fix(threads): 避免隐式订阅 events 流

frontend/src/core/threads/hooks.ts

@@ -193,7 +193,10 @@ export function useThreadStream({
       handleStreamStart(meta.thread_id);
       setOnStreamThreadId(meta.thread_id);
     },
-    onLangChainEvent(event) {
+    onLangChainEvent:
+      onToolEnd == null
+        ? undefined
+        : (event) => {
             if (event.event === "on_tool_end") {
               listeners.current.onToolEnd?.({
                 name: event.name,