fix: prevent crash when duplicating elements (#239)

- Guard _buildCache in merged-outline-node against stale/disposed
  Object3D refs that cause TypeError on .id access during render
- Reset children array when duplicating roofs to prevent inconsistent
  parent-child relationships (matching existing stair behavior)
- Use obj?.parent check in EditorOutlinerSync to ensure objects are
  still in the scene graph before adding to outliner arrays
- Resume temporal state on parse failure to prevent undo/redo freeze

Closes #232

packages/editor/src/components/editor/floating-action-menu.tsx

@@ -147,6 +147,7 @@ export function FloatingActionMenu() {
           duplicate.start = [duplicate.start[0] + 1, duplicate.start[1] + 1]
           duplicate.end = [duplicate.end[0] + 1, duplicate.end[1] + 1]
         } else if (node.type === 'roof') {
+          duplicateInfo.children = []
           duplicate = RoofNode.parse(duplicateInfo)
         } else if (node.type === 'roof-segment') {
           duplicate = RoofSegmentNode.parse(duplicateInfo)
@@ -160,6 +161,12 @@ export function FloatingActionMenu() {
         }
       } catch (error) {
         console.error('Failed to parse duplicate', error)
+        useScene.temporal.getState().resume()
+        return
+      }
+
+      if (!duplicate) {
+        useScene.temporal.getState().resume()
         return
       }
 

packages/editor/src/components/editor/selection-manager.tsx

@@ -920,13 +920,13 @@ const EditorOutlinerSync = () => {
     outliner.selectedObjects.length = 0
     for (const id of idsToHighlight) {
       const obj = sceneRegistry.nodes.get(id)
-      if (obj) outliner.selectedObjects.push(obj)
+      if (obj?.parent) outliner.selectedObjects.push(obj)
     }
 
     outliner.hoveredObjects.length = 0
     if (hoveredId) {
       const obj = sceneRegistry.nodes.get(hoveredId)
-      if (obj) outliner.hoveredObjects.push(obj)
+      if (obj?.parent) outliner.hoveredObjects.push(obj)
     }
   }, [phase, previewSelectedIds, selection, hoveredId, outliner])