Python: MCP stdio shutdown raises anyio cancel-scope error in agent_framework MCPStdioTool

[jspv]

Issue: Launching an MCP stdio server via agent_framework.MCPStdioTool works (server responds to ListTools/CallTool), but teardown crashes the stdio client. The error appears after the tool has responded:

an error occurred during closing of asynchronous generator stdio_client…
RuntimeError: Attempted to exit cancel scope in a different task than it was entered in

Expected: stdio MCP starts, responds, and shuts down without exceptions.
Actual: stdio shutdown raises the anyio cancel-scope error, causing the agent run to fail after the MCP server has already responded.

Steps to reproduce (minimal code provided) - the sample uses a provided basic standalone mcp, but you can use any stdio mcp and the issue occurs.

agent-framework-core = 1.0.0b251211

"""
Agent Framework repro: stdio MCP shutdown using local_mcp_server.py.

Starts the bundled stdio MCP server (scripts/local_mcp_server.py) via MCPStdioTool
and runs a single prompt to trigger startup/shutdown.
"""

from __future__ import annotations

import asyncio
import os
import sys
from pathlib import Path

from agent_framework import ChatAgent, MCPStdioTool, ai_function
from agent_framework.openai import OpenAIChatClient


@ai_function
def ping() -> str:
    return "pong"


async def main() -> None:
    server_path = Path(__file__).resolve().parent / "local_mcp_server.py"

    sample_tool = MCPStdioTool(
        name="sample_local_mcp",
        command=sys.executable,
        args=[str(server_path)],
        env={"LOG_LEVEL": "warning"},
    )

    client = OpenAIChatClient(
        model_id="gpt-4o-mini",
        api_key=os.environ["OPENAI_API_KEY"],
    )

    agent = ChatAgent(
        chat_client=client,
        tools=[sample_tool, ping],
        instructions="Trigger MCP startup/shutdown via stdio.",
    )

    try:
        await agent.run(messages="hi", store=False)
    except Exception as exc:  # noqa: BLE001
        raise RuntimeError(f"Agent run failed: {type(exc).__name__}: {exc}") from exc


if __name__ == "__main__":
    asyncio.run(main())

local_mcp_server.py (or use your own)

"""
Minimal MCP stdio server exposing a single `ping` tool.
"""

from __future__ import annotations

import asyncio

from mcp import types
from mcp.server.lowlevel import Server
from mcp.server.models import InitializationOptions
from mcp.server.stdio import stdio_server
from mcp.shared.exceptions import McpError


async def main() -> None:
    server = Server("sample_local_mcp")

    @server.list_tools()
    async def list_tools() -> list[types.Tool]:
        return [
            types.Tool(
                name="ping",
                description="Return pong.",
                inputSchema={
                    "type": "object",
                    "properties": {},
                    "additionalProperties": False,
                },
            )
        ]

    @server.call_tool()
    async def call_tool(request: types.CallToolRequest) -> list[types.TextContent]:
        if request.params.name != "ping":
            raise McpError(f"Unknown tool: {request.params.name}")
        return [types.TextContent(type="text", text="pong")]

    async with stdio_server() as (read_stream, write_stream):
        await server.run(
            read_stream,
            write_stream,
            initialization_options=InitializationOptions(
                server_name="sample_local_mcp",
                server_version="0.0.1",
                capabilities=types.ServerCapabilities(
                    tools=types.ToolsCapability(),
                ),
            ),
            raise_exceptions=True,
        )


if __name__ == "__main__":
    asyncio.run(main())

[jspv]

The problem might be related to modelcontextprotocol/python-sdk#521 and this note in the haystack mcp implementation: https://docs.haystack.deepset.ai/reference/integrations-mcp (step 4)

[moonbox3]

Should be handled in #3277