Apply/revert buttons for overrides, container instances and child positions

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

src/core/model/container.ts

@@ -1,8 +1,47 @@
 import { newId } from '../ids';
-import type { ContainerAsset } from './Asset';
+import type { ContainerAsset, SceneAsset } from './Asset';
+import { findObject, type ObjectTree } from './hierarchy';
 import { findAsset, type Project } from './Project';
 import type { SceneObject } from './SceneObject';
 
+/** What a placed container's content object is linked to: the container and its template object. */
+export interface TemplateLink {
+  containerObject: SceneObject;
+  asset: ContainerAsset;
+  template: SceneObject;
+}
+
+/**
+ * For an object that belongs to a placed container: the nearest container ancestor whose
+ * asset holds the template this object was instantiated from. Undefined for everything else
+ * (no template id, or the link is stale).
+ */
+export function templateLinkOf(project: Project, tree: ObjectTree, object: SceneObject): TemplateLink | undefined {
+  if (!object.templateId) return undefined;
+  const seen = new Set<string>([object.id]);
+  let current = object.parentId ? findObject(tree, object.parentId) : undefined;
+  while (current && !seen.has(current.id)) {
+    const asset = findAsset(project, current.assetId);
+    if (asset?.type === 'container') {
+      const template = asset.objects.find((t) => t.id === object.templateId);
+      if (template) return { containerObject: current, asset, template };
+    }
+    seen.add(current.id);
+    current = current.parentId ? findObject(tree, current.parentId) : undefined;
+  }
+  return undefined;
+}
+
+/** Every placed copy of a template object, across all scenes (template ids are unique per project). */
+export function instancesOf(project: Project, templateId: string): { scene: SceneAsset; object: SceneObject }[] {
+  const result: { scene: SceneAsset; object: SceneObject }[] = [];
+  for (const asset of project.assets) {
+    if (asset.type !== 'scene') continue;
+    for (const object of asset.objects) if (object.templateId === templateId) result.push({ scene: asset, object });
+  }
+  return result;
+}
+
 /** Nesting depth at which a container inside a container inside … stops being expanded. */
 const MAX_NESTING = 8;