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

まず FastMCP の stdio サーバーでの Ctrl-C の動作を再現し、次に mcp.server.lowlevel.server.run と anyio のメモリ受信パスを通る FastMCP.run を追跡します。サーバーを割り込みしたときに traceback なしで正常に終了し、通常のシャットダウン動作が変わらなければ修正完了です。