fix: deep-freeze DEFAULT_STATE nested arrays to prevent shared mutation

Amp-Thread-ID: https://ampcode.com/threads/T-019cbd94-a928-7610-b468-2583f4816262

src/stores/nodeImageStore.test.ts

@@ -305,6 +305,25 @@ describe(useNodeImageStore, () => {
     })
   })
 
+  describe('DEFAULT_STATE immutability', () => {
+    it('default imageRects is frozen and cannot be mutated', () => {
+      const node = createMockNode()
+      mockNodeToNodeLocatorId.mockReturnValue(locatorA)
+
+      store.installPropertyProjection(node)
+
+      // Read default imageRects without triggering state creation
+      const nodeB = createMockNode()
+      mockNodeToNodeLocatorId.mockReturnValue(locatorB)
+      store.installPropertyProjection(nodeB)
+
+      // Default arrays should be frozen (no state entry exists yet)
+      expect(() => {
+        ;(nodeB.imageRects as unknown[]).push([0, 0, 10, 10])
+      }).toThrow()
+    })
+  })
+
   describe('null-to-null transitions', () => {
     it('imageIndex null → null works', () => {
       const node = createMockNode()

src/stores/nodeImageStore.ts

@@ -17,8 +17,6 @@ interface NodeImageState {
   overIndex: number | null
 }
 
-const DEFAULT_STATE = Object.freeze(createDefaultState())
-
 function createDefaultState(): NodeImageState {
   return {
     imgs: [],
@@ -29,6 +27,12 @@ function createDefaultState(): NodeImageState {
   }
 }
 
+const DEFAULT_STATE: Readonly<NodeImageState> = Object.freeze({
+  ...createDefaultState(),
+  imgs: Object.freeze([]) as unknown as HTMLImageElement[],
+  imageRects: Object.freeze([]) as unknown as Rect[]
+})
+
 /**
  * Module-scoped resolver for converting nodes to locator IDs.
  * Set once during app bootstrap via {@link setNodeLocatorResolver} to