code: func dummyServicePrelude(c context.Context, methodName string, req proto.Message) (context.Context, error) {
  	return nil, grpcutil.Errf(codes.FailedPrecondition,
  		"This pRPC endpoint cannot be handled by the default service. It should have been routed to the "+
  			"appropriate service via dispatch. This error indicates that the routing is not working as intended. "+
  			"Please report this error to the maintainers.")
  }
docs: // dummyServicePrelude is a service decorator prelude that always returns
  // "codes.FailedPrecondition".
  // This is implemented this way so that the decorated service can be made
  // discoverable without actually hosting an implementation of that service.
  // The actual implementation is hosted in a separate GAE service, and RPCs
  // directed directed at this dummy service should be automatically routed to
  // the implementing GAE service through "dispatch.yaml".