hidden import-time guesses
+- `modelInstances` remain separate from `entities`
+- collision debug rendering should be visually inspectable in editor and runner when enabled
+- preferred implementation path is:
+  - Rapier 3D WASM provides the collision/query layer
+  - Rapier owns broad-phase and narrow-phase pruning
+  - the editor document owns authored collider settings
+  - generated collider geometry/handles are derived runtime/cache data
+- collision modes should mean exactly:
+  - `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
+- initial support may be staged, but unsupported modes must fail clearly instead of silently degrading to random approximations
+
+### Collision strategy progression
+
+- early slices used handcrafted box-based player collision because only brush boxes existed
+- once imported-model colliders require terrain, trimesh, convex hull, or compound collision, the preferred next step is a Rapier-backed collision/query layer
+- this does not require a full gameplay physics sandbox in the same slice
+- a valid intermediate state is:
+  - fixed/queryable colliders for brushes and imported models
+  - existing first-person movement adapted to query against Rapier-backed colliders
+  - dynamic collider generation represented canonically even if full rigidbody simulation lands later
+
 ---
 
 ## `serialization`
@@ -905,11 +983,19 @@ SceneDocument
 -> validate
 -> resolve assets/materials/entities/model instances
 -> build brush meshes
+-> build model-instance collider data
 -> build colliders
 -> build runtime entity graph
 -> assemble runtime scene package
 ```
 
+In the near-term architecture, `build colliders` may include a mix of:
+
+- brush-derived colliders
+- imported-model-instance-derived colliders
+
+without requiring a full general-purpose physics world.
+
 ### Project package build stages
 
 ```txt

package.json

@@ -17,6 +17,7 @@
     "test:e2e": "playwright test"
   },
   "dependencies": {
+    "@dimforge/rapier3d-compat": "^0.19.3",
     "postprocessing": "^6.39.0",
     "react": "^18.3.1",
     "react-dom": "^18.3.1",

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

prompts.txt

@@ -698,6 +698,100 @@ Please implement fully and report:
 
 ---
 
+## Prompt 8B — Imported model collider authoring
+
+```text
+You are implementing Slice 3.1B — Imported model collider authoring.
+
+Read and follow:
+- AGENTS.md
+- CHAT_CONTEXT.md
+- architecture.md
+- roadmap.md
+- testing.md
+
+Before coding:
+- Inspect the current repo and extend the existing implementation.
+- Build on the existing model asset / model instance path. Do not merge model instances into entities.
+- Integrate with the existing runtime scene build, but use Rapier 3D WASM as the collision/query layer for this slice instead of inventing custom broad-phase/narrow-phase logic.
+- Do not turn this slice into a full gameplay-physics sandbox or broad entity rigidbody rewrite.
+- If you change persisted schema, update versioning, migrations, and at least one compatibility test.
+
+Current goal:
+Make imported model instances participate in collision by adding explicit authored collider settings, generated collider data, Rapier-backed collision/query integration, and runtime/debug support that fits the current codebase.
+
+Requirements:
+- Add canonical collision settings to model instances.
+- Add an inspector UI for imported model instances with an explicit collision mode selector:
+  - none
+  - terrain
+  - static
+  - dynamic
+  - simple
+- Add a collision visibility/debug toggle for model instances.
+- Generated collider data must be derived from:
+  - imported model asset geometry
+  - model instance transform
+  - authored collision settings
+- Keep the authored settings canonical. Do not make cooked/generated collider bytes the source of truth in the document.
+- If you add caching, keep it explicit and derived.
+- Use Rapier 3D WASM for broad-phase/narrow-phase pruning and collision/query evaluation in this slice.
+
+Collision-mode expectations:
+- `none`:
+  - no collider
+- `terrain`:
+  - heightfield collider
+  - static only
+  - if the source mesh cannot support the chosen terrain path cleanly, fail clearly with diagnostics instead of silently pretending it worked
+- `static`:
+  - triangle mesh collider
+  - fixed only
+- `dynamic`:
+  - convex decomposition into a compound collider
+  - dynamic/kinematic capable representation
+  - this slice does not require a full general rigidbody gameplay system, but the generated representation must be explicit and correct
+  - if actual runtime behavior is limited in this slice, document exactly what works now
+- `simple`:
+  - one cheap primitive or one convex hull
+  - keep the initial option set small and explicit if needed
+
+Runtime/build requirements:
+- Extend runtime scene build so imported model colliders participate in one coherent Rapier-backed collision/query path together with brush-authored world collision.
+- Broad-phase and narrow-phase handling should come from Rapier, not app-specific custom collision pruning code.
+- Keep first-person traversal/collision working. It is acceptable to adapt the current player collision path to query against Rapier-backed colliders instead of the handwritten box-only collision path.
+- Add debug visualization for generated imported-model collision in editor and/or runner when the visibility toggle is enabled.
+- Keep the implementation understandable and explicit.
+
+Important:
+- Do not build a giant general-purpose physics framework around Rapier in this slice.
+- Do not add arbitrary rigidbody components to every scene object just because Rapier is present.
+- Do not hide collider generation behind import-time magic; it should be driven by authored collision settings.
+- Do not treat the render mesh as automatically equal to the collision mesh in all modes.
+- Keep model-instance collision separate from brush collision and separate from typed entity schemas.
+
+Testing expectations:
+- Round-trip tests for model-instance collision settings
+- Migration/compatibility test if schema changes
+- Validation/build tests for invalid or unsupported collision-mode assumptions
+- Geometry/runtime tests for generated collider outputs where practical
+- Runtime/domain tests proving the generated colliders participate in the actual Rapier-backed collision/query path
+- Runner/domain tests proving imported-model collision works together with existing brush/world collision
+- Browser/e2e or manual verification for collision debug visibility if practical
+
+Please implement fully and report:
+- model-instance collision schema/settings
+- supported behavior for each collision mode
+- how generated collider data is represented and rebuilt/cached
+- how Rapier is integrated into the current runner collision/query architecture
+- how broad-phase/narrow-phase responsibilities are handled
+- how debug visibility works
+- tests added or updated
+- what limitations remain, especially for `terrain` and `dynamic`
+```
+
+---
+
 ## Prompt 9 — Animation playback
 
 ```text

roadmap.md

@@ -342,6 +342,40 @@ The tool becomes more than brush-only by supporting imported assets, authored li
 
 ---
 
+### Slice 3.1B — Imported model collider authoring
+
+#### Deliverables
+
+- canonical collision settings on model instances
+- explicit collision mode selector for:
+  - none
+  - terrain
+  - static
+  - dynamic
+  - simple
+- collision visibility/debug toggle
+- generated collider data derived from imported model geometry plus authored settings
+- Rapier-backed collision/query integration for imported-model colliders and broad-phase/narrow-phase handling
+- runtime build support for imported-model colliders in the runner collision path
+- editor/runner debug visualization of generated collision where enabled
+
+#### Acceptance criteria
+
+- author can choose a collision mode per model instance in the inspector
+- imported models can participate in runner collision without hand-authored invisible geometry
+- collider modes mean exactly:
+  - 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
+- generated collision survives save/load through canonical settings and deterministic rebuild behavior
