fix(builder): deep-clone node data on id regeneration to avoid shared props

regenerateTreeIds shallow-copied each node's data, leaving data.props (and
data.custom) as the same object reference between the original node and its
duplicate/pasted copy. Craft.js's setProp mutates data.props in place, so
editing the duplicate's props silently mutated the original too. Deep-clone
data via structuredClone before applying id remaps so no mutable sub-object
is shared between original and regenerated nodes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

craft/src/utils/craft-tree.test.ts

@@ -129,4 +129,21 @@ describe('regenerateTreeIds', () => {
     regenerateTreeIds(input);
     expect(JSON.parse(JSON.stringify(input))).toEqual(snapshot);
   });
+
+  test('output node data.props is a deep clone, not shared with the input node', () => {
+    const input = makeTree();
+    input.nodes['root-1'].data.props = { alignment: 'left' };
+
+    const output = regenerateTreeIds(input);
+    const outputRoot = output.nodes[output.rootNodeId];
+
+    // Clone must preserve content at the time of cloning.
+    expect(outputRoot.data.props).toEqual({ alignment: 'left' });
+
+    // Mutating the output's props (simulating Craft.js's in-place setProp)
+    // must NOT affect the input node's props object.
+    (outputRoot.data.props as { alignment: string }).alignment = 'right';
+
+    expect(input.nodes['root-1'].data.props).toEqual({ alignment: 'left' });
+  });
 });

craft/src/utils/craft-tree.ts

@@ -43,11 +43,18 @@ export function regenerateTreeIds(tree: NodeTree): NodeTree {
       newLinkedNodes[slot] = remapId(linkedId);
     }
 
+    // Deep-clone data so mutable sub-objects (props, custom, etc.) are never
+    // shared by reference between the original node and its regenerated
+    // copy. Craft.js's setProp mutates data.props in place, so a shallow
+    // copy here would let edits to the duplicate silently corrupt the
+    // original.
+    const clonedData = structuredClone(oldNode.data);
+
     const newNode: Node = {
       ...oldNode,
       id: newId,
       data: {
-        ...oldNode.data,
+        ...clonedData,
         parent: newParent,
         nodes: (oldNode.data.nodes || []).map(remapId),
         linkedNodes: newLinkedNodes,