chore: import upstream snapshot with attribution

apps/sim/blocks/custom/client-overlay.ts

@@ -0,0 +1,61 @@
+'use client'
+
+import { useSyncExternalStore } from 'react'
+import { registerBlockOverlayResolver } from '@/blocks/custom/overlay'
+import type { BlockConfig } from '@/blocks/types'
+
+/**
+ * Client-side custom-block overlay: a mutable Map, hydrated from
+ * `useCustomBlocks` by `CustomBlocksProvider`, that the `@/blocks/registry`
+ * accessors fall back to. Scoped to the active workspace's org; re-hydrated on
+ * workspace switch.
+ *
+ * Because many consumers snapshot `getAllBlocks()` (the cmd+K search, the Access
+ * Control block list), the overlay is also an external store: `version` bumps on
+ * every hydrate and listeners are notified, so those consumers can re-read via
+ * {@link useCustomBlockOverlayVersion} instead of going stale until a refresh.
+ */
+let map = new Map<string, BlockConfig>()
+let version = 0
+const listeners = new Set<() => void>()
+
+registerBlockOverlayResolver({
+  get: (type) => map.get(type),
+  all: () => [...map.values()],
+})
+
+/**
+ * Bump the overlay version and notify subscribers that block-registry-derived
+ * data changed. Shared signal for BOTH custom-block hydration and the
+ * block-visibility hydrate path — subscribers treat the version as an opaque
+ * "re-read `getAllBlocks()`" token, never as "custom blocks specifically
+ * changed".
+ */
+export function notifyBlockOverlayChanged(): void {
+  version += 1
+  for (const listener of listeners) listener()
+}
+
+/** Replace the in-scope custom blocks and notify subscribers. */
+export function hydrateClientCustomBlocks(configs: BlockConfig[]): void {
+  map = new Map(configs.map((config) => [config.type, config]))
+  notifyBlockOverlayChanged()
+}
+
+function subscribe(listener: () => void): () => void {
+  listeners.add(listener)
+  return () => listeners.delete(listener)
+}
+
+/**
+ * Subscribe a component to overlay changes. Returns a monotonic version that
+ * changes on every hydrate — include it in a `useMemo`/`useEffect` dep list to
+ * recompute anything derived from `getAllBlocks()` when custom blocks load.
+ */
+export function useCustomBlockOverlayVersion(): number {
+  return useSyncExternalStore(
+    subscribe,
+    () => version,
+    () => 0
+  )
+}