Bug: missing MCP server causes a crash #469
Description
Issue
There are a lot of errors reported here - basically this happens when I try to run Cecli without my "browser" mcp running. Cecli runs fine when the server is running but this is the error when it is not.
If I comment out the MCP below, Cecli runs fine.
MCP in question:
"browser": {
"transport": "http",
"url": "http://localhost:8222/mcp"
}
Error:
unhandled exception during asyncio.run() shutdown
task: <Task finished name='mcp.shared.session.BaseSession._receive_loop' coro=<BaseSession._receive_loop() done, defined at /home/tom/.platformio/penv/lib/python3.14/site-packages/mcp/shared/session.py:351> exception=RuntimeError('dictionary changed size during iteration')>
Traceback (most recent call last):
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/streams/memory.py", line 117, in receive
return self.receive_nowait()
~~~~~~~~~~~~~~~~~~~^^
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/streams/memory.py", line 112, in receive_nowait
raise WouldBlock
anyio.WouldBlock
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/mcp/shared/session.py", line 357, in _receive_loop
async for message in self._read_stream:
...<76 lines>...
await self._handle_response(message)
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/abc/_streams.py", line 41, in __anext__
return await self.receive()
^^^^^^^^^^^^^^^^^^^^
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/streams/memory.py", line 125, in receive
await receive_event.wait()
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/_backends/_asyncio.py", line 1789, in wait
await self._event.wait()
File "/usr/lib/python3.14/asyncio/locks.py", line 213, in wait
await fut
asyncio.exceptions.CancelledError
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/mcp/shared/session.py", line 448, in _receive_loop
for id, stream in self._response_streams.items():
~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
RuntimeError: dictionary changed size during iteration
unhandled exception during asyncio.run() shutdown
task: <Task finished name='mcp.shared.session.BaseSession._receive_loop' coro=<BaseSession._receive_loop() done, defined at /home/tom/.platformio/penv/lib/python3.14/site-packages/mcp/shared/session.py:351> exception=RuntimeError('dictionary changed size during iteration')>
Traceback (most recent call last):
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/streams/memory.py", line 117, in receive
return self.receive_nowait()
~~~~~~~~~~~~~~~~~~~^^
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/streams/memory.py", line 112, in receive_nowait
raise WouldBlock
anyio.WouldBlock
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/mcp/shared/session.py", line 357, in _receive_loop
async for message in self._read_stream:
...<76 lines>...
await self._handle_response(message)
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/abc/_streams.py", line 41, in __anext__
return await self.receive()
^^^^^^^^^^^^^^^^^^^^
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/streams/memory.py", line 125, in receive
await receive_event.wait()
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/_backends/_asyncio.py", line 1789, in wait
await self._event.wait()
File "/usr/lib/python3.14/asyncio/locks.py", line 213, in wait
await fut
asyncio.exceptions.CancelledError
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/mcp/shared/session.py", line 448, in _receive_loop
for id, stream in self._response_streams.items():
~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
RuntimeError: dictionary changed size during iteration
unhandled exception during asyncio.run() shutdown
task: <Task finished name='mcp.shared.session.BaseSession._receive_loop' coro=<BaseSession._receive_loop() done, defined at /home/tom/.platformio/penv/lib/python3.14/site-packages/mcp/shared/session.py:351> exception=RuntimeError('dictionary changed size during iteration')>
Traceback (most recent call last):
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/streams/memory.py", line 117, in receive
return self.receive_nowait()
~~~~~~~~~~~~~~~~~~~^^
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/streams/memory.py", line 112, in receive_nowait
raise WouldBlock
anyio.WouldBlock
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/mcp/shared/session.py", line 357, in _receive_loop
async for message in self._read_stream:
...<76 lines>...