+- broad-phase and narrow-phase pruning are handled by Rapier instead of app-specific custom collision code
+- the slice does not require a full gameplay-physics sandbox
+- unsupported or partial modes fail clearly instead of silently pretending to work
+
+---
+
 ### Slice 3.2 — Local lights and skyboxes
 
 #### Deliverables
@@ -593,6 +627,7 @@ A slice is complete only when:
 - per-face UV persistence
 - picking accuracy
 - collision generation from brush data
+- collision generation from imported model data
 - imported asset/material compatibility
 - browser audio unlock behavior
 - input edge cases across browsers

src/assets/model-instances.ts

@@ -2,6 +2,15 @@ import { createOpaqueId } from "../core/ids";
 import type { Vec3 } from "../core/vector";
 import type { ModelAssetRecord } from "./project-assets";
 
+export const MODEL_INSTANCE_COLLISION_MODES = ["none", "terrain", "static", "dynamic", "simple"] as const;
+
+export type ModelInstanceCollisionMode = (typeof MODEL_INSTANCE_COLLISION_MODES)[number];
+
+export interface ModelInstanceCollisionSettings {
+  mode: ModelInstanceCollisionMode;
+  visible: boolean;
+}
+
 export interface ModelInstance {
   id: string;
   kind: "modelInstance";
@@ -10,6 +19,7 @@ export interface ModelInstance {
   position: Vec3;
   rotationDegrees: Vec3;
   scale: Vec3;
+  collision: ModelInstanceCollisionSettings;
   animationClipName?: string;
   animationAutoplay?: boolean;
 }
@@ -32,6 +42,11 @@ export const DEFAULT_MODEL_INSTANCE_SCALE: Vec3 = {
   z: 1
 };
 
+export const DEFAULT_MODEL_INSTANCE_COLLISION_SETTINGS: ModelInstanceCollisionSettings = {
+  mode: "none",
+  visible: false
+};
+
 function cloneVec3(vector: Vec3): Vec3 {
   return {
     x: vector.x,
@@ -44,6 +59,39 @@ function areVec3Equal(left: Vec3, right: Vec3): boolean {
   return left.x === right.x && left.y === right.y && left.z === right.z;
 }
 
+export function isModelInstanceCollisionMode(value: unknown): value is ModelInstanceCollisionMode {
+  return MODEL_INSTANCE_COLLISION_MODES.includes(value as ModelInstanceCollisionMode);
+}
+
+export function createModelInstanceCollisionSettings(
+  overrides: Partial<ModelInstanceCollisionSettings> = {}
+): ModelInstanceCollisionSettings {
+  const mode = overrides.mode ?? DEFAULT_MODEL_INSTANCE_COLLISION_SETTINGS.mode;
+
+  if (!isModelInstanceCollisionMode(mode)) {
+    throw new Error("Model instance collision mode must be a supported value.");
+  }
+
+  const visible = overrides.visible ?? DEFAULT_MODEL_INSTANCE_COLLISION_SETTINGS.visible;
+
+  if (typeof visible !== "boolean") {
+    throw new Error("Model instance collision visibility must be a boolean.");
+  }
+
+  return {
+    mode,
+    visible
+  };
+}
+
+export function cloneModelInstanceCollisionSettings(settings: ModelInstanceCollisionSettings): ModelInstanceCollisionSettings {
+  return createModelInstanceCollisionSettings(settings);
+}
+
+export function areModelInstanceCollisionSettingsEqual(left: ModelInstanceCollisionSettings, right: ModelInstanceCollisionSettings): boolean {
+  return left.mode === right.mode && left.visible === right.visible;
+}
+
 export function normalizeModelInstanceName(name: string | null | undefined): string | undefined {
   if (name === undefined || name === null) {
     return undefined;
@@ -68,11 +116,15 @@ function assertPositiveFiniteVec3(vector: Vec3, label: string) {
 }
 
 export function createModelInstance(
-  overrides: Partial<Pick<ModelInstance, "id" | "name" | "position" | "rotationDegrees" | "scale" | "animationClipName" | "animationAutoplay">> & Pick<ModelInstance, "assetId">
+  overrides: Partial<
+    Pick<ModelInstance, "id" | "name" | "position" | "rotationDegrees" | "scale" | "collision" | "animationClipName" | "animationAutoplay">
+  > &
+    Pick<ModelInstance, "assetId">
 ): ModelInstance {
   const position = cloneVec3(overrides.position ?? DEFAULT_MODEL_INSTANCE_POSITION);
   const rotationDegrees = cloneVec3(overrides.rotationDegrees ?? DEFAULT_MODEL_INSTANCE_ROTATION_DEGREES);
   const scale = cloneVec3(overrides.scale ?? DEFAULT_MODEL_INSTANCE_SCALE);
+  const collision = cloneModelInstanceCollisionSettings(overrides.collision ?? DEFAULT_MODEL_INSTANCE_COLLISION_SETTINGS);
 
   if (overrides.assetId.trim().length === 0) {
     throw new Error("Model instance assetId must be a non-empty string.");
@@ -90,6 +142,7 @@ export function createModelInstance(
     position,
     rotationDegrees,
     scale,
+    collision,
     animationClipName: overrides.animationClipName,
     animationAutoplay: overrides.animationAutoplay
   };
@@ -128,6 +181,7 @@ export function areModelInstancesEqual(left: ModelInstance, right: ModelInstance
     areVec3Equal(left.position, right.position) &&
     areVec3Equal(left.rotationDegrees, right.rotationDegrees) &&
     areVec3Equal(left.scale, right.scale) &&
+    areModelInstanceCollisionSettingsEqual(left.collision, right.collision) &&
     left.animationClipName === right.animationClipName &&
     left.animationAutoplay === right.animationAutoplay
   );

src/document/migrate-scene-document.ts

@@ -1,7 +1,10 @@
 import { createStarterMaterialRegistry, type MaterialDef, type MaterialPattern } from "../materials/starter-material-library";
 import {
+  createModelInstanceCollisionSettings,
   createModelInstance,
+  isModelInstanceCollisionMode,
   normalizeModelInstanceName,
+  type ModelInstanceCollisionSettings,
   type ModelInstance
 } from "../assets/model-instances";
 import {
@@ -51,6 +54,7 @@ import {
   FACE_MATERIALS_SCENE_DOCUMENT_VERSION,
   FIRST_ROOM_POLISH_SCENE_DOCUMENT_VERSION,
   FOUNDATION_SCENE_DOCUMENT_VERSION,
+  IMPORTED_MODEL_COLLIDERS_SCENE_DOCUMENT_VERSION,
   LOCAL_LIGHTS_AND_SKYBOX_SCENE_DOCUMENT_VERSION,
   MODEL_ASSET_PIPELINE_SCENE_DOCUMENT_VERSION,
   RUNNER_V1_SCENE_DOCUMENT_VERSION,
@@ -503,6 +507,23 @@ function readAssets(value: unknown): SceneDocument["assets"] {
   return assets;
 }
 
+function readModelInstanceCollisionSettings(value: unknown, label: string): ModelInstanceCollisionSettings {
+  if (value === undefined) {
+    return createModelInstanceCollisionSettings();
+  }
+
+  if (!isRecord(value)) {
+    throw new Error(`${label} must be an object.`);
+  }
+
+  const mode = readOptionalAllowedValue(value.mode, `${label}.mode`, "none", isModelInstanceCollisionMode);
+
+  return createModelInstanceCollisionSettings({
+    mode,
+    visible: readOptionalBoolean(value.visible, `${label}.visible`, false)
+  });
+}
+
 function readModelInstance(value: unknown, label: string, assets: SceneDocument["assets"]): ModelInstance {
   if (!isRecord(value)) {
     throw new Error(`${label} must be an object.`);
@@ -526,6 +547,7 @@ function readModelInstance(value: unknown, label: string, assets: SceneDocument[
     position: readVec3(value.position, `${label}.position`),
     rotationDegrees: readVec3(value.rotationDegrees, `${label}.rotationDegrees`),
     scale: readVec3(value.scale, `${label}.scale`),
+    collision: readModelInstanceCollisionSettings(value.collision, `${label}.collision`),
     animationClipName: (() => {
       const raw = expectOptionalString(value.animationClipName, `${label}.animationClipName`);
       if (raw === undefined) return undefined;
@@ -1442,6 +1464,25 @@ export function migrateSceneDocument(source: unknown): SceneDocument {
     };
   }
 
+  // v15 -> v16: model instances gained authored collider settings.
+  if (source.version === ENTITY_NAMES_SCENE_DOCUMENT_VERSION) {
+    const materials = readMaterialRegistry(source.materials, "materials");
+    const assets = readAssets(source.assets);
+
+    return {
+      version: IMPORTED_MODEL_COLLIDERS_SCENE_DOCUMENT_VERSION,
+      name: expectString(source.name, "name"),
+      world: readWorldSettings(source.world),
+      materials,
+      textures: expectEmptyCollection(source.textures, "textures"),
+      assets,
+      brushes: readBrushes(source.brushes, materials, false),
+      modelInstances: readModelInstances(source.modelInstances, assets),
+      entities: readEntities(source.entities, { legacySoundEmitter: false }),
+      interactionLinks: readInteractionLinks(source.interactionLinks)
+    };
+  }
+
   // v14 -> v15: entities gained an optional authored name field.
