code: func (e *engineImpl) execCronTickTask(c context.Context, tqTask proto.Message) error {
  