await self._handle_response(message)
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/abc/_streams.py", line 41, in __anext__
return await self.receive()
^^^^^^^^^^^^^^^^^^^^
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/streams/memory.py", line 125, in receive
await receive_event.wait()
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/_backends/_asyncio.py", line 1789, in wait
await self._event.wait()
File "/usr/lib/python3.14/asyncio/locks.py", line 213, in wait
await fut
asyncio.exceptions.CancelledError
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/mcp/shared/session.py", line 448, in _receive_loop
for id, stream in self._response_streams.items():
~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
RuntimeError: dictionary changed size during iteration
an error occurred during closing of asynchronous generator <async_generator object stdio_client at 0x7f7f39edbe10>
asyncgen: <async_generator object stdio_client at 0x7f7f39edbe10>
+ Exception Group Traceback (most recent call last):
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/_backends/_asyncio.py", line 783, in __aexit__
| raise BaseExceptionGroup(
| "unhandled errors in a TaskGroup", self._exceptions
| ) from None
| BaseExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
+-+---------------- 1 ----------------
| Traceback (most recent call last):
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/mcp/client/stdio/__init__.py", line 189, in stdio_client
| yield read_stream, write_stream
| GeneratorExit
+------------------------------------
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/mcp/client/stdio/__init__.py", line 183, in stdio_client
anyio.create_task_group() as tg,
~~~~~~~~~~~~~~~~~~~~~~~^^
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/_backends/_asyncio.py", line 789, in __aexit__
if self.cancel_scope.__exit__(type(exc), exc, exc.__traceback__):
~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/_backends/_asyncio.py", line 461, in __exit__
raise RuntimeError(
...<2 lines>...
)
RuntimeError: Attempted to exit cancel scope in a different task than it was entered in
an error occurred during closing of asynchronous generator <async_generator object stdio_client at 0x7f7f392b0320>
asyncgen: <async_generator object stdio_client at 0x7f7f392b0320>
+ Exception Group Traceback (most recent call last):
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/_backends/_asyncio.py", line 783, in __aexit__
| raise BaseExceptionGroup(
| "unhandled errors in a TaskGroup", self._exceptions
| ) from None
| BaseExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
+-+---------------- 1 ----------------
| Traceback (most recent call last):
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/mcp/client/stdio/__init__.py", line 189, in stdio_client
| yield read_stream, write_stream
| GeneratorExit
+------------------------------------
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/mcp/client/stdio/__init__.py", line 183, in stdio_client
anyio.create_task_group() as tg,
~~~~~~~~~~~~~~~~~~~~~~~^^
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/_backends/_asyncio.py", line 789, in __aexit__
if self.cancel_scope.__exit__(type(exc), exc, exc.__traceback__):
~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/_backends/_asyncio.py", line 461, in __exit__
raise RuntimeError(
...<2 lines>...
)
RuntimeError: Attempted to exit cancel scope in a different task than it was entered in
an error occurred during closing of asynchronous generator <async_generator object streamable_http_client at 0x7f7f392d8340>
asyncgen: <async_generator object streamable_http_client at 0x7f7f392d8340>
+ Exception Group Traceback (most recent call last):
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/_backends/_asyncio.py", line 783, in __aexit__
| raise BaseExceptionGroup(
| "unhandled errors in a TaskGroup", self._exceptions
| ) from None
| BaseExceptionGroup: unhandled errors in a TaskGroup (2 sub-exceptions)
+-+---------------- 1 ----------------
| Traceback (most recent call last):
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/httpx/_transports/default.py", line 101, in map_httpcore_exceptions
| yield
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/httpx/_transports/default.py", line 394, in handle_async_request
| resp = await self._pool.handle_async_request(req)
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/httpcore/_async/connection_pool.py", line 256, in handle_async_request
| raise exc from None
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/httpcore/_async/connection_pool.py", line 236, in handle_async_request
| response = await connection.handle_async_request(
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| pool_request.request
| ^^^^^^^^^^^^^^^^^^^^
| )
| ^
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/httpcore/_async/connection.py", line 101, in handle_async_request
| raise exc
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/httpcore/_async/connection.py", line 78, in handle_async_request
| stream = await self._connect(request)
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/httpcore/_async/connection.py", line 124, in _connect
| stream = await self._network_backend.connect_tcp(**kwargs)
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/httpcore/_backends/auto.py", line 31, in connect_tcp
| return await self._backend.connect_tcp(
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| ...<5 lines>...