   if (source.version === 14) {
     const materials = readMaterialRegistry(source.materials, "materials");

src/document/scene-document-validation.ts

@@ -6,6 +6,7 @@ import {
   type ProjectAssetRecord
 } from "../assets/project-assets";
 import type { ModelInstance } from "../assets/model-instances";
+import { isModelInstanceCollisionMode } from "../assets/model-instances";
 import {
   type InteractableEntity,
   type PointLightEntity,
@@ -646,6 +647,28 @@ function validateModelInstance(modelInstance: ModelInstance, path: string, docum
     diagnostics.push(createDiagnostic("error", "invalid-model-instance-scale", "Model instance scales must remain finite and positive on every axis.", `${path}.scale`));
   }
 
+  if (!isModelInstanceCollisionMode(modelInstance.collision.mode)) {
+    diagnostics.push(
+      createDiagnostic(
+        "error",
+        "invalid-model-instance-collision-mode",
+        "Model instance collision mode must be one of none, terrain, static, dynamic, or simple.",
+        `${path}.collision.mode`
+      )
+    );
+  }
+
+  if (!isBoolean(modelInstance.collision.visible)) {
+    diagnostics.push(
+      createDiagnostic(
+        "error",
+        "invalid-model-instance-collision-visibility",
+        "Model instance collision visibility must be a boolean.",
+        `${path}.collision.visible`
+      )
+    );
+  }
+
   const asset = document.assets[modelInstance.assetId];
 
   if (asset === undefined) {

src/document/scene-document.ts

@@ -6,7 +6,8 @@ import type { InteractionLink } from "../interactions/interaction-links";
 import { cloneMaterialRegistry, createStarterMaterialRegistry, type MaterialDef } from "../materials/starter-material-library";
 import { createDefaultWorldSettings, type WorldSettings } from "./world-settings";
 
-export const SCENE_DOCUMENT_VERSION = 15 as const;
+export const SCENE_DOCUMENT_VERSION = 16 as const;
+export const IMPORTED_MODEL_COLLIDERS_SCENE_DOCUMENT_VERSION = 16 as const;
 export const ENTITY_NAMES_SCENE_DOCUMENT_VERSION = 15 as const;
 export const SPATIAL_AUDIO_SCENE_DOCUMENT_VERSION = 13 as const;
 export const ANIMATION_PLAYBACK_SCENE_DOCUMENT_VERSION = 12 as const;

src/geometry/model-instance-collider-generation.ts

@@ -0,0 +1,677 @@
+import {
+  Euler,
+  Group,
+  MathUtils,
+  Matrix4,
+  Mesh,
+  Quaternion,
+  Vector3,
+  type BufferAttribute,
+  type BufferGeometry
+} from "three";
+
+import type { LoadedModelAsset } from "../assets/gltf-model-import";
+import type { ModelInstance, ModelInstanceCollisionMode } from "../assets/model-instances";
+import type { ModelAssetRecord } from "../assets/project-assets";
+import type { Vec3 } from "../core/vector";
+
+const TERRAIN_GRID_EPSILON = 1e-4;
+const DYNAMIC_TRIANGLE_TARGET = 48;
+const DYNAMIC_SPLIT_DEPTH_LIMIT = 3;
+
+interface LocalTriangle {
+  readonly a: Vector3;
+  readonly b: Vector3;
+  readonly c: Vector3;
+}
+
+interface LocalTriangleCluster {
+  readonly triangles: LocalTriangle[];
+}
+
+export interface GeneratedColliderBounds {
+  min: Vec3;
+  max: Vec3;
+}
+
+export interface GeneratedModelColliderTransform {
+  position: Vec3;
+  rotationDegrees: Vec3;
+  scale: Vec3;
+}
+
+interface GeneratedModelColliderBase {
+  source: "modelInstance";
+  instanceId: string;
+  assetId: string;
+  mode: ModelInstanceCollisionMode;
+  visible: boolean;
+  transform: GeneratedModelColliderTransform;
+  localBounds: GeneratedColliderBounds;
+  worldBounds: GeneratedColliderBounds;
+}
+
+export interface GeneratedModelBoxCollider extends GeneratedModelColliderBase {
+  kind: "box";
+  center: Vec3;
+  size: Vec3;
+}
+
+export interface GeneratedModelTriMeshCollider extends GeneratedModelColliderBase {
+  kind: "trimesh";
+  vertices: Float32Array;
+  indices: Uint32Array;
+  triangleCount: number;
+}
+
+export interface GeneratedModelHeightfieldCollider extends GeneratedModelColliderBase {
+  kind: "heightfield";
+  rows: number;
+  cols: number;
+  heights: Float32Array;
+  minX: number;
+  maxX: number;
+  minZ: number;
+  maxZ: number;
+}
+
+export interface GeneratedModelCompoundColliderPiece {
+  id: string;
+  points: Float32Array;
+  localBounds: GeneratedColliderBounds;
+}
+
+export interface GeneratedModelCompoundCollider extends GeneratedModelColliderBase {
+  kind: "compound";
+  pieces: GeneratedModelCompoundColliderPiece[];
+  decomposition: "spatial-bisect";
+  runtimeBehavior: "fixedQueryOnly";
+}
+
+export type GeneratedModelCollider =
+  | GeneratedModelBoxCollider
+  | GeneratedModelTriMeshCollider
+  | GeneratedModelHeightfieldCollider
+  | GeneratedModelCompoundCollider;
+
+export class ModelColliderGenerationError extends Error {
+  readonly code: string;
+
+  constructor(code: string, message: string) {
+    super(message);
+    this.name = "ModelColliderGenerationError";
+    this.code = code;
+  }
+}
+
+function cloneVec3(vector: Vec3): Vec3 {
+  return {
+    x: vector.x,
+    y: vector.y,
+    z: vector.z
+  };
+}
+
+function vector3ToVec3(vector: Vector3): Vec3 {
+  return {
+    x: vector.x,
+    y: vector.y,
+    z: vector.z
+  };
+}
+
+function createBounds(min: Vector3, max: Vector3): GeneratedColliderBounds {
+  return {
+    min: vector3ToVec3(min),
+    max: vector3ToVec3(max)
+  };
+}
+
+function createModelTransform(modelInstance: ModelInstance): GeneratedModelColliderTransform {
+  return {
+    position: cloneVec3(modelInstance.position),
+    rotationDegrees: cloneVec3(modelInstance.rotationDegrees),
+    scale: cloneVec3(modelInstance.scale)
+  };
+}
+
+function createModelTransformMatrix(modelInstance: ModelInstance): Matrix4 {
+  const rotation = new Euler(
+    MathUtils.degToRad(modelInstance.rotationDegrees.x),
+    MathUtils.degToRad(modelInstance.rotationDegrees.y),
+    MathUtils.degToRad(modelInstance.rotationDegrees.z),
+    "XYZ"
+  );
+  const quaternion = new Quaternion().setFromEuler(rotation);
+
+  return new Matrix4().compose(
+    new Vector3(modelInstance.position.x, modelInstance.position.y, modelInstance.position.z),
+    quaternion,
+    new Vector3(modelInstance.scale.x, modelInstance.scale.y, modelInstance.scale.z)
+  );
+}
+
+function computeBoundsFromPoints(points: Iterable<Vector3>): GeneratedColliderBounds {
+  const min = new Vector3(Number.POSITIVE_INFINITY, Number.POSITIVE_INFINITY, Number.POSITIVE_INFINITY);
+  const max = new Vector3(Number.NEGATIVE_INFINITY, Number.NEGATIVE_INFINITY, Number.NEGATIVE_INFINITY);
+  let hasPoint = false;
+
+  for (const point of points) {
+    hasPoint = true;
+    min.min(point);
+    max.max(point);
+  }
+
+  if (!hasPoint) {
+    throw new ModelColliderGenerationError("missing-model-collider-geometry", "The selected model does not contain any collision-capable geometry.");
+  }
+
+  return createBounds(min, max);
+}
+
+function computeBoundsFromFloat32Points(points: Float32Array): GeneratedColliderBounds {
+  if (points.length < 3) {
+    throw new ModelColliderGenerationError("missing-model-collider-geometry", "The selected model does not contain any collision-capable geometry.");
+  }
+
+  const min = new Vector3(Number.POSITIVE_INFINITY, Number.POSITIVE_INFINITY, Number.POSITIVE_INFINITY);
+  const max = new Vector3(Number.NEGATIVE_INFINITY, Number.NEGATIVE_INFINITY, Number.NEGATIVE_INFINITY);
+
+  for (let index = 0; index < points.length; index += 3) {
+    min.x = Math.min(min.x, points[index]);
+    min.y = Math.min(min.y, points[index + 1]);
+    min.z = Math.min(min.z, points[index + 2]);
+    max.x = Math.max(max.x, points[index]);
+    max.y = Math.max(max.y, points[index + 1]);
+    max.z = Math.max(max.z, points[index + 2]);
+  }
+
+  return createBounds(min, max);
+}
+
+function computeWorldBoundsFromLocalBox(localBounds: GeneratedColliderBounds, modelMatrix: Matrix4): GeneratedColliderBounds {
+  const min = localBounds.min;
+  const max = localBounds.max;
+  const corners = [
+    new Vector3(min.x, min.y, min.z),
+    new Vector3(min.x, min.y, max.z),
+    new Vector3(min.x, max.y, min.z),
+    new Vector3(min.x, max.y, max.z),
+    new Vector3(max.x, min.y, min.z),
+    new Vector3(max.x, min.y, max.z),
+    new Vector3(max.x, max.y, min.z),
+    new Vector3(max.x, max.y, max.z)
+  ];
+
+  return computeBoundsFromPoints(corners.map((corner) => corner.applyMatrix4(modelMatrix)));
+}
+
+function readIndexedVertex(position: BufferAttribute, index: number, matrix: Matrix4): Vector3 {
+  return new Vector3(position.getX(index), position.getY(index), position.getZ(index)).applyMatrix4(matrix);
+}
+
+function getMeshGeometry(object: Group | Mesh): BufferGeometry | null {
+  const maybeMesh = object as Mesh & { isMesh?: boolean };
+
+  if (maybeMesh.isMesh !== true) {
+    return null;
+  }
+
+  return maybeMesh.geometry;
+}
+
+function collectMeshTriangleClusters(template: Group): LocalTriangleCluster[] {
