diff --git a/frontend/src/hooks/useAutoSaveProject.ts b/frontend/src/hooks/useAutoSaveProject.ts
index 9692bf19..8f2b74a3 100644
--- a/frontend/src/hooks/useAutoSaveProject.ts
+++ b/frontend/src/hooks/useAutoSaveProject.ts
@@ -30,18 +30,36 @@ const IDLE: AutoSaveState = { status: 'idle', lastSavedAt: null, errorMessage: n
 
 let installedImpl: AutoSaveImpl | null = null;
 
+/** Hooks that mounted before an impl was installed, waiting to start it. */
+const installWaiters = new Set<() => void>();
+
 export function installAutoSaveImpl(impl: AutoSaveImpl | null): void {
   installedImpl = impl;
+  // Overlays load through a dynamic import that races the first React
+  // commit: a hook whose mount effect ran before the overlay chunk
+  // evaluated used to see `installedImpl === null` and stay idle for the
+  // whole life of the tab — no auto-save, no unload flush. Start those
+  // already-mounted hooks now that the impl exists.
+  if (impl) installWaiters.forEach((start) => start());
 }
 
 export function useAutoSaveProject(): AutoSaveState {
   const [state, setState] = useState<AutoSaveState>(IDLE);
 
   useEffect(() => {
-    if (!installedImpl) return;
-    return installedImpl(setState);
-    // Mount-only — impl is installed at module load, swapping at runtime is unsupported.
-    // eslint-disable-next-line react-hooks/exhaustive-deps
+    let cleanup: (() => void) | null = null;
+    const start = () => {
+      if (installedImpl && !cleanup) cleanup = installedImpl(setState);
+    };
+    start();
+    // Late-install support only — swapping a live impl at runtime is still
+    // unsupported (the first installed impl keeps running until unmount).
+    installWaiters.add(start);
+    return () => {
+      installWaiters.delete(start);
+      cleanup?.();
+      cleanup = null;
+    };
   }, []);
 
   return state;