The error "Attempted to exit a cancel scope that isn't the current task's current cancel scope"

[doncat99]

Error

Traceback (most recent call last):
  File "/Users/huangdon/Documents/universe-platform/warehouse/plan_agent/main.py", line 77, in <module>
    asyncio.run(main())
  File "/Users/huangdon/miniconda3/envs/universe/lib/python3.11/asyncio/runners.py", line 190, in run
    return runner.run(main)
           ^^^^^^^^^^^^^^^^
  File "/Users/huangdon/miniconda3/envs/universe/lib/python3.11/asyncio/runners.py", line 118, in run
    return self._loop.run_until_complete(task)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/huangdon/miniconda3/envs/universe/lib/python3.11/asyncio/base_events.py", line 654, in run_until_complete
    return future.result()
           ^^^^^^^^^^^^^^^
  File "/Users/huangdon/Documents/universe-platform/warehouse/plan_agent/main.py", line 31, in main
    async with MCPConnectionManager(context.server_registry):
  File "/Users/huangdon/Documents/universe-platform/libs/mcp-agent/src/mcp_agent/mcp/mcp_connection_manager.py", line 186, in __aexit__
    await self._tg.__aexit__(exc_type, exc_val, exc_tb)
  File "/Users/huangdon/miniconda3/envs/universe/lib/python3.11/site-packages/anyio/_backends/_asyncio.py", line 778, in __aexit__
    return self.cancel_scope.__exit__(exc_type, exc_val, exc_tb)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/huangdon/miniconda3/envs/universe/lib/python3.11/site-packages/anyio/_backends/_asyncio.py", line 464, in __exit__
    raise RuntimeError(
RuntimeError: Attempted to exit a cancel scope that isn't the current tasks's current cancel scope

Why is This Happening?

This error typically occurs when an async task group (_tg) is being exited (aexit) from a different task than the one that created it.

In your traceback:

The error originates from MCPConnectionManager.aexit():

async with MCPConnectionManager(context.server_registry):

This means something is trying to exit the async with block improperly.
Inside MCPConnectionManager.aexit(), it calls:

await self._tg.__aexit__(exc_type, exc_val, exc_tb)

Here, self._tg is an AnyIO task group (possibly anyio.create_task_group()).
aexit() is called from a different task than the one that started the group.
AnyIO detects that the cancel_scope is being exited from the wrong task, leading to:

raise RuntimeError("Attempted to exit a cancel scope that isn't the current task's current cancel scope")

How to Fix It

There are a few possible causes and fixes:

✅ 1️⃣ Ensure the Task Group is Created & Exited in the Same Task
If MCPConnectionManager creates a task group like this:

async with anyio.create_task_group() as tg:
    self._tg = tg  # Storing task group

Then make sure _tg.aexit() is called within the same task that created it.

[saqadri]

@doncat99 can you please provide repro steps on when this error occurs for you? Would love to debug it