+  template.updateMatrixWorld(true);
+  const clusters: LocalTriangleCluster[] = [];
+
+  template.traverse((object) => {
+    const geometry = getMeshGeometry(object as Group | Mesh);
+
+    if (geometry === null) {
+      return;
+    }
+
+    const position = geometry.getAttribute("position");
+
+    if (position === undefined || position.itemSize < 3 || position.count < 3) {
+      return;
+    }
+
+    const matrix = object.matrixWorld;
+    const index = geometry.getIndex();
+    const triangles: LocalTriangle[] = [];
+
+    if (index === null) {
+      for (let vertexIndex = 0; vertexIndex <= position.count - 3; vertexIndex += 3) {
+        triangles.push({
+          a: readIndexedVertex(position, vertexIndex, matrix),
+          b: readIndexedVertex(position, vertexIndex + 1, matrix),
+          c: readIndexedVertex(position, vertexIndex + 2, matrix)
+        });
+      }
+    } else {
+      for (let triangleIndex = 0; triangleIndex <= index.count - 3; triangleIndex += 3) {
+        triangles.push({
+          a: readIndexedVertex(position, index.getX(triangleIndex), matrix),
+          b: readIndexedVertex(position, index.getX(triangleIndex + 1), matrix),
+          c: readIndexedVertex(position, index.getX(triangleIndex + 2), matrix)
+        });
+      }
+    }
+
+    if (triangles.length > 0) {
+      clusters.push({
+        triangles
+      });
+    }
+  });
+
+  return clusters;
+}
+
+function flattenTriangleClusters(clusters: LocalTriangleCluster[]): LocalTriangle[] {
+  return clusters.flatMap((cluster) => cluster.triangles);
+}
+
+function buildTriMeshBuffers(triangles: LocalTriangle[]): { vertices: Float32Array; indices: Uint32Array } {
+  const vertices = new Float32Array(triangles.length * 9);
+  const indices = new Uint32Array(triangles.length * 3);
+  let vertexOffset = 0;
+
+  for (let triangleIndex = 0; triangleIndex < triangles.length; triangleIndex += 1) {
+    const triangle = triangles[triangleIndex];
+    vertices[vertexOffset] = triangle.a.x;
+    vertices[vertexOffset + 1] = triangle.a.y;
+    vertices[vertexOffset + 2] = triangle.a.z;
+    vertices[vertexOffset + 3] = triangle.b.x;
+    vertices[vertexOffset + 4] = triangle.b.y;
+    vertices[vertexOffset + 5] = triangle.b.z;
+    vertices[vertexOffset + 6] = triangle.c.x;
+    vertices[vertexOffset + 7] = triangle.c.y;
+    vertices[vertexOffset + 8] = triangle.c.z;
+    indices[triangleIndex * 3] = triangleIndex * 3;
+    indices[triangleIndex * 3 + 1] = triangleIndex * 3 + 1;
+    indices[triangleIndex * 3 + 2] = triangleIndex * 3 + 2;
+    vertexOffset += 9;
+  }
+
+  return {
+    vertices,
+    indices
+  };
+}
+
+function computeClusterCentroid(triangles: LocalTriangle[]): Vec3 {
+  const centroid = {
+    x: 0,
+    y: 0,
+    z: 0
+  };
+  let pointCount = 0;
+
+  for (const triangle of triangles) {
+    centroid.x += triangle.a.x + triangle.b.x + triangle.c.x;
+    centroid.y += triangle.a.y + triangle.b.y + triangle.c.y;
+    centroid.z += triangle.a.z + triangle.b.z + triangle.c.z;
+    pointCount += 3;
+  }
+
+  return {
+    x: centroid.x / pointCount,
+    y: centroid.y / pointCount,
+    z: centroid.z / pointCount
+  };
+}
+
+function getTriangleBounds(triangles: LocalTriangle[]): GeneratedColliderBounds {
+  return computeBoundsFromPoints(triangles.flatMap((triangle) => [triangle.a, triangle.b, triangle.c]));
+}
+
+type TriangleClusterSplit =
+  | {
+      kind: "leaf";
+      triangles: LocalTriangle[];
+    }
+  | {
+      kind: "split";
+      left: LocalTriangle[];
+      right: LocalTriangle[];
+    };
+
+function splitTriangleCluster(triangles: LocalTriangle[], depth: number): TriangleClusterSplit {
+  if (triangles.length <= DYNAMIC_TRIANGLE_TARGET || depth >= DYNAMIC_SPLIT_DEPTH_LIMIT) {
+    return {
+      kind: "leaf",
+      triangles
+    };
+  }
+
+  const bounds = getTriangleBounds(triangles);
+  const size = {
+    x: bounds.max.x - bounds.min.x,
+    y: bounds.max.y - bounds.min.y,
+    z: bounds.max.z - bounds.min.z
+  };
+  const splitAxis = size.x >= size.y && size.x >= size.z ? "x" : size.y >= size.z ? "y" : "z";
+  const sortedTriangles = [...triangles].sort((left, right) => computeClusterCentroid([left])[splitAxis] - computeClusterCentroid([right])[splitAxis]);
+  const splitIndex = Math.floor(sortedTriangles.length * 0.5);
+
+  if (splitIndex <= 0 || splitIndex >= sortedTriangles.length) {
+    return {
+      kind: "leaf",
+      triangles
+    };
+  }
+
+  return {
+    kind: "split",
+    left: sortedTriangles.slice(0, splitIndex),
+    right: sortedTriangles.slice(splitIndex)
+  };
+}
+
+function collectConvexHullPointClouds(cluster: LocalTriangle[], depth = 0): Float32Array[] {
+  const split = splitTriangleCluster(cluster, depth);
+
+  if (split.kind === "leaf") {
+    return [dedupeTriangleClusterPoints(split.triangles)];
+  }
+
+  return [...collectConvexHullPointClouds(split.left, depth + 1), ...collectConvexHullPointClouds(split.right, depth + 1)];
+}
+
+function quantizeCoordinate(value: number): string {
+  return (Math.round(value / TERRAIN_GRID_EPSILON) * TERRAIN_GRID_EPSILON).toFixed(4);
+}
+
+function dedupeTriangleClusterPoints(triangles: LocalTriangle[]): Float32Array {
+  const pointLookup = new Map<string, Vec3>();
+
+  for (const triangle of triangles) {
+    for (const point of [triangle.a, triangle.b, triangle.c]) {
+      const key = `${quantizeCoordinate(point.x)}:${quantizeCoordinate(point.y)}:${quantizeCoordinate(point.z)}`;
+
+      if (!pointLookup.has(key)) {
+        pointLookup.set(key, {
+          x: point.x,
+          y: point.y,
+          z: point.z
+        });
+      }
+    }
+  }
+
+  if (pointLookup.size < 4) {
+    throw new ModelColliderGenerationError(
+      "unsupported-dynamic-model-collider",
+      "Dynamic collision requires volumetric geometry that can form at least one convex hull."
+    );
+  }
+
+  return new Float32Array(
+    Array.from(pointLookup.values()).flatMap((point) => [point.x, point.y, point.z])
+  );
+}
+
+function buildSimpleBoxCollider(modelInstance: ModelInstance, asset: ModelAssetRecord): GeneratedModelBoxCollider {
+  const boundingBox = asset.metadata.boundingBox;
+
+  if (boundingBox === null) {
+    throw new ModelColliderGenerationError(
+      "missing-model-collider-bounds",
+      `Model instance ${modelInstance.id} cannot use simple collision because the asset does not have a measurable bounding box.`
+    );
+  }
+
+  const localBounds = createBounds(
+    new Vector3(boundingBox.min.x, boundingBox.min.y, boundingBox.min.z),
+    new Vector3(boundingBox.max.x, boundingBox.max.y, boundingBox.max.z)
+  );
+
+  return {
+    source: "modelInstance",
+    instanceId: modelInstance.id,
+    assetId: modelInstance.assetId,
+    mode: "simple",
+    kind: "box",
+    visible: modelInstance.collision.visible,
+    transform: createModelTransform(modelInstance),
+    center: {
+      x: (boundingBox.min.x + boundingBox.max.x) * 0.5,
+      y: (boundingBox.min.y + boundingBox.max.y) * 0.5,
+      z: (boundingBox.min.z + boundingBox.max.z) * 0.5
+    },
+    size: cloneVec3(boundingBox.size),
+    localBounds,
+    worldBounds: computeWorldBoundsFromLocalBox(localBounds, createModelTransformMatrix(modelInstance))
+  };
+}
+
+function buildTriMeshCollider(modelInstance: ModelInstance, asset: ModelAssetRecord, loadedAsset: LoadedModelAsset | undefined): GeneratedModelTriMeshCollider {
+  if (loadedAsset === undefined) {
+    throw new ModelColliderGenerationError(
+      "missing-model-collider-geometry",
+      `Model instance ${modelInstance.id} cannot build ${modelInstance.collision.mode} collision until asset geometry has loaded.`
+    );
+  }
+
+  const triangles = flattenTriangleClusters(collectMeshTriangleClusters(loadedAsset.template));
+
+  if (triangles.length === 0) {
+    throw new ModelColliderGenerationError(
+      "missing-model-collider-geometry",
+      `Model instance ${modelInstance.id} cannot use ${modelInstance.collision.mode} collision because the asset has no mesh triangles.`
+    );
+  }
+
+  const buffers = buildTriMeshBuffers(triangles);
+  const localBounds = computeBoundsFromFloat32Points(buffers.vertices);
+
+  return {
+    source: "modelInstance",
+    instanceId: modelInstance.id,
+    assetId: asset.id,
+    mode: "static",
+    kind: "trimesh",
+    visible: modelInstance.collision.visible,
+    transform: createModelTransform(modelInstance),
+    vertices: buffers.vertices,
+    indices: buffers.indices,
+    triangleCount: triangles.length,
+    localBounds,
+    worldBounds: computeWorldBoundsFromLocalBox(localBounds, createModelTransformMatrix(modelInstance))
+  };
+}
+
+function buildTerrainCollider(
+  modelInstance: ModelInstance,
+  asset: ModelAssetRecord,
+  loadedAsset: LoadedModelAsset | undefined
+): GeneratedModelHeightfieldCollider {
