From 24805200f0c8ba8db4a3d3317b2835f7739cf9a7 Mon Sep 17 00:00:00 2001
From: siwuai <458372151@qq.com>
Date: Wed, 8 Apr 2026 10:03:07 +0800
Subject: [PATCH] fix(frontend): prevent stale 'new' thread ID from triggering
 422 history requests (#1960)

After history.replaceState updates the URL from /chats/new to
/chats/{UUID}, Next.js useParams does not update because replaceState
bypasses the router. The useEffect in useThreadChat would then set
threadIdFromPath ('new') as the threadId, causing the LangGraph SDK
to call POST /threads/new/history which returns HTTP 422 (Invalid
thread ID: must be a UUID).

This fix adds a guard to skip the threadId update when
threadIdFromPath is the literal string 'new', preserving the
already-correct UUID that was set when the thread was created.
---
 .../src/components/workspace/chats/use-thread-chat.ts     | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/frontend/src/components/workspace/chats/use-thread-chat.ts b/frontend/src/components/workspace/chats/use-thread-chat.ts
index 85e7db1a8..6913e3b76 100644
--- a/frontend/src/components/workspace/chats/use-thread-chat.ts
+++ b/frontend/src/components/workspace/chats/use-thread-chat.ts
@@ -24,6 +24,14 @@ export function useThreadChat() {
       setThreadId(uuid());
       return;
     }
+    // Guard: after history.replaceState updates the URL from /chats/new to
+    // /chats/{UUID}, Next.js useParams may still return the stale "new" value
+    // because replaceState does not trigger router updates.  Avoid propagating
+    // this invalid thread ID to downstream hooks (e.g. useStream), which would
+    // cause a 422 from LangGraph Server.
+    if (threadIdFromPath === "new") {
+      return;
+    }
     setIsNewThread(false);
     setThreadId(threadIdFromPath);
   }, [pathname, threadIdFromPath]);