Persist AI Chat session to localStorage

Messages survive page navigation and browser refresh. The session is
loaded from localStorage on mount and saved on every change. The clear
button removes the stored session. Timestamps are serialized as ISO
strings and NostrEvent objects serialize as plain JSON.

src/pages/AIChatPage.tsx

@@ -413,6 +413,35 @@ Keep spell names short and descriptive (2-4 words). When you create a spell, bri
 Be concise and friendly. When you use a tool, briefly describe what you created.`,
 };
 
+// ─── Chat Persistence ───
+
+const CHAT_STORAGE_KEY = 'ditto:ai-chat-messages';
+
+/** Serialized shape stored in localStorage (Date → ISO string). */
+interface StoredMessage extends Omit<DisplayMessage, 'timestamp'> {
+  timestamp: string;
+}
+
+function loadMessages(): DisplayMessage[] {
+  try {
+    const raw = localStorage.getItem(CHAT_STORAGE_KEY);
+    if (!raw) return [];
+    const stored: StoredMessage[] = JSON.parse(raw);
+    return stored.map((m) => ({ ...m, timestamp: new Date(m.timestamp) }));
+  } catch {
+    return [];
+  }
+}
+
+function saveMessages(messages: DisplayMessage[]): void {
+  try {
+    const stored: StoredMessage[] = messages.map((m) => ({ ...m, timestamp: m.timestamp.toISOString() }));
+    localStorage.setItem(CHAT_STORAGE_KEY, JSON.stringify(stored));
+  } catch {
+    // Storage full or unavailable — silently ignore
+  }
+}
+
 // ─── Page Component ───
 
 export function AIChatPage() {
@@ -421,7 +450,7 @@ export function AIChatPage() {
   const { sendChatMessage, getAvailableModels, isLoading: apiLoading, error: apiError, clearError } = useShakespeare();
   const { executeToolCall } = useToolExecutor();
 
-  const [messages, setMessages] = useState<DisplayMessage[]>([]);
+  const [messages, setMessages] = useState<DisplayMessage[]>(loadMessages);
   const [input, setInput] = useState('');
   const [isStreaming, setIsStreaming] = useState(false);
   const [models, setModels] = useState<Model[]>([]);
@@ -439,6 +468,11 @@ export function AIChatPage() {
 
   useLayoutOptions({ noOverscroll: true });
 
+  // Persist messages to localStorage
+  useEffect(() => {
+    saveMessages(messages);
+  }, [messages]);
+
   // Scroll to bottom on new messages
   const scrollToBottom = useCallback(() => {
     messagesEndRef.current?.scrollIntoView({ behavior: 'smooth' });
@@ -619,6 +653,7 @@ export function AIChatPage() {
   // Clear conversation
   const handleClear = useCallback(() => {
     setMessages([]);
+    localStorage.removeItem(CHAT_STORAGE_KEY);
     clearError();
   }, [clearError]);