+  if (loadedAsset === undefined) {
+    throw new ModelColliderGenerationError(
+      "missing-model-collider-geometry",
+      `Model instance ${modelInstance.id} cannot build terrain collision until asset geometry has loaded.`
+    );
+  }
+
+  const triangles = flattenTriangleClusters(collectMeshTriangleClusters(loadedAsset.template));
+
+  if (triangles.length === 0) {
+    throw new ModelColliderGenerationError(
+      "missing-model-collider-geometry",
+      `Model instance ${modelInstance.id} cannot use terrain collision because the asset has no mesh triangles.`
+    );
+  }
+
+  const heightLookup = new Map<string, { x: number; y: number; z: number }>();
+  const xValues = new Map<string, number>();
+  const zValues = new Map<string, number>();
+
+  for (const triangle of triangles) {
+    for (const point of [triangle.a, triangle.b, triangle.c]) {
+      const xKey = quantizeCoordinate(point.x);
+      const zKey = quantizeCoordinate(point.z);
+      const key = `${xKey}:${zKey}`;
+      const previousPoint = heightLookup.get(key);
+
+      if (previousPoint !== undefined && Math.abs(previousPoint.y - point.y) > TERRAIN_GRID_EPSILON) {
+        throw new ModelColliderGenerationError(
+          "unsupported-terrain-model-collider",
+          `Model instance ${modelInstance.id} cannot use terrain collision because the source mesh is not a single-valued heightfield over X/Z.`
+        );
+      }
+
+      heightLookup.set(key, {
+        x: point.x,
+        y: point.y,
+        z: point.z
+      });
+      xValues.set(xKey, point.x);
+      zValues.set(zKey, point.z);
+    }
+  }
+
+  const sortedX = Array.from(xValues.values()).sort((left, right) => left - right);
+  const sortedZ = Array.from(zValues.values()).sort((left, right) => left - right);
+
+  if (sortedX.length < 2 || sortedZ.length < 2) {
+    throw new ModelColliderGenerationError(
+      "unsupported-terrain-model-collider",
+      `Model instance ${modelInstance.id} cannot use terrain collision because the source mesh does not form a regular X/Z grid.`
+    );
+  }
+
+  const expectedTriangleCount = (sortedX.length - 1) * (sortedZ.length - 1) * 2;
+
+  if (triangles.length !== expectedTriangleCount) {
+    throw new ModelColliderGenerationError(
+      "unsupported-terrain-model-collider",
+      `Model instance ${modelInstance.id} cannot use terrain collision because the source mesh is not a clean regular-grid terrain surface.`
+    );
+  }
+
+  const heights = new Float32Array(sortedX.length * sortedZ.length);
+
+  for (let zIndex = 0; zIndex < sortedZ.length; zIndex += 1) {
+    for (let xIndex = 0; xIndex < sortedX.length; xIndex += 1) {
+      const key = `${quantizeCoordinate(sortedX[xIndex])}:${quantizeCoordinate(sortedZ[zIndex])}`;
+      const point = heightLookup.get(key);
+
+      if (point === undefined) {
+        throw new ModelColliderGenerationError(
+          "unsupported-terrain-model-collider",
+          `Model instance ${modelInstance.id} cannot use terrain collision because the source mesh is missing one or more regular-grid height samples.`
+        );
+      }
+
+      heights[xIndex + zIndex * sortedX.length] = point.y;
+    }
+  }
+
+  const localBounds = computeBoundsFromPoints(
+    Array.from(heightLookup.values(), (point) => new Vector3(point.x, point.y, point.z))
+  );
+
+  return {
+    source: "modelInstance",
+    instanceId: modelInstance.id,
+    assetId: asset.id,
+    mode: "terrain",
+    kind: "heightfield",
+    visible: modelInstance.collision.visible,
+    transform: createModelTransform(modelInstance),
+    rows: sortedX.length,
+    cols: sortedZ.length,
+    heights,
+    minX: sortedX[0],
+    maxX: sortedX.at(-1) ?? sortedX[0],
+    minZ: sortedZ[0],
+    maxZ: sortedZ.at(-1) ?? sortedZ[0],
+    localBounds,
+    worldBounds: computeWorldBoundsFromLocalBox(localBounds, createModelTransformMatrix(modelInstance))
+  };
+}
+
+function buildDynamicCollider(
+  modelInstance: ModelInstance,
+  asset: ModelAssetRecord,
+  loadedAsset: LoadedModelAsset | undefined
+): GeneratedModelCompoundCollider {
+  if (loadedAsset === undefined) {
+    throw new ModelColliderGenerationError(
+      "missing-model-collider-geometry",
+      `Model instance ${modelInstance.id} cannot build dynamic collision until asset geometry has loaded.`
+    );
+  }
+
+  const triangleClusters = collectMeshTriangleClusters(loadedAsset.template);
+
+  if (triangleClusters.length === 0) {
+    throw new ModelColliderGenerationError(
+      "missing-model-collider-geometry",
+      `Model instance ${modelInstance.id} cannot use dynamic collision because the asset has no mesh triangles.`
+    );
+  }
+
+  const pieces = triangleClusters
+    .flatMap((cluster) => collectConvexHullPointClouds(cluster.triangles))
+    .map((points, index) => ({
+      id: `${modelInstance.id}-piece-${index + 1}`,
+      points,
+      localBounds: computeBoundsFromFloat32Points(points)
+    }));
+
+  if (pieces.length === 0) {
+    throw new ModelColliderGenerationError(
+      "unsupported-dynamic-model-collider",
+      `Model instance ${modelInstance.id} could not derive any convex pieces for dynamic collision.`
+    );
+  }
+
+  const localBounds = computeBoundsFromPoints(
+    pieces.flatMap((piece) => {
+      const points: Vector3[] = [];
+
+      for (let pointIndex = 0; pointIndex < piece.points.length; pointIndex += 3) {
+        points.push(new Vector3(piece.points[pointIndex], piece.points[pointIndex + 1], piece.points[pointIndex + 2]));
+      }
+
+      return points;
+    })
+  );
+
+  return {
+    source: "modelInstance",
+    instanceId: modelInstance.id,
+    assetId: asset.id,
+    mode: "dynamic",
+    kind: "compound",
+    visible: modelInstance.collision.visible,
+    transform: createModelTransform(modelInstance),
+    pieces,
+    decomposition: "spatial-bisect",
+    runtimeBehavior: "fixedQueryOnly",
+    localBounds,
+    worldBounds: computeWorldBoundsFromLocalBox(localBounds, createModelTransformMatrix(modelInstance))
+  };
+}
+
+export function buildGeneratedModelCollider(
+  modelInstance: ModelInstance,
+  asset: ModelAssetRecord,
+  loadedAsset?: LoadedModelAsset
+): GeneratedModelCollider | null {
+  switch (modelInstance.collision.mode) {
+    case "none":
+      return null;
+    case "simple":
+      return buildSimpleBoxCollider(modelInstance, asset);
+    case "static":
+      return buildTriMeshCollider(modelInstance, asset, loadedAsset);
+    case "terrain":
+      return buildTerrainCollider(modelInstance, asset, loadedAsset);
+    case "dynamic":
+      return buildDynamicCollider(modelInstance, asset, loadedAsset);
+  }
+}

src/runtime-three/first-person-navigation-controller.ts

@@ -2,7 +2,7 @@ import { Euler, Vector3 } from "three";
 
 import type { Vec3 } from "../core/vector";
 
-import { FIRST_PERSON_PLAYER_SHAPE, resolveFirstPersonMotion } from "./player-collision";
+import { FIRST_PERSON_PLAYER_SHAPE } from "./player-collision";
 import type { NavigationController, RuntimeControllerContext } from "./navigation-controller";
 
 const LOOK_SENSITIVITY = 0.0022;
@@ -116,17 +116,22 @@ export class FirstPersonNavigationController implements NavigationController {
 
     this.verticalVelocity -= GRAVITY * dt;
 
-    const resolvedMotion = resolveFirstPersonMotion(
+    const resolvedMotion = this.context.resolveFirstPersonMotion(
       this.feetPosition,
       {
         x: horizontalX,
         y: this.verticalVelocity * dt,
         z: horizontalZ
       },
-      FIRST_PERSON_PLAYER_SHAPE,
-      this.context.getRuntimeScene().colliders
+      FIRST_PERSON_PLAYER_SHAPE
     );
 
+    if (resolvedMotion === null) {
+      this.updateCameraTransform();
+      this.publishTelemetry();
+      return;
+    }
+
     this.feetPosition = resolvedMotion.feetPosition;
     this.grounded = resolvedMotion.grounded;
 

src/runtime-three/navigation-controller.ts

@@ -2,6 +2,7 @@ import type { PerspectiveCamera } from "three";
 
 import type { Vec3 } from "../core/vector";
 
+import type { FirstPersonPlayerShape, ResolvedPlayerMotion } from "./player-collision";
 import type { RuntimeNavigationMode, RuntimeSceneDefinition, RuntimeSpawnPoint } from "./runtime-scene-build";
 
 export interface FirstPersonTelemetry {
@@ -16,6 +17,7 @@ export interface RuntimeControllerContext {
   camera: PerspectiveCamera;
   domElement: HTMLCanvasElement;
   getRuntimeScene(): RuntimeSceneDefinition;
+  resolveFirstPersonMotion(feetPosition: Vec3, motion: Vec3, shape: FirstPersonPlayerShape): ResolvedPlayerMotion | null;
   setRuntimeMessage(message: string | null): void;
   setFirstPersonTelemetry(telemetry: FirstPersonTelemetry | null): void;
 }

src/runtime-three/rapier-collision-world.ts

@@ -0,0 +1,278 @@
+import RAPIER from "@dimforge/rapier3d-compat";
+import { Euler, MathUtils, Quaternion, Vector3 } from "three";
