fix(chat): update navigation method to prevent state loss during thread remount (#1107)

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

@@ -43,6 +43,7 @@ export default function AgentChatPage() {
     context: { ...settings.context, agent_name: agent_name },
     onStart: () => {
       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,
         "",

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

@@ -1,8 +1,5 @@
 "use client";
 
-import { useParams } from "next/navigation";
-import { useEffect, useRef, useState } from "react";
-
 import { PromptInputProvider } from "@/components/ai-elements/prompt-input";
 import { ArtifactsProvider } from "@/components/workspace/artifacts";
 import { SubtasksProvider } from "@/core/tasks/context";
@@ -12,24 +9,8 @@ export default function ChatLayout({
 }: {
   children: React.ReactNode;
 }) {
-  const { thread_id } = useParams<{ thread_id: string }>();
-  const prevThreadId = useRef(thread_id);
-
-  // Increment only when navigating TO "new" from a non-"new" route.
-  // This forces a full remount of the subtree for a fresh new-chat state,
-  // without remounting when the URL transitions from "new" → actual-id
-  // (which would interrupt streaming).
-  const [generation, setGeneration] = useState(0);
-
-  useEffect(() => {
-    if (thread_id === "new" && prevThreadId.current !== "new") {
-      setGeneration((g) => g + 1);
-    }
-    prevThreadId.current = thread_id;
-  }, [thread_id]);
-
   return (
-    <SubtasksProvider key={generation}>
+    <SubtasksProvider>
       <ArtifactsProvider>
         <PromptInputProvider>{children}</PromptInputProvider>
       </ArtifactsProvider>

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

@@ -1,6 +1,5 @@
 "use client";
 
-import { useRouter } from "next/navigation";
 import { useCallback } from "react";
 
 import { type PromptInputMessage } from "@/components/ai-elements/prompt-input";
@@ -26,7 +25,6 @@ import { cn } from "@/lib/utils";
 
 export default function ChatPage() {
   const { t } = useI18n();
-  const router = useRouter();
   const [settings, setSettings] = useLocalSettings();
 
   const { threadId, isNewThread, setIsNewThread, isMock } = useThreadChat();
@@ -40,11 +38,8 @@ export default function ChatPage() {
     isMock,
     onStart: () => {
       setIsNewThread(false);
-      // Use router.replace so Next.js Router's internal state is updated.
-      // This ensures subsequent "New Chat" clicks are treated as a real
-      // cross-route navigation (actual-id → "new") rather than a no-op
-      // same-path navigation, which was causing stale content to persist.
-      router.replace(`/workspace/chats/${threadId}`);
+      // ! Important: Never use next.js router for navigation in this case, otherwise it will cause the thread to re-mount and lose all states. Use native history API instead.
+      history.replaceState(null, "", `/workspace/chats/${threadId}`);
     },
     onFinish: (state) => {
       if (document.hidden || !document.hasFocus()) {