Update app.py

app.py

@@ -57,7 +57,8 @@ import concurrent.futures
 # Define global variables for managing the thread and future
 executor = concurrent.futures.ThreadPoolExecutor(max_workers=1)
 future = None
-stop_event = concurrent.futures.thread.Event()
+import threading
+stop_event = threading.Event()
 
 # LangFuse API keys and host settings
 os.environ["LANGFUSE_PUBLIC_KEY"] = os.getenv("LANGFUSE_PUBLIC_KEY")