fix: sync useLocalStorage across same-tab consumers of one key

Per review: the Notes app is explicitly non-singleton, so opening two
"New Note" windows meant two DraftNote instances writing the same
localStorage key independently — the native `storage` event only
fires in *other* tabs/documents, never the one that wrote, so the two
windows would silently diverge (discard/publish in one wouldn't
update the other).

useLocalStorage now also dispatches a same-document custom event on
every write, and every instance sharing that key listens for it —
verified live with two open draft windows staying in sync as one is
typed into.

Also dropped a redundant `{}` params argument on an openApp() call
that every other call site omits when opening with no parameters.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BYiUtZMQeA5RHggQw73wto

src/apps/feed/index.tsx

@@ -91,7 +91,7 @@ export default function FeedApp({ setTitle }: AppProps) {
             variant="ghost"
             size="sm"
             className="h-7 gap-1.5 px-2 text-xs"
-            onClick={() => openApp('notes', {})}
+            onClick={() => openApp('notes')}
           >
             <FileText className="size-3.5" aria-hidden />
             New note

src/hooks/useLocalStorage.ts

@@ -1,4 +1,19 @@
-import { useState, useEffect } from 'react';
+import { useCallback, useEffect, useState } from 'react';
+
+/**
+ * Fired on `window` whenever `useLocalStorage` writes a key, so every
+ * component sharing that key *within this document* stays in sync — the
+ * native `storage` event only fires in *other* tabs/documents, never the
+ * one that made the write. Without this, e.g. two "New Note" draft windows
+ * open at once would silently diverge: each holds its own React state, both
+ * write to the same localStorage entry, and neither sees the other's edits.
+ */
+const LOCAL_STORAGE_EVENT = 'app:local-storage';
+
+interface LocalStorageEventDetail {
+  key: string;
+  value: string;
+}
 
 /**
  * Generic hook for managing localStorage state
@@ -24,17 +39,30 @@ export function useLocalStorage<T>(
     }
   });
 
-  const setValue = (value: T | ((prev: T) => T)) => {
-    try {
-      const valueToStore = value instanceof Function ? value(state) : value;
-      setState(valueToStore);
-      localStorage.setItem(key, serialize(valueToStore));
-    } catch (error) {
-      console.warn(`Failed to save ${key} to localStorage:`, error);
-    }
-  };
+  const setValue = useCallback(
+    (value: T | ((prev: T) => T)) => {
+      setState((prev) => {
+        try {
+          const valueToStore = value instanceof Function ? value(prev) : value;
+          const serialized = serialize(valueToStore);
+          localStorage.setItem(key, serialized);
+          window.dispatchEvent(
+            new CustomEvent<LocalStorageEventDetail>(LOCAL_STORAGE_EVENT, {
+              detail: { key, value: serialized },
+            }),
+          );
+          return valueToStore;
+        } catch (error) {
+          console.warn(`Failed to save ${key} to localStorage:`, error);
+          return prev;
+        }
+      });
+    },
+    [key, serialize],
+  );
 
-  // Sync with localStorage changes from other tabs
+  // Sync with localStorage changes from other tabs, and from other
+  // components sharing this key in this tab (see LOCAL_STORAGE_EVENT above).
   useEffect(() => {
     const handleStorageChange = (e: StorageEvent) => {
       if (e.key === key && e.newValue !== null) {
@@ -45,10 +73,23 @@ export function useLocalStorage<T>(
         }
       }
     };
+    const handleLocalChange = (e: Event) => {
+      const detail = (e as CustomEvent<LocalStorageEventDetail>).detail;
+      if (detail?.key !== key) return;
+      try {
+        setState(deserialize(detail.value));
+      } catch (error) {
+        console.warn(`Failed to sync ${key} from localStorage:`, error);
+      }
+    };
 
     window.addEventListener('storage', handleStorageChange);
-    return () => window.removeEventListener('storage', handleStorageChange);
+    window.addEventListener(LOCAL_STORAGE_EVENT, handleLocalChange);
+    return () => {
+      window.removeEventListener('storage', handleStorageChange);
+      window.removeEventListener(LOCAL_STORAGE_EVENT, handleLocalChange);
+    };
   }, [key, deserialize]);
 
   return [state, setValue] as const;
-}
+}