diff --git a/backend/api/server.py b/backend/api/server.py
index 7f40d26..96747e8 100644
--- a/backend/api/server.py
+++ b/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(
diff --git a/frontend/app/app/assistant.tsx b/frontend/app/app/assistant.tsx
index 2d11245..182190d 100644
--- a/frontend/app/app/assistant.tsx
+++ b/frontend/app/app/assistant.tsx
@@ -255,12 +255,15 @@ function AssistantWorkspace() {
 			setActiveSessionId(next);
 		};
 		const handleChanged = (event: Event) => {
-			const detail = (event as CustomEvent<{ sessionId?: string | null }>)
-				.detail;
-			const next =
-				detail?.sessionId ?? readSessionIdFromUrl() ?? readActiveSessionId();
+			const customEvent = event as CustomEvent<{ sessionId?: string | null }>;
+			const hasExplicitSession =
+				customEvent.detail &&
+				Object.prototype.hasOwnProperty.call(customEvent.detail, "sessionId");
+			const next = hasExplicitSession
+				? (customEvent.detail.sessionId ?? null)
+				: (readSessionIdFromUrl() ?? readActiveSessionId());
 			console.log("[active-session] event-changed", {
-				detailSessionId: detail?.sessionId,
+				detailSessionId: customEvent.detail?.sessionId,
 				next,
 			});
 			setActiveSessionId(next);
diff --git a/frontend/app/components/assistant-ui/thread-list.tsx b/frontend/app/components/assistant-ui/thread-list.tsx
index b3efc14..73e63ea 100644
--- a/frontend/app/components/assistant-ui/thread-list.tsx
+++ b/frontend/app/components/assistant-ui/thread-list.tsx
@@ -131,8 +131,8 @@ const ThreadListNew: FC = () => {
 			variant="outline"
 			className="aui-thread-list-new h-9 w-full justify-start gap-2 rounded-lg px-3 text-sm hover:bg-muted data-active:bg-muted"
 			onClick={() => {
-				clearActiveSessionId();
 				pushHomeUrl();
+				clearActiveSessionId();
 				clearSession();
 				window.dispatchEvent(new Event("claw-active-session-cleared"));
 			}}
diff --git a/frontend/app/components/assistant-ui/threadlist-sidebar.tsx b/frontend/app/components/assistant-ui/threadlist-sidebar.tsx
index 37016ce..91998b0 100644
--- a/frontend/app/components/assistant-ui/threadlist-sidebar.tsx
+++ b/frontend/app/components/assistant-ui/threadlist-sidebar.tsx
@@ -203,8 +203,8 @@ function CollapsedSidebarRail({
 				<CollapsedIconButton
 					label="新任务"
 					onClick={() => {
-						clearActiveSessionId();
 						pushHomeUrl();
+						clearActiveSessionId();
 						clearSession();
 						window.dispatchEvent(new Event("claw-active-session-cleared"));
 					}}
diff --git a/tests/test_gui_server.py b/tests/test_gui_server.py
index 11cc38c..91ede93 100644
--- a/tests/test_gui_server.py
+++ b/tests/test_gui_server.py
@@ -349,6 +349,29 @@ class GuiServerTests(unittest.TestCase):
             self.assertIsNotNone(row)
             self.assertEqual(row['status'], 'cancelled')
 
+    def test_cancel_run_abandons_held_session_lock(self) -> None:
+        with tempfile.TemporaryDirectory() as d:
+            client, state = _build_client(Path(d))
+            record = state.run_manager.start('alice', 'thread-1')
+            old_lock = state.run_lock_for('alice', 'thread-1')
+            self.assertTrue(old_lock.acquire(blocking=False))
+            old_agent = state.agent_for('alice', 'thread-1')
+            try:
+                response = client.post(
+                    '/api/runs/cancel',
+                    json={'account_id': 'alice', 'session_id': 'thread-1'},
+                )
+                self.assertEqual(response.status_code, 200)
+                self.assertTrue(response.json()['cancelled'])
+                self.assertTrue(record.cancel_event.is_set())
+                new_lock = state.run_lock_for('alice', 'thread-1')
+                self.assertIsNot(new_lock, old_lock)
+                self.assertTrue(new_lock.acquire(blocking=False))
+                new_lock.release()
+                self.assertIsNot(state.agent_for('alice', 'thread-1'), old_agent)
+            finally:
+                old_lock.release()
+
     def test_latest_run_prefers_running_over_queued_for_session(self) -> None:
         with tempfile.TemporaryDirectory() as d:
             client, state = _build_client(Path(d))