normalize string ID to int in server messages for compatibility

Some non-standard SSE servers may return numeric IDs as strings,
even when the original request used an integer. This change ensures
that message.root.id is always an integer to maintain consistency
and avoid type issues in downstream processing.

Author: 晓明 王

src/mcp/client/sse.py

@@ -98,6 +98,21 @@ async def sse_reader(
                                             message = types.JSONRPCMessage.model_validate_json(  # noqa: E501
                                                 sse.data
                                             )
+                                            
+                                            # Normalize ID to int if it's a numeric string.
+                                            # Some non-standard SSE servers return numeric IDs as strings,
+                                            # even if the original request used an integer ID.
+                                            if isinstance(message.root, types.JSONRPCResponse):
+                                                msg_id = message.root.id
+                                                if isinstance(msg_id, str) and msg_id.isdigit():
+                                                    message.root.id = int(msg_id)
+                                                elif not isinstance(msg_id, int):
+                                                    logger.warning(
+                                                        "Ignored message with "
+                                                        f"invalid ID: {msg_id!r}"
+                                                    )
+                                                    continue
+
                                             logger.debug(
                                                 f"Received server message: {message}"
                                             )