fix(frontend): isolate new chat thread messages (#3508)

* fix(frontend): isolate new chat thread messages

* fix(frontend): keep live messages visible in new chat

* fix(frontend): reset thread-local message refs

frontend/src/app/workspace/agents/[agent_name]/chats/[thread_id]/page.tsx

@@ -72,20 +72,21 @@ export default function AgentChatPage() {
     loadMoreHistory,
   } = useThreadStream({
     threadId: isNewThread ? undefined : threadId,
+    displayThreadId: threadId,
     context: { ...settings.context, agent_name: agent_name },
     isMock,
     onSend: () => {
       setIsWelcomeMode(false);
     },
     onStart: (createdThreadId) => {
-      setThreadId(createdThreadId);
-      setIsNewThread(false);
       // ! Important: Never use next.js router for navigation in this case, otherwise it will cause the thread to re-mount and lose all states. Use native history API instead.
       history.replaceState(
         null,
         "",
         `/workspace/agents/${agent_name}/chats/${createdThreadId}`,
       );
+      setThreadId(createdThreadId);
+      setIsNewThread(false);
     },
     onFinish: (state) => {
       if (document.hidden || !document.hasFocus()) {

frontend/src/app/workspace/chats/[thread_id]/page.tsx

@@ -75,6 +75,7 @@ export default function ChatPage() {
     loadMoreHistory,
   } = useThreadStream({
     threadId: isNewThread ? undefined : threadId,
+    displayThreadId: threadId,
     context: settings.context,
     isMock,
     // onSend only animates the UI; do NOT flip `isNewThread` here — the
@@ -84,10 +85,10 @@ export default function ChatPage() {
       setIsWelcomeMode(false);
     },
     onStart: (createdThreadId) => {
-      setThreadId(createdThreadId);
-      setIsNewThread(false);
       // ! Important: Never use next.js router for navigation in this case, otherwise it will cause the thread to re-mount and lose all states. Use native history API instead.
       history.replaceState(null, "", `/workspace/chats/${createdThreadId}`);
+      setThreadId(createdThreadId);
+      setIsNewThread(false);
     },
     onFinish: (state) => {
       if (document.hidden || !document.hasFocus()) {