+
+import type { Vec3 } from "../core/vector";
+import type {
+  GeneratedModelBoxCollider,
+  GeneratedModelCollider,
+  GeneratedModelCompoundCollider,
+  GeneratedModelHeightfieldCollider,
+  GeneratedModelTriMeshCollider
+} from "../geometry/model-instance-collider-generation";
+
+import type { FirstPersonPlayerShape, ResolvedPlayerMotion } from "./player-collision";
+import type { RuntimeBoxCollider, RuntimeSceneCollider } from "./runtime-scene-build";
+
+const CHARACTER_CONTROLLER_OFFSET = 0.01;
+const COLLISION_EPSILON = 1e-5;
+
+let rapierInitPromise: Promise<typeof RAPIER> | null = null;
+
+function cloneVec3(vector: Vec3): Vec3 {
+  return {
+    x: vector.x,
+    y: vector.y,
+    z: vector.z
+  };
+}
+
+function componentScale(vector: Vec3, scale: Vec3): Vec3 {
+  return {
+    x: vector.x * scale.x,
+    y: vector.y * scale.y,
+    z: vector.z * scale.z
+  };
+}
+
+function createRapierQuaternion(rotationDegrees: Vec3): RAPIER.Rotation {
+  const quaternion = new Quaternion().setFromEuler(
+    new Euler(
+      MathUtils.degToRad(rotationDegrees.x),
+      MathUtils.degToRad(rotationDegrees.y),
+      MathUtils.degToRad(rotationDegrees.z),
+      "XYZ"
+    )
+  );
+
+  return {
+    x: quaternion.x,
+    y: quaternion.y,
+    z: quaternion.z,
+    w: quaternion.w
+  };
+}
+
+function scaleVertices(vertices: Float32Array, scale: Vec3): Float32Array {
+  const scaledVertices = new Float32Array(vertices.length);
+
+  for (let index = 0; index < vertices.length; index += 3) {
+    scaledVertices[index] = vertices[index] * scale.x;
+    scaledVertices[index + 1] = vertices[index + 1] * scale.y;
+    scaledVertices[index + 2] = vertices[index + 2] * scale.z;
+  }
+
+  return scaledVertices;
+}
+
+function scaleBoundsCenter(bounds: { min: Vec3; max: Vec3 }, scale: Vec3): Vec3 {
+  return {
+    x: ((bounds.min.x + bounds.max.x) * 0.5) * scale.x,
+    y: ((bounds.min.y + bounds.max.y) * 0.5) * scale.y,
+    z: ((bounds.min.z + bounds.max.z) * 0.5) * scale.z
+  };
+}
+
+function createFixedBodyForModelCollider(world: RAPIER.World, collider: GeneratedModelCollider): RAPIER.RigidBody {
+  return world.createRigidBody(
+    RAPIER.RigidBodyDesc.fixed()
+      .setTranslation(collider.transform.position.x, collider.transform.position.y, collider.transform.position.z)
+      .setRotation(createRapierQuaternion(collider.transform.rotationDegrees))
+  );
+}
+
+function attachBrushCollider(world: RAPIER.World, collider: RuntimeBoxCollider) {
+  const center = {
+    x: (collider.min.x + collider.max.x) * 0.5,
+    y: (collider.min.y + collider.max.y) * 0.5,
+    z: (collider.min.z + collider.max.z) * 0.5
+  };
+  const halfExtents = {
+    x: (collider.max.x - collider.min.x) * 0.5,
+    y: (collider.max.y - collider.min.y) * 0.5,
+    z: (collider.max.z - collider.min.z) * 0.5
+  };
+
+  world.createCollider(RAPIER.ColliderDesc.cuboid(halfExtents.x, halfExtents.y, halfExtents.z).setTranslation(center.x, center.y, center.z));
+}
+
+function attachSimpleModelCollider(world: RAPIER.World, collider: GeneratedModelBoxCollider) {
+  const body = createFixedBodyForModelCollider(world, collider);
+  const scaledCenter = componentScale(collider.center, collider.transform.scale);
+  const scaledHalfExtents = componentScale(
+    {
+      x: collider.size.x * 0.5,
+      y: collider.size.y * 0.5,
+      z: collider.size.z * 0.5
+    },
+    collider.transform.scale
+  );
+
+  world.createCollider(
+    RAPIER.ColliderDesc.cuboid(scaledHalfExtents.x, scaledHalfExtents.y, scaledHalfExtents.z).setTranslation(
+      scaledCenter.x,
+      scaledCenter.y,
+      scaledCenter.z
+    ),
+    body
+  );
+}
+
+function attachStaticModelCollider(world: RAPIER.World, collider: GeneratedModelTriMeshCollider) {
+  const body = createFixedBodyForModelCollider(world, collider);
+  world.createCollider(RAPIER.ColliderDesc.trimesh(scaleVertices(collider.vertices, collider.transform.scale), collider.indices), body);
+}
+
+function attachTerrainModelCollider(world: RAPIER.World, collider: GeneratedModelHeightfieldCollider) {
+  const body = createFixedBodyForModelCollider(world, collider);
+  const center = scaleBoundsCenter(
+    {
+      min: {
+        x: collider.minX,
+        y: 0,
+        z: collider.minZ
+      },
+      max: {
+        x: collider.maxX,
+        y: 0,
+        z: collider.maxZ
+      }
+    },
+    collider.transform.scale
+  );
+
+  world.createCollider(
+    RAPIER.ColliderDesc.heightfield(collider.rows, collider.cols, collider.heights, {
+      x: (collider.maxX - collider.minX) * collider.transform.scale.x,
+      y: collider.transform.scale.y,
+      z: (collider.maxZ - collider.minZ) * collider.transform.scale.z
+    }).setTranslation(center.x, center.y, center.z),
+    body
+  );
+}
+
+function attachDynamicModelCollider(world: RAPIER.World, collider: GeneratedModelCompoundCollider) {
+  const body = createFixedBodyForModelCollider(world, collider);
+
+  for (const piece of collider.pieces) {
+    const scaledPoints = scaleVertices(piece.points, collider.transform.scale);
+    const descriptor = RAPIER.ColliderDesc.convexHull(scaledPoints);
+
+    if (descriptor === null) {
+      throw new Error(`Dynamic collider piece ${piece.id} could not form a valid convex hull.`);
+    }
+
+    world.createCollider(descriptor, body);
+  }
+}
+
+function attachModelCollider(world: RAPIER.World, collider: GeneratedModelCollider) {
+  switch (collider.kind) {
+    case "box":
+      attachSimpleModelCollider(world, collider);
+      break;
+    case "trimesh":
+      attachStaticModelCollider(world, collider);
+      break;
+    case "heightfield":
+      attachTerrainModelCollider(world, collider);
+      break;
+    case "compound":
+      attachDynamicModelCollider(world, collider);
+      break;
+  }
+}
+
+function feetPositionToColliderCenter(feetPosition: Vec3, shape: FirstPersonPlayerShape): Vec3 {
+  const cylindricalHalfHeight = Math.max(0, (shape.height - shape.radius * 2) * 0.5);
+
+  return {
+    x: feetPosition.x,
+    y: feetPosition.y + shape.radius + cylindricalHalfHeight,
+    z: feetPosition.z
+  };
+}
+
+function colliderCenterToFeetPosition(center: Vec3, shape: FirstPersonPlayerShape): Vec3 {
+  const cylindricalHalfHeight = Math.max(0, (shape.height - shape.radius * 2) * 0.5);
+
+  return {
+    x: center.x,
+    y: center.y - (shape.radius + cylindricalHalfHeight),
+    z: center.z
+  };
+}
+
+export async function initializeRapierCollisionWorld(): Promise<typeof RAPIER> {
+  rapierInitPromise ??= RAPIER.init().then(() => RAPIER);
+  return rapierInitPromise;
+}
+
+export class RapierCollisionWorld {
+  static async create(colliders: RuntimeSceneCollider[], playerShape: FirstPersonPlayerShape): Promise<RapierCollisionWorld> {
+    const rapier = await initializeRapierCollisionWorld();
+    const world = new rapier.World({
+      x: 0,
+      y: 0,
+      z: 0
+    });
+
+    for (const collider of colliders) {
+      if (collider.source === "brush") {
+        attachBrushCollider(world, collider);
+        continue;
+      }
+
+      attachModelCollider(world, collider);
+    }
+
+    const playerCollider = world.createCollider(
+      rapier.ColliderDesc.capsule(Math.max(0, (playerShape.height - playerShape.radius * 2) * 0.5), playerShape.radius)
+    );
+    const characterController = world.createCharacterController(CHARACTER_CONTROLLER_OFFSET);
+
+    characterController.setUp({ x: 0, y: 1, z: 0 });
+    characterController.setSlideEnabled(true);
+    characterController.enableSnapToGround(0.2);
+    characterController.enableAutostep(0.35, 0.15, false);
+    characterController.setMaxSlopeClimbAngle(Math.PI * 0.45);
+    characterController.setMinSlopeSlideAngle(Math.PI * 0.5);
+
+    return new RapierCollisionWorld(world, characterController, playerCollider);
+  }
+
+  private constructor(
+    private readonly world: RAPIER.World,
+    private readonly characterController: RAPIER.KinematicCharacterController,
+    private readonly playerCollider: RAPIER.Collider
+  ) {}
+
+  resolveFirstPersonMotion(feetPosition: Vec3, motion: Vec3, shape: FirstPersonPlayerShape): ResolvedPlayerMotion {
+    const currentCenter = feetPositionToColliderCenter(feetPosition, shape);
+    this.playerCollider.setTranslation(currentCenter);
+    this.characterController.computeColliderMovement(this.playerCollider, motion);
+
+    const correctedMovement = this.characterController.computedMovement();
+    const nextCenter = {
+      x: currentCenter.x + correctedMovement.x,
+      y: currentCenter.y + correctedMovement.y,
+      z: currentCenter.z + correctedMovement.z
+    };
+
+    this.playerCollider.setTranslation(nextCenter);
+
+    return {
+      feetPosition: colliderCenterToFeetPosition(nextCenter, shape),
