Fix session cancel and new task routing

backend/api/server.py

@@ -927,6 +927,28 @@ class AgentState:
                 self._run_locks[key] = lock
             return lock
 
+    def abandon_session_runtime(
+        self,
+        account_id: str | None = None,
+        session_id: str | None = None,
+    ) -> bool:
+        """Stop routing future requests through the currently held runtime.
+
+        A user cancel can happen while the worker thread is blocked inside a
+        model HTTP request or a remote runtime call. Python cannot safely
+        release a Lock owned by another thread, so the correct cancellation
+        behavior is to abandon that lock object for future turns.
+
+        The agent instance is abandoned together with the lock. The old worker
+        may still mutate its LocalCodingAgent.tool_context during unwind; a new
+        user turn must not share that object.
+        """
+        key = self._session_key(account_id, session_id)
+        with self._lock:
+            removed_lock = self._run_locks.pop(key, None) is not None
+            removed_agent = self._agents.pop(key, None) is not None
+            return removed_lock or removed_agent
+
     def update(
         self,
         *,
@@ -2322,6 +2344,7 @@ def create_app(state: AgentState) -> FastAPI:
         if payload.run_id and state.run_manager.cancel_run(payload.run_id):
             cancelled_ids.add(payload.run_id)
         cancelled_ids.update(state.run_manager.cancel_session(account_key, safe_id))
+        abandoned_runtime = state.abandon_session_runtime(account_key, safe_id)
         cancelled_bg_task_ids = await _bash_bg_manager.cancel_session(
             state,
             account_key,
@@ -2334,7 +2357,7 @@ def create_app(state: AgentState) -> FastAPI:
             stage='用户已取消',
         )
         cancelled_ids.update(stored_cancelled)
-        cancelled = bool(cancelled_ids or cancelled_bg_task_ids)
+        cancelled = bool(cancelled_ids or cancelled_bg_task_ids or abandoned_runtime)
         if cancelled:
             _mark_session_interrupted(
                 state.account_paths(payload.account_id)['sessions'],
@@ -2346,6 +2369,7 @@ def create_app(state: AgentState) -> FastAPI:
             'cancelled': cancelled,
             'cancelled_run_ids': sorted(cancelled_ids),
             'cancelled_bg_task_ids': sorted(cancelled_bg_task_ids),
+            'abandoned_runtime': abandoned_runtime,
         }
 
     def _run_chat_payload(