FastMCP.run(transport="stdio") produces noisy traceback on KeyboardInterrupt instead of clean exit

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

Running a FastMCP stdio server from the terminal and interrupting with Ctrl-C produces a multi-frame traceback through anyio.run() → asyncio.runners → mcp.server.lowlevel.server.run → anyio.streams.memory.receive. The server is correctly waiting on stdin in an async loop; the trace surfaces because anyio/asyncio don't suppress the cancellation chain. Suggested fix: catch KeyboardInterrupt (or asyncio.CancelledError at the outer boundary) inside FastMCP.run and exit cleanly. Cosmetic but reduces user confusion when testing MCP servers from the terminal.

Example Code

Python & MCP Python SDK

Python 3.13.5
MCP Python SDK 1.27.1

首先重现 FastMCP stdio 服务器的 Ctrl-C 行为，然后跟踪 FastMCP.run 经过 mcp.server.lowlevel.server.run 以及 anyio 内存接收路径的过程。修复完成的标准是：中断服务器时能够干净地退出且不出现 traceback，同时正常的关闭行为保持不变。