+      grounded: this.characterController.computedGrounded(),
+      collidedAxes: {
+        x: Math.abs(correctedMovement.x - motion.x) > COLLISION_EPSILON,
+        y: Math.abs(correctedMovement.y - motion.y) > COLLISION_EPSILON,
+        z: Math.abs(correctedMovement.z - motion.z) > COLLISION_EPSILON
+      }
+    };
+  }
+
+  dispose() {
+    this.world.removeCharacterController(this.characterController);
+    this.world.free();
+  }
+}

src/runtime-three/runtime-host.ts

@@ -40,6 +40,8 @@ import {
 
 import { FirstPersonNavigationController } from "./first-person-navigation-controller";
 import type { FirstPersonTelemetry, NavigationController, RuntimeControllerContext } from "./navigation-controller";
+import { FIRST_PERSON_PLAYER_SHAPE } from "./player-collision";
+import { RapierCollisionWorld } from "./rapier-collision-world";
 import { RuntimeInteractionSystem, type RuntimeInteractionDispatcher, type RuntimeInteractionPrompt } from "./runtime-interaction-system";
 import { RuntimeAudioSystem } from "./runtime-audio-system";
 import { OrbitVisitorNavigationController } from "./orbit-visitor-navigation-controller";
@@ -85,6 +87,8 @@ export class RuntimeHost {
   private readonly controllerContext: RuntimeControllerContext;
   private readonly renderer: WebGLRenderer | null;
   private runtimeScene: RuntimeSceneDefinition | null = null;
+  private collisionWorld: RapierCollisionWorld | null = null;
+  private collisionWorldRequestId = 0;
   private currentWorld: RuntimeSceneDefinition["world"] | null = null;
   private currentAdvancedRenderingSettings: AdvancedRenderingSettings | null = null;
   private advancedRenderingComposer: EffectComposer | null = null;
@@ -131,6 +135,7 @@ export class RuntimeHost {
 
         return this.runtimeScene;
       },
+      resolveFirstPersonMotion: (feetPosition, motion, shape) => this.collisionWorld?.resolveFirstPersonMotion(feetPosition, motion, shape) ?? null,
       setRuntimeMessage: (message) => {
         if (message === this.currentRuntimeMessage) {
           return;
@@ -171,6 +176,7 @@ export class RuntimeHost {
     this.rebuildLocalLights(runtimeScene.localLights);
     this.rebuildBrushMeshes(runtimeScene.brushes);
     this.rebuildModelInstances(runtimeScene.modelInstances);
+    void this.rebuildCollisionWorld(runtimeScene.colliders);
     this.audioSystem.loadScene(runtimeScene);
   }
 
@@ -244,6 +250,8 @@ export class RuntimeHost {
     this.clearLocalLights();
     this.clearBrushMeshes();
     this.clearModelInstances();
+    this.collisionWorldRequestId += 1;
+    this.clearCollisionWorld();
     this.audioSystem.dispose();
     this.advancedRenderingComposer?.dispose();
     this.advancedRenderingComposer = null;
@@ -306,6 +314,36 @@ export class RuntimeHost {
     this.applyShadowState();
   }
 
+  private async rebuildCollisionWorld(colliders: RuntimeSceneDefinition["colliders"]) {
+    const requestId = ++this.collisionWorldRequestId;
+
+    this.clearCollisionWorld();
+
+    try {
+      const nextCollisionWorld = await RapierCollisionWorld.create(colliders, FIRST_PERSON_PLAYER_SHAPE);
+
+      if (requestId !== this.collisionWorldRequestId) {
+        nextCollisionWorld.dispose();
+        return;
+      }
+
+      this.collisionWorld = nextCollisionWorld;
+    } catch (error) {
+      if (requestId !== this.collisionWorldRequestId) {
+        return;
+      }
+
+      const message = error instanceof Error ? error.message : "Runner collision initialization failed.";
+      this.currentRuntimeMessage = `Runner collision initialization failed: ${message}`;
+      this.runtimeMessageHandler?.(this.currentRuntimeMessage);
+    }
+  }
+
+  private clearCollisionWorld() {
+    this.collisionWorld?.dispose();
+    this.collisionWorld = null;
+  }
+
   private syncAdvancedRenderingComposer(settings: AdvancedRenderingSettings) {
     if (this.renderer === null) {
       return;

src/runtime-three/runtime-scene-build.ts

@@ -1,3 +1,4 @@
+import type { LoadedModelAsset } from "../assets/gltf-model-import";
 import type { Vec3 } from "../core/vector";
 import { getModelInstances } from "../assets/model-instances";
 import type { BoxBrush, BoxFaceId, FaceUvState } from "../document/brushes";
@@ -5,6 +6,7 @@ import type { SceneDocument } from "../document/scene-document";
 import { cloneWorldSettings, type WorldSettings } from "../document/world-settings";
 import { getEntityInstances, getPrimaryPlayerStartEntity, type EntityInstance } from "../entities/entity-instances";
 import { getBoxBrushBounds } from "../geometry/box-brush";
+import { buildGeneratedModelCollider, type GeneratedColliderBounds, type GeneratedModelCollider } from "../geometry/model-instance-collider-generation";
 import { cloneInteractionLink, getInteractionLinks, type InteractionLink } from "../interactions/interaction-links";
 import { cloneMaterialDef, type MaterialDef } from "../materials/starter-material-library";
 import { cloneFaceUvState } from "../document/brushes";
@@ -28,11 +30,14 @@ export interface RuntimeBoxBrushInstance {
 
 export interface RuntimeBoxCollider {
   kind: "box";
+  source: "brush";
   brushId: string;
   min: Vec3;
   max: Vec3;
 }
 
+export type RuntimeSceneCollider = RuntimeBoxCollider | GeneratedModelCollider;
+
 export interface RuntimeSceneBounds {
   min: Vec3;
   max: Vec3;
@@ -132,7 +137,7 @@ export interface RuntimeSceneDefinition {
   world: WorldSettings;
   localLights: RuntimeLocalLightCollection;
   brushes: RuntimeBoxBrushInstance[];
-  colliders: RuntimeBoxCollider[];
+  colliders: RuntimeSceneCollider[];
   sceneBounds: RuntimeSceneBounds | null;
   modelInstances: RuntimeModelInstance[];
   entities: RuntimeEntityCollection;
@@ -143,6 +148,7 @@ export interface RuntimeSceneDefinition {
 
 interface BuildRuntimeSceneOptions {
   navigationMode?: RuntimeNavigationMode;
+  loadedModelAssets?: Record<string, LoadedModelAsset>;
 }
 
 function cloneVec3(vector: Vec3): Vec3 {
@@ -213,6 +219,7 @@ function buildRuntimeCollider(brush: BoxBrush): RuntimeBoxCollider {
 
   return {
     kind: "box",
+    source: "brush",
     brushId: brush.id,
     min: cloneVec3(bounds.min),
     max: cloneVec3(bounds.max)
@@ -232,21 +239,37 @@ function buildRuntimeModelInstance(modelInstance: SceneDocument["modelInstances"
   };
 }
 
-function combineColliderBounds(colliders: RuntimeBoxCollider[]): RuntimeSceneBounds | null {
+function getColliderBounds(collider: RuntimeSceneCollider): GeneratedColliderBounds {
+  if (collider.source === "brush") {
+    return {
+      min: cloneVec3(collider.min),
+      max: cloneVec3(collider.max)
+    };
+  }
+
+  return {
+    min: cloneVec3(collider.worldBounds.min),
+    max: cloneVec3(collider.worldBounds.max)
+  };
+}
+
+function combineColliderBounds(colliders: RuntimeSceneCollider[]): RuntimeSceneBounds | null {
   if (colliders.length === 0) {
     return null;
   }
 
-  const min = cloneVec3(colliders[0].min);
-  const max = cloneVec3(colliders[0].max);
+  const firstBounds = getColliderBounds(colliders[0]);
+  const min = cloneVec3(firstBounds.min);
+  const max = cloneVec3(firstBounds.max);
 
   for (const collider of colliders.slice(1)) {
-    min.x = Math.min(min.x, collider.min.x);
-    min.y = Math.min(min.y, collider.min.y);
-    min.z = Math.min(min.z, collider.min.z);
-    max.x = Math.max(max.x, collider.max.x);
-    max.y = Math.max(max.y, collider.max.y);
-    max.z = Math.max(max.z, collider.max.z);
+    const bounds = getColliderBounds(collider);
+    min.x = Math.min(min.x, bounds.min.x);
+    min.y = Math.min(min.y, bounds.min.y);
+    min.z = Math.min(min.z, bounds.min.z);
+    max.x = Math.max(max.x, bounds.max.x);
+    max.y = Math.max(max.y, bounds.max.y);
+    max.z = Math.max(max.z, bounds.max.z);
   }
 
   return {
@@ -396,15 +419,33 @@ function assertNever(value: never): never {
 }
 
 export function buildRuntimeSceneFromDocument(document: SceneDocument, options: BuildRuntimeSceneOptions = {}): RuntimeSceneDefinition {
-  assertRuntimeSceneBuildable(document, options.navigationMode ?? "orbitVisitor");
+  assertRuntimeSceneBuildable(document, {
+    navigationMode: options.navigationMode ?? "orbitVisitor",
+    loadedModelAssets: options.loadedModelAssets
+  });
 
   const brushes = Object.values(document.brushes).map((brush) => buildRuntimeBrush(brush, document));
-  const colliders = Object.values(document.brushes).map((brush) => buildRuntimeCollider(brush));
-  const sceneBounds = combineColliderBounds(colliders);
+  const colliders: RuntimeSceneCollider[] = Object.values(document.brushes).map((brush) => buildRuntimeCollider(brush));
   const modelInstances = getModelInstances(document.modelInstances).map(buildRuntimeModelInstance);
   const collections = buildRuntimeSceneCollections(document);
   const interactionLinks = getInteractionLinks(document.interactionLinks).map((link) => cloneInteractionLink(link));