| )
| ^
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/httpcore/_backends/anyio.py", line 113, in connect_tcp
| with map_exceptions(exc_map):
| ~~~~~~~~~~~~~~^^^^^^^^^
| File "/usr/lib/python3.14/contextlib.py", line 162, in __exit__
| self.gen.throw(value)
| ~~~~~~~~~~~~~~^^^^^^^
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/httpcore/_exceptions.py", line 14, in map_exceptions
| raise to_exc(exc) from exc
| httpcore.ConnectError: All connection attempts failed
|
| The above exception was the direct cause of the following exception:
|
| Traceback (most recent call last):
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/mcp/client/streamable_http.py", line 565, in handle_request_async
| await self._handle_post_request(ctx)
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/mcp/client/streamable_http.py", line 340, in _handle_post_request
| async with ctx.client.stream(
| ~~~~~~~~~~~~~~~~~^
| "POST",
| ^^^^^^^
| ...<2 lines>...
| headers=headers,
| ^^^^^^^^^^^^^^^^
| ) as response:
| ^
| File "/usr/lib/python3.14/contextlib.py", line 214, in __aenter__
| return await anext(self.gen)
| ^^^^^^^^^^^^^^^^^^^^^
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/httpx/_client.py", line 1583, in stream
| response = await self.send(
| ^^^^^^^^^^^^^^^^
| ...<4 lines>...
| )
| ^
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/httpx/_client.py", line 1629, in send
| response = await self._send_handling_auth(
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| ...<4 lines>...
| )
| ^
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/httpx/_client.py", line 1657, in _send_handling_auth
| response = await self._send_handling_redirects(
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| ...<3 lines>...
| )
| ^
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/httpx/_client.py", line 1694, in _send_handling_redirects
| response = await self._send_single_request(request)
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/httpx/_client.py", line 1730, in _send_single_request
| response = await transport.handle_async_request(request)
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/httpx/_transports/default.py", line 393, in handle_async_request
| with map_httpcore_exceptions():
| ~~~~~~~~~~~~~~~~~~~~~~~^^
| File "/usr/lib/python3.14/contextlib.py", line 162, in __exit__
| self.gen.throw(value)
| ~~~~~~~~~~~~~~^^^^^^^
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/httpx/_transports/default.py", line 118, in map_httpcore_exceptions
| raise mapped_exc(message) from exc
| httpx.ConnectError: All connection attempts failed
+---------------- 2 ----------------
| Traceback (most recent call last):
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/mcp/client/streamable_http.py", line 670, in streamable_http_client
| yield (
| ...<3 lines>...
| )
| GeneratorExit
+------------------------------------
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/mcp/client/streamable_http.py", line 647, in streamable_http_client
async with anyio.create_task_group() as tg:
~~~~~~~~~~~~~~~~~~~~~~~^^
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/_backends/_asyncio.py", line 789, in __aexit__
if self.cancel_scope.__exit__(type(exc), exc, exc.__traceback__):
~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/_backends/_asyncio.py", line 461, in __exit__
raise RuntimeError(
...<2 lines>...
)
RuntimeError: Attempted to exit cancel scope in a different task than it was entered in
an error occurred during closing of asynchronous generator <async_generator object stdio_client at 0x7f7f39edb570>
asyncgen: <async_generator object stdio_client at 0x7f7f39edb570>
+ Exception Group Traceback (most recent call last):
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/_backends/_asyncio.py", line 783, in __aexit__
| raise BaseExceptionGroup(
| "unhandled errors in a TaskGroup", self._exceptions
| ) from None
| BaseExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
+-+---------------- 1 ----------------
| Traceback (most recent call last):
| File "/home/tom/.platformio/penv/lib/python3.14/site-packages/mcp/client/stdio/__init__.py", line 189, in stdio_client
| yield read_stream, write_stream
| GeneratorExit
+------------------------------------
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/mcp/client/stdio/__init__.py", line 183, in stdio_client
anyio.create_task_group() as tg,
~~~~~~~~~~~~~~~~~~~~~~~^^
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/_backends/_asyncio.py", line 789, in __aexit__
if self.cancel_scope.__exit__(type(exc), exc, exc.__traceback__):
~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/tom/.platformio/penv/lib/python3.14/site-packages/anyio/_backends/_asyncio.py", line 461, in __exit__
raise RuntimeError(
...<2 lines>...
)
RuntimeError: Attempted to exit cancel scope in a different task than it was entered in
Version and model info
No response