Dynamic MCP Toolset | ValueError: MCPServer.__aexit__ called more times than __aenter__ #3542
Description
Initial Checks
- I confirm that I'm using the latest version of Pydantic AI
- I confirm that I searched for my issue in https://github.com/pydantic/pydantic-ai/issues before opening this issue
Description
I am trying to have a single agent configuration for my users that uses an authenticated MCP server. Following the documentation I see I can pass in a function to use the RunContext to configure the MCP server for each user.
This correctly authenticates each MCP server and returns the results, but it always errors out before completing. I can see in the events that when prompts "what's my github username?" it gets the logged in user, then afterwards it fails with the below error.
File "C:\Users\user\AppData\Local\Programs\Python\Python313\Lib\contextlib.py", line 235, in __aexit__
await self.gen.athrow(value)
File "C:\Users\user\cheersgpt\.venv\Lib\site-packages\pydantic_ai\agent\__init__.py", line 656, in iter
async with toolset:
^^^^^^^
File "C:\Users\user\cheersgpt\.venv\Lib\site-packages\pydantic_ai\toolsets\combined.py", line 60, in __aexit__
await self._exit_stack.aclose()
File "C:\Users\user\AppData\Local\Programs\Python\Python313\Lib\contextlib.py", line 705, in aclose
await self.__aexit__(None, None, None)
File "C:\Users\user\AppData\Local\Programs\Python\Python313\Lib\contextlib.py", line 768, in __aexit__
raise exc
File "C:\Users\user\AppData\Local\Programs\Python\Python313\Lib\contextlib.py", line 751, in __aexit__
cb_suppress = await cb(*exc_details)
^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\user\cheersgpt\.venv\Lib\site-packages\pydantic_ai\toolsets\_dynamic.py", line 44, in __aexit__
return await self._toolset.__aexit__(*args)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\user\cheersgpt\.venv\Lib\site-packages\pydantic_ai\mcp.py", line 650, in __aexit__
raise ValueError('MCPServer.__aexit__ called more times than __aenter__')Example Code
from fastapi import Depends
from pydantic_ai import Agent, RunContext
async def github_mcp(ctx: RunContext[AgentContext]):
token = ctx.deps.user.metadata.github_access_token
return MCPServerStreamableHTTP(
id="github",
url="https://api.githubcopilot.com/mcp/",
headers={"Authorization": f"Bearer {token}"},
)
github_agent = github_agent = Agent(TestModel(), deps_type=AgentContext, toolsets=[github_mcp])
@app.post("/stream")
async def stream(
body: StreamRequest,
user: User = Depends(get_current_user),
):
agent_context = AgentContext(user=user)
async for event in github_agent.run_stream_events(body.prompt, deps=agent_context):
# await event_handler.handle(event)
print(event)Python, Pydantic AI & LLM client version
Python: 3.13.2
Pydantic AI: 1.22.0
LLM: OpenAI (latest)