fix(dashboard): prevent stale DB data from overwriting newer localStorage layout

Two related fixes:
1. When localStorage has a saved layout, mark it as authoritative so a DB
   response carrying older data (e.g. from a save cancelled by navigating away
   within the 2-second debounce window) cannot overwrite it.
2. Flush any pending debounced DB save immediately on component unmount so
   that navigating away within the window doesn't silently lose changes.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/web/src/hooks/useDashboardLayout.ts

@@ -69,6 +69,8 @@ export function useDashboardLayout() {
   const hasHydratedFromStorageRef = useRef(false);
   // Holds the DB config that needs to be persisted to localStorage once userId is available.
   const pendingStorageSaveRef = useRef<ReturnType<typeof normalizeDashboardLayout> | null>(null);
+  // Holds the latest layout that has been queued for DB save but not yet flushed.
+  const pendingLayoutSaveRef = useRef<DashboardLayoutConfig | null>(null);
 
   // Once userId is known, hydrate from user-scoped localStorage (if no DB data yet).
   useEffect(() => {
@@ -79,6 +81,10 @@ export function useDashboardLayout() {
     hasHydratedFromStorageRef.current = true;
     if (stored) {
       setConfig(stored);
+      // Treat localStorage data as authoritative local state so a stale DB
+      // response (e.g. from a save that was cancelled by page navigation within
+      // the 2-second debounce window) cannot overwrite it.
+      hasLocalChangesBeforeHydrationRef.current = true;
     }
     // localStorage check is complete — show whatever we have now.
     setIsHydrated(true);
@@ -146,10 +152,21 @@ export function useDashboardLayout() {
     pendingStorageSaveRef.current = null;
   }, [userId]);
 
+  // Keep a ref to saveMutation so the unmount cleanup can call it without
+  // capturing a stale closure.
+  const saveMutationRef = useRef(saveMutation);
+  saveMutationRef.current = saveMutation;
+
+  // Flush any pending debounced DB save when the component unmounts so that
+  // navigating away within the 2-second window doesn't silently lose changes.
   useEffect(() => () => {
     if (saveTimeoutRef.current) {
       clearTimeout(saveTimeoutRef.current);
       saveTimeoutRef.current = null;
+      if (pendingLayoutSaveRef.current) {
+        saveMutationRef.current.mutate({ layout: pendingLayoutSaveRef.current });
+        pendingLayoutSaveRef.current = null;
+      }
     }
   }, []);
 
@@ -159,8 +176,10 @@ export function useDashboardLayout() {
     }
     const newConfig = normalizeDashboardLayout(nextConfig);
     if (userId) saveToStorage(userId, newConfig);
+    pendingLayoutSaveRef.current = newConfig;
     if (saveTimeoutRef.current) clearTimeout(saveTimeoutRef.current);
     saveTimeoutRef.current = setTimeout(() => {
+      pendingLayoutSaveRef.current = null;
       saveMutation.mutate({ layout: newConfig });
     }, 2000);
   }, [saveMutation, userId]);