   const playerStartEntity = getPrimaryPlayerStartEntity(document.entities);
+
+  for (const modelInstance of getModelInstances(document.modelInstances)) {
+    const asset = document.assets[modelInstance.assetId];
+
+    if (asset === undefined || asset.kind !== "model") {
+      continue;
+    }
+
+    const generatedCollider = buildGeneratedModelCollider(modelInstance, asset, options.loadedModelAssets?.[modelInstance.assetId]);
+
+    if (generatedCollider !== null) {
+      colliders.push(generatedCollider);
+    }
+  }
+
+  const combinedSceneBounds = combineColliderBounds(colliders);
   const playerStart =
     playerStartEntity === null
       ? null
@@ -419,14 +460,14 @@ export function buildRuntimeSceneFromDocument(document: SceneDocument, options:
     localLights: collections.localLights,
     brushes,
     colliders,
-    sceneBounds,
+    sceneBounds: combinedSceneBounds,
     modelInstances,
     entities: collections.entities,
     interactionLinks,
     playerStart,
     spawn:
       playerStart === null
-        ? buildFallbackSpawn(sceneBounds)
+        ? buildFallbackSpawn(combinedSceneBounds)
         : {
             source: "playerStart",
             entityId: playerStart.entityId,

src/runtime-three/runtime-scene-validation.ts

@@ -1,3 +1,5 @@
+import type { LoadedModelAsset } from "../assets/gltf-model-import";
+import { getModelInstances } from "../assets/model-instances";
 import type { SceneDocument } from "../document/scene-document";
 import {
   assertSceneDocumentIsValid,
@@ -6,6 +8,7 @@ import {
   type SceneDiagnostic
 } from "../document/scene-document-validation";
 import { getPrimaryPlayerStartEntity } from "../entities/entity-instances";
+import { buildGeneratedModelCollider, ModelColliderGenerationError } from "../geometry/model-instance-collider-generation";
 
 export interface RuntimeSceneBuildValidationResult {
   diagnostics: SceneDiagnostic[];
@@ -13,13 +16,18 @@ export interface RuntimeSceneBuildValidationResult {
   warnings: SceneDiagnostic[];
 }
 
+interface ValidateRuntimeSceneBuildOptions {
+  navigationMode: "firstPerson" | "orbitVisitor";
+  loadedModelAssets?: Record<string, LoadedModelAsset>;
+}
+
 export function validateRuntimeSceneBuild(
   document: SceneDocument,
-  navigationMode: "firstPerson" | "orbitVisitor"
+  options: ValidateRuntimeSceneBuildOptions
 ): RuntimeSceneBuildValidationResult {
   const diagnostics: SceneDiagnostic[] = [];
 
-  if (navigationMode === "firstPerson" && getPrimaryPlayerStartEntity(document.entities) === null) {
+  if (options.navigationMode === "firstPerson" && getPrimaryPlayerStartEntity(document.entities) === null) {
     diagnostics.push(
       createDiagnostic(
         "error",
@@ -31,6 +39,39 @@ export function validateRuntimeSceneBuild(
     );
   }
 
+  for (const modelInstance of getModelInstances(document.modelInstances)) {
+    const path = `modelInstances.${modelInstance.id}.collision.mode`;
+    const asset = document.assets[modelInstance.assetId];
+
+    if (modelInstance.collision.mode === "none" || asset === undefined || asset.kind !== "model") {
+      continue;
+    }
+
+    try {
+      const generatedCollider = buildGeneratedModelCollider(modelInstance, asset, options.loadedModelAssets?.[modelInstance.assetId]);
+
+      if (generatedCollider?.mode === "dynamic") {
+        diagnostics.push(
+          createDiagnostic(
+            "warning",
+            "dynamic-model-collider-fixed-query-only",
+            "Dynamic model collision currently generates convex compound pieces for Rapier queries, but the runner still uses them as fixed world collision rather than fully simulated rigid bodies.",
+            path,
+            "build"
+          )
+        );
+      }
+    } catch (error) {
+      const message = error instanceof Error ? error.message : "Imported model collision generation failed.";
+      const code =
+        error instanceof ModelColliderGenerationError
+          ? error.code
+          : "invalid-model-instance-collision-mode";
+
+      diagnostics.push(createDiagnostic("error", code, message, path, "build"));
+    }
+  }
+
   return {
     diagnostics,
     errors: diagnostics.filter((diagnostic) => diagnostic.severity === "error"),
@@ -38,10 +79,10 @@ export function validateRuntimeSceneBuild(
   };
 }
 
-export function assertRuntimeSceneBuildable(document: SceneDocument, navigationMode: "firstPerson" | "orbitVisitor") {
+export function assertRuntimeSceneBuildable(document: SceneDocument, options: ValidateRuntimeSceneBuildOptions) {
   assertSceneDocumentIsValid(document);
 
-  const validation = validateRuntimeSceneBuild(document, navigationMode);
+  const validation = validateRuntimeSceneBuild(document, options);
 
   if (validation.errors.length > 0) {
     throw new Error(`Runtime build is blocked: ${formatSceneDiagnosticSummary(validation.errors)}`);

src/viewport-three/viewport-host.ts

@@ -341,6 +341,7 @@ export class ViewportHost {
     this.renderer.domElement.addEventListener("pointerleave", this.handlePointerLeave);
     this.renderer.domElement.addEventListener("wheel", this.handleWheel, { passive: false });
     this.renderer.domElement.addEventListener("auxclick", this.handleAuxClick);
+    this.renderer.domElement.addEventListener("contextmenu", this.handleContextMenu);
     window.addEventListener("pointermove", this.handleWindowPointerMove);
     this.resize();
 
@@ -554,6 +555,7 @@ export class ViewportHost {
     this.renderer.domElement.removeEventListener("pointerleave", this.handlePointerLeave);
     this.renderer.domElement.removeEventListener("wheel", this.handleWheel);
     this.renderer.domElement.removeEventListener("auxclick", this.handleAuxClick);
+    this.renderer.domElement.removeEventListener("contextmenu", this.handleContextMenu);
     window.removeEventListener("pointermove", this.handleWindowPointerMove);
     this.clearLocalLights();
     this.clearBrushMeshes();
@@ -2289,6 +2291,16 @@ export class ViewportHost {
       return;
     }
 
+    if (event.button === 2) {
+      event.preventDefault();
+
+      if (this.currentTransformSession.kind === "active") {
+        this.transformCancelHandler?.();
+      }
+
+      return;
+    }
+
     if (event.button !== 0) {
       return;
     }
@@ -2657,11 +2669,15 @@ export class ViewportHost {
   };
 
   private handleAuxClick = (event: MouseEvent) => {
-    if (event.button === 1) {
+    if (event.button === 1 || event.button === 2) {
       event.preventDefault();
     }
   };
 
+  private handleContextMenu = (event: MouseEvent) => {
+    event.preventDefault();
+  };
+
   private findModelInstanceId(object: Object3D): string | null {
     let current: Object3D | null = object;
 

testing.md

@@ -37,10 +37,11 @@ Highest-priority confidence areas:
 4. per-face material/UV persistence
 5. runtime build correctness
 6. asset import survival
-7. project package portability once binary assets exist
-8. runner navigation/input reliability
-9. spatial audio and interaction basics
-10. critical regressions caught in CI
+7. imported-model collider generation and runtime collision correctness
+8. project package portability once binary assets exist
+9. runner navigation/input reliability
+10. spatial audio and interaction basics
+11. critical regressions caught in CI
 
 ---
 
@@ -158,6 +159,8 @@ Scope:
 - face generation
 - topology expectations
 - collision mesh generation
+- imported-model collider generation
+- Rapier-backed collider/query integration where relevant
 - UV projection generation
 - clipping results
 - derived mesh determinism
@@ -170,6 +173,13 @@ Examples:
 - clipping yields valid child brushes
 - generated geometry contains no NaNs
 - rebuild is deterministic for the same input
+- imported model collider generation produces finite valid data for the selected mode
+- imported-model collider generation honors the authored mode semantics:
+  - terrain -> heightfield
+  - static -> triangle mesh
+  - dynamic -> compound convex pieces
+  - simple -> primitive or convex hull
+- unsupported imported-model collision modes fail clearly instead of producing silent garbage
 
 ### Geometry test principles
 
@@ -212,6 +222,12 @@ For every substantial document feature, add at least:
 - one round-trip save/load test
 - one migration or backward-compatibility consideration if schema changed
 
+For authored imported-model collision settings, also add at least:
+
+- one round-trip test for the selected collision mode/settings
+- one validation/build-path test for missing asset or incompatible collision-mode assumptions where relevant
+- one runtime/query-path test proving the generated collider participates in the actual collision/query layer rather than only existing as dead metadata
+
 ---
 
 ## 5. Browser integration tests