fix: scope Socket.IO event-caller to the requesting user's own session (#25763)

get_event_call() routed execute:python / execute:tool events to a client-supplied session_id after only checking the session was connected, not that it belonged to the requester. Verify the target session is owned by the requesting user (metadata user_id) before delivering, so a client cannot route code/tool execution into another user's session.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/open_webui/socket/main.py

@@ -1022,9 +1022,10 @@ async def get_event_call(request_info):
     async def __event_caller__(event_data):
         session_id = request_info['session_id']
 
-        # Fast-fail if the client has disconnected.
-        if session_id not in SESSION_POOL:
-            log.warning(f'Event caller: session {session_id} no longer connected')
+        # session_id is client-supplied; only the requesting user's own live session may be targeted.
+        session = SESSION_POOL.get(session_id)
+        if session is None or session.get('id') != request_info.get('user_id'):
+            log.warning(f'Event caller: session {session_id} not owned by requesting user or disconnected')
             return {'error': 'Client session disconnected.'}
 
         try: