Improve TUI timestamp consistency and formatting

src/frontends/tui/components/App.tsx

@@ -78,10 +78,19 @@ export function App({
   onTransfer,
   onExit,
 }: AppProps): React.ReactElement {
+  const ensureTimestamp = useCallback((message: Message): Message => ({
+    ...message,
+    timestamp: message.timestamp ?? Date.now(),
+  }), []);
+
+  const ensureTimestamps = useCallback((history: Message[]): Message[] => (
+    history.map(ensureTimestamp)
+  ), [ensureTimestamp]);
+
   const ctrlCExitWindowMs = 1_500;
   const { exit } = useApp();
   const [input, setInput] = useState('');
-  const [messages, setMessages] = useState<Message[]>(session.getHistory());
+  const [messages, setMessages] = useState<Message[]>(ensureTimestamps(session.getHistory()));
   const [isStreaming, setIsStreaming] = useState(false);
   const [streamingContent, setStreamingContent] = useState('');
   const [scrollOffset, setScrollOffset] = useState(0);
@@ -682,7 +691,7 @@ export function App({
       const messageWithTimestamp = session.addMessage(userMessage);
       setMessages(prev => [...prev, messageWithTimestamp]);
     } else {
-      setMessages(prev => [...prev, { ...userMessage, timestamp: Date.now() }]);
+      setMessages(prev => [...prev, ensureTimestamp(userMessage)]);
     }
     setScrollOffset(0);
 
@@ -696,7 +705,7 @@ export function App({
         await agent.process(command.content);
         const usage = agent.getUsage();
         setTokenUsage({ inputTokens: usage.inputTokens, outputTokens: usage.outputTokens });
-        setMessages(session.getHistory());
+        setMessages(ensureTimestamps(session.getHistory()));
       } else if (modelClient.chatStream) {
         let fullContent = '';
 
@@ -757,6 +766,8 @@ export function App({
     exit,
     onExit,
     isStreaming,
+    ensureTimestamp,
+    ensureTimestamps,
     messages.length,
     tokenUsage.inputTokens,
     tokenUsage.outputTokens,