code: func (ctl *taskController) PrepareTopic(ctx context.Context, publisher string) (topic string, token string, err error) {
  	return ctl.eng.prepareTopic(ctx, &topicParams{
  		jobID:     ctl.JobID(),
  		invID:     ctl.InvocationID(),
  		manager:   ctl.manager,
  		publisher: publisher,
  	})
  }
docs: // PrepareTopic is part of task.Controller interface.