fix: catch KeyboardInterrupt in FastMCP.run() for clean Ctrl+C exit

When running a stdio server from the terminal, Ctrl+C previously produced
a noisy multi-frame traceback through anyio.run() → asyncio.runners →
anyio.streams.memory.receive. This change catches KeyboardInterrupt at
the top-level run() method so the server exits quietly, matching user
expectations for a terminal application.

Closes #2663

Co-Authored-By: Claude <noreply@anthropic.com>

Author: kaXianc2-gom

src/mcp/server/mcpserver/server.py

@@ -291,13 +291,18 @@ def run(
         if transport not in TRANSPORTS.__args__:  # type: ignore  # pragma: no cover
             raise ValueError(f"Unknown transport: {transport}")
 
-        match transport:
-            case "stdio":
-                anyio.run(self.run_stdio_async)
-            case "sse":  # pragma: no cover
-                anyio.run(lambda: self.run_sse_async(**kwargs))
-            case "streamable-http":  # pragma: no cover
-                anyio.run(lambda: self.run_streamable_http_async(**kwargs))
+        try:
+            match transport:
+                case "stdio":
+                    anyio.run(self.run_stdio_async)
+                case "sse":  # pragma: no cover
+                    anyio.run(lambda: self.run_sse_async(**kwargs))
+                case "streamable-http":  # pragma: no cover
+                    anyio.run(lambda: self.run_streamable_http_async(**kwargs))
+        except KeyboardInterrupt:
+            # Ctrl+C should exit cleanly without a traceback when running
+            # a server from the terminal (e.g. stdio transport).
+            pass
 
     async def _handle_list_tools(
         self, ctx: ServerRequestContext[LifespanResultT], params: PaginatedRequestParams | None

tests/server/test_stdio.py

@@ -169,3 +169,20 @@ async def lifespan(server: MCPServer) -> AsyncIterator[None]:
     assert events == ["setup", "cleanup"]
     response = jsonrpc_message_adapter.validate_json(captured.getvalue().decode().strip())
     assert response == JSONRPCResponse(jsonrpc="2.0", id=1, result={})
+
+
+def test_mcpserver_run_catches_keyboard_interrupt(monkeypatch: pytest.MonkeyPatch) -> None:
+    """Ctrl+C during `run()` should exit cleanly without a traceback.
+
+    Regression test for #2663: when running a stdio server from the terminal,
+    KeyboardInterrupt (Ctrl+C) should not produce a multi-frame traceback
+    through anyio.run() → asyncio.runners.
+    """
+
+    def mock_anyio_run(*args: object, **kwargs: object) -> None:
+        raise KeyboardInterrupt()
+
+    monkeypatch.setattr(anyio, "run", mock_anyio_run)
+
+    # Should not raise — KeyboardInterrupt is caught inside run()
+    MCPServer(name="KeyboardInterruptServer").run("stdio")