fix(gateway): make resource teardown cancellation-safe

tests/agent/test_task_cancel.py

@@ -55,6 +55,62 @@ class TestHandleStop:
         out = await cmd_stop(ctx)
         assert "No active task" in out.content
 
+    @pytest.mark.asyncio
+    async def test_close_mcp_cancels_active_turn_before_resources(self):
+        loop, _bus = _make_loop()
+        events: list[str] = []
+
+        async def active_turn():
+            try:
+                await asyncio.sleep(60)
+            except asyncio.CancelledError:
+                events.append("turn_cancelled")
+                raise
+
+        task = asyncio.create_task(active_turn())
+        await asyncio.sleep(0)
+        loop._active_tasks["test:c1"] = {task}
+
+        async def close_subagents():
+            events.append("resources_closed")
+
+        loop.subagents.close = close_subagents
+        loop._exec_session_manager.close_all = AsyncMock()
+        with patch("nanobot.agent.loop.agent_context.close_mcp", AsyncMock()):
+            await loop.close_mcp()
+
+        assert events == ["turn_cancelled", "resources_closed"]
+        assert task.cancelled()
+
+    @pytest.mark.asyncio
+    async def test_close_mcp_serializes_duplicate_cleanup(self):
+        loop, _bus = _make_loop()
+        entered = asyncio.Event()
+        release = asyncio.Event()
+        concurrent = 0
+        max_concurrent = 0
+
+        async def close_subagents():
+            nonlocal concurrent, max_concurrent
+            concurrent += 1
+            max_concurrent = max(max_concurrent, concurrent)
+            entered.set()
+            await release.wait()
+            concurrent -= 1
+
+        loop.subagents.close = close_subagents
+        loop._exec_session_manager.close_all = AsyncMock()
+        with patch("nanobot.agent.loop.agent_context.close_mcp", AsyncMock()):
+            first = asyncio.create_task(loop.close_mcp())
+            await entered.wait()
+            second = asyncio.create_task(loop.close_mcp())
+            await asyncio.sleep(0)
+            assert not second.done()
+            release.set()
+            await asyncio.gather(first, second)
+
+        assert max_concurrent == 1
+
     @pytest.mark.asyncio
     async def test_stop_cancels_active_task(self):
         from nanobot.bus.events import InboundMessage