Client tool call hangs forever if server crashes or connection dies when using streamable-http

Initial Checks

• I confirm that I'm using the latest version of MCP Python SDK
• I confirm that I searched for my issue in https://github.com/modelcontextprotocol/python-sdk/issues before opening this issue

Description

If the server dies during a tool call before it sends a response the client will get stuck forever.

Example Code

# server.py

from mcp.server.fastmcp import FastMCP
import sys

mcp = FastMCP("StatefulServer")

@mcp.tool()
def greet(name: str = "World") -> str:
    """Greet someone by name."""
    sys.exit(0)
    return f"Hello, {name}!"


if __name__ == "__main__":
    mcp.run(transport="streamable-http")


# client.py

import asyncio

from mcp import ClientSession
from mcp.client.streamable_http import streamablehttp_client


async def main():
    # Connect to a streamable HTTP server
    async with streamablehttp_client("http://localhost:8000/mcp") as (
        read_stream,
        write_stream,
        _,
    ):
        # Create a session using the client streams
        async with ClientSession(read_stream, write_stream) as session:
            # Initialize the connection
            await session.initialize()

            res = await session.call_tool("greet", {"name": "World"})
            print(res)


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



# Run server.py then client.py


# client.py will hang forever in the tool call and never complete. I would expect it to throw an error since the connection died and it will never get a response.

Python & MCP Python SDK

Python 3.13.7
mcp 1.20.0

Bắt đầu với entry point streamablehttp_client và đường dẫn ClientSession.call_tool được hiển thị trong client.py, sau đó tái hiện sự cố crash của server.py trong khi gọi công cụ. Hoàn thành khi client báo lỗi kết nối thay vì chờ vô thời hạn nếu server thoát trước khi phản hồi.