An animation reaches the scene's own background and objects inside placed containers (#109)

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/runtime/World.ts

@@ -1,6 +1,7 @@
 import { ENTITY_HANDLE, isHandleEnabled, type PointerState, worldMatrixOf } from '../core/graph';
 import { newId } from '../core/ids';
 import type { Asset } from '../core/model/Asset';
+import type { PropertyBag } from '../core/model/Properties';
 import { isPlaceableType } from '../core/model/AssetTypes';
 import { bakeInstances, materializeInstance, objectRef, resolveObjects } from '../core/model/instance';
 import { treeOrder } from '../core/model/hierarchy';
@@ -34,7 +35,8 @@ export interface ModelWrite {
  */
 export class World {
   readonly entities: Entity[] = [];
-  backgroundColor = 0x000000;
+  /** The running scene's own properties – read from the model, and written by an animation over the scene. */
+  readonly sceneProps: PropertyBag = {};
   /** Set by a behavior (Stop game node); the editor leaves play mode on the next tick. */
   stopRequested = false;
   /** Set by a behavior (Restart game node); the editor restarts the scene on the next tick. */
@@ -83,6 +85,11 @@ export class World {
     return this.elapsed;
   }
 
+  get backgroundColor(): number {
+    const background = this.sceneProps.backgroundColor;
+    return typeof background === 'number' ? background : 0x000000;
+  }
+
   /** Makes the entities match the scene; props are updated in place so systems holding a bag stay current. */
   syncFromModel(): void {
     const scene = findScene(this.project, this.sceneId);
@@ -91,8 +98,7 @@ export class World {
     // behavior destroy one of them for good. Play does it (on its throwaway copy); the editor run
     // must not, so there the content stays resolved and `objectRef` writes into the instance edits.
     if (this.bakeContainers && bakeInstances(this.project, scene)) this.structureChanged = true;
-    const background = scene.props.backgroundColor;
-    this.backgroundColor = typeof background === 'number' ? background : 0x000000;
+    Object.assign(this.sceneProps, scene.props);
     const objects = new Map(resolveObjects(this.project, scene).map((o) => [o.id, o]));
     const keep = new Set<Entity>();
     for (const object of objects.values()) {