fix: preserve real cancellation in MCP paths

nanobot/agent/loop.py

@@ -81,6 +81,7 @@ from nanobot.session.manager import (
     replay_max_messages_for_context,
 )
 from nanobot.triggers.local_turns import LocalTriggerTurnCoordinator
+from nanobot.utils.cancellation import task_is_cancelling
 from nanobot.utils.document import extract_documents, reference_non_image_attachments
 from nanobot.utils.helpers import image_placeholder_text
 from nanobot.utils.helpers import truncate_text as truncate_text_fn
@@ -998,8 +999,11 @@ class AgentLoop:
                 except asyncio.CancelledError:
                     # Preserve real task cancellation so shutdown can complete cleanly.
                     # Only ignore non-task CancelledError signals that may leak from integrations.
-                    if not self._running or asyncio.current_task().cancelling():
+                    if not self._running or task_is_cancelling():
                         raise
+                    logger.warning(
+                        "Ignoring leaked CancelledError while consuming inbound messages"
+                    )
                     continue
                 except Exception as e:
                     logger.warning("Error consuming inbound message: {}, continuing...", e)

nanobot/agent/tools/mcp.py

@@ -30,6 +30,7 @@ from nanobot.security.network import (
     resolve_url_target,
     validate_url_target,
 )
+from nanobot.utils.cancellation import task_is_cancelling
 
 # Transient connection errors that warrant a single retry.
 # These typically happen when an MCP server restarts or a network
@@ -487,8 +488,7 @@ class MCPToolWrapper(_MCPWrapperBase):
             except asyncio.CancelledError:
                 # MCP SDK's anyio cancel scopes can leak CancelledError on timeout/failure.
                 # Re-raise only if our task was externally cancelled (e.g. /stop).
-                task = asyncio.current_task()
-                if task is not None and task.cancelling() > 0:
+                if task_is_cancelling():
                     raise
                 logger.warning("MCP tool '{}' was cancelled by server/SDK", self._name)
                 return ToolResult.error("(MCP tool call was cancelled)")
@@ -650,8 +650,7 @@ class MCPResourceWrapper(_MCPWrapperBase):
                 )
                 return f"(MCP resource read timed out after {self._resource_timeout}s)"
             except asyncio.CancelledError:
-                task = asyncio.current_task()
-                if task is not None and task.cancelling() > 0:
+                if task_is_cancelling():
                     raise
                 logger.warning("MCP resource '{}' was cancelled by server/SDK", self._name)
                 return "(MCP resource read was cancelled)"
@@ -764,8 +763,7 @@ class MCPPromptWrapper(_MCPWrapperBase):
                 )
                 return f"(MCP prompt call timed out after {self._prompt_timeout}s)"
             except asyncio.CancelledError:
-                task = asyncio.current_task()
-                if task is not None and task.cancelling() > 0:
+                if task_is_cancelling():
                     raise
                 logger.warning("MCP prompt '{}' was cancelled by server/SDK", self._name)
                 return "(MCP prompt call was cancelled)"
@@ -1145,6 +1143,8 @@ async def connect_missing_servers(state: Any, registry: ToolRegistry) -> None:
             else:
                 logger.warning("No MCP servers connected successfully (will retry next message)")
         except asyncio.CancelledError:
+            if task_is_cancelling():
+                raise
             logger.warning("MCP connection cancelled (will retry next message)")
         except BaseException as e:
             logger.warning("Failed to connect MCP servers (will retry next message): {}", e)
@@ -1411,7 +1411,7 @@ async def _close_server(state: Any, server_name: str) -> None:
     try:
         await stack.aclose()
     except asyncio.CancelledError:
-        if asyncio.current_task().cancelling() > 0:
+        if task_is_cancelling():
             raise
         logger.debug("MCP server '{}' cleanup error (can be ignored)", server_name)
     except (RuntimeError, BaseExceptionGroup):
@@ -1428,7 +1428,7 @@ async def close_mcp_servers(state: Any) -> None:
             try:
                 await connection.aclose()
             except asyncio.CancelledError:
-                if asyncio.current_task().cancelling() > 0:
+                if task_is_cancelling():
                     raise
                 logger.debug("MCP server '{}' cleanup error (can be ignored)", name)
             except (RuntimeError, BaseExceptionGroup):

nanobot/utils/cancellation.py

@@ -0,0 +1,10 @@
+"""Async cancellation helpers."""
+
+from __future__ import annotations
+
+import asyncio
+
+
+def task_is_cancelling() -> bool:
+    task = asyncio.current_task()
+    return task is not None and task.cancelling() > 0

tests/agent/test_task_cancel.py

@@ -111,6 +111,34 @@ class TestHandleStop:
 
 
 class TestDispatch:
+    @pytest.mark.asyncio
+    async def test_run_logs_and_continues_after_leaked_cancelled_error(self, monkeypatch):
+        loop, bus = _make_loop()
+        loop._connect_mcp = AsyncMock()
+        loop.close_mcp = AsyncMock()
+        loop.auto_compact.check_expired = MagicMock()
+        warnings: list[str] = []
+        calls = 0
+
+        async def consume_once_then_stop():
+            nonlocal calls
+            calls += 1
+            if calls == 1:
+                raise asyncio.CancelledError()
+            loop.stop()
+            raise asyncio.TimeoutError()
+
+        monkeypatch.setattr(bus, "consume_inbound", consume_once_then_stop)
+        monkeypatch.setattr(
+            "nanobot.agent.loop.logger.warning",
+            lambda message, *args, **kwargs: warnings.append(message),
+        )
+
+        await loop.run()
+
+        assert calls == 2
+        assert any("Ignoring leaked CancelledError" in warning for warning in warnings)
+
     def test_exec_tool_not_registered_when_disabled(self):
         from nanobot.agent.tools.shell import ExecToolConfig
         from nanobot.config.schema import ToolsConfig

tests/tools/test_mcp_tool.py

@@ -144,6 +144,35 @@ def _make_wrapper(session: object, *, timeout: float = 0.1) -> MCPToolWrapper:
     return MCPToolWrapper(session, "test", tool_def, tool_timeout=timeout)
 
 
+@pytest.mark.asyncio
+async def test_connect_missing_servers_propagates_external_cancellation(monkeypatch) -> None:
+    started = asyncio.Event()
+
+    async def connect_mcp_servers(_servers: dict, _registry: ToolRegistry) -> dict:
+        started.set()
+        await asyncio.sleep(60)
+        return {}
+
+    class State:
+        pass
+
+    state = State()
+    state._mcp_closing = False
+    state._mcp_servers = {"test": MCPServerConfig(command="fake")}
+    state._mcp_stacks = {}
+    state._mcp_connecting = False
+    monkeypatch.setattr(mcp_mod, "connect_mcp_servers", connect_mcp_servers)
+
+    task = asyncio.create_task(mcp_mod.connect_missing_servers(state, ToolRegistry()))
+    await asyncio.wait_for(started.wait(), timeout=1.0)
+    task.cancel()
+
+    with pytest.raises(asyncio.CancelledError):
+        await task
+
+    assert state._mcp_connecting is False
+
+
 def test_wrapper_preserves_non_nullable_unions() -> None:
     tool_def = SimpleNamespace(
         name="demo",