fix(go): repair migration wire contracts and runtime lifecycle; document incomplete port

pkg/protocol/handshake.go

@@ -20,6 +20,9 @@ func HandleHandshake(conn net.Conn) (*chacha8.UxChaCha8, *chacha8.UxChaCha8, err
 	if err != nil {
 		return nil, nil, err
 	}
+	if frame.Mode != 0x01 {
+		return nil, nil, errors.New("invalid handshake frame mode")
+	}
 	if len(frame.Payload) < 20 {
 		return nil, nil, errors.New("client handshake too short")
 	}