chore: import upstream snapshot with attribution

apps/sim/blocks/custom/overlay.test.ts

@@ -0,0 +1,41 @@
+/**
+ * @vitest-environment node
+ */
+import { afterEach, describe, expect, it } from 'vitest'
+import { buildCustomBlockConfig } from '@/blocks/custom/build-config'
+import {
+  overlayBlocks,
+  registerBlockOverlayResolver,
+  resolveOverlayBlock,
+} from '@/blocks/custom/overlay'
+import type { BlockIcon } from '@/blocks/types'
+
+const icon: BlockIcon = () => null as never
+
+const config = buildCustomBlockConfig(
+  { type: 'custom_block_xyz', name: 'X', description: '', workflowId: 'wf-9' },
+  [],
+  { icon }
+)
+
+afterEach(() => registerBlockOverlayResolver(null))
+
+describe('block overlay resolver', () => {
+  it('returns undefined/empty with no resolver registered', () => {
+    expect(resolveOverlayBlock('custom_block_xyz')).toBeUndefined()
+    expect(overlayBlocks()).toEqual([])
+  })
+
+  it('resolves through a registered resolver and clears on null', () => {
+    const map = new Map([[config.type, config]])
+    registerBlockOverlayResolver({ get: (t) => map.get(t), all: () => [...map.values()] })
+
+    expect(resolveOverlayBlock('custom_block_xyz')).toBe(config)
+    expect(resolveOverlayBlock('nope')).toBeUndefined()
+    expect(overlayBlocks()).toEqual([config])
+
+    registerBlockOverlayResolver(null)
+    expect(resolveOverlayBlock('custom_block_xyz')).toBeUndefined()
+    expect(overlayBlocks()).toEqual([])
+  })
+})