Spawn node: place assets at runtime into the play copy, Spawner demo behavior

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/core/graph/NodeRegistry.ts

@@ -62,6 +62,12 @@ export interface NodeContext {
    */
   moveAndSlide(target: EntityHandle, dx: number, dy: number): { blockedX: boolean; blockedY: boolean };
   log(message: string): void;
+  /**
+   * Places a new instance of an asset into the running scene and returns it. The position is
+   * local to `parent` (world when none). Returns null when the asset does not exist or cannot
+   * be placed (a scene). Spawned behaviors run their `On start` on the next tick.
+   */
+  spawn(assetId: string, position: { x: number; y: number; z: number }, parent: EntityHandle | null): EntityHandle | null;
   destroy(target: EntityHandle): void;
   stop(): void;
 }

src/core/graph/nodes.ts

@@ -346,6 +346,22 @@ registerNode({
     return { next: 'exec' };
   },
 });
+registerNode({
+  type: 'Spawn',
+  label: 'Spawn',
+  category: 'action',
+  description: 'Creates a new instance of an asset in the running scene at (x, y, z) – local to the parent when one is connected, world coordinates otherwise. Outputs the new object.',
+  inputs: [exec(), num('x'), num('y'), num('z'), obj('parent')],
+  outputs: [exec(), obj('object')],
+  // Placeholder options: the graph inspector lists the project's placeable assets.
+  params: [{ key: 'asset', label: 'Asset', kind: 'enum', default: '', options: [] }],
+  run: (ctx, i, p) => {
+    const assetId = String(p.asset ?? '');
+    const spawned = assetId ? ctx.spawn(assetId, { x: asNumber(i.x), y: asNumber(i.y), z: asNumber(i.z) }, asEntity(i.parent)) : null;
+    if (!spawned) ctx.log(assetId ? `Spawn: asset ${assetId} not found` : 'Spawn: no asset selected');
+    return { outputs: { object: spawned }, next: 'exec' };
+  },
+});
 registerNode({
   type: 'Log',
   label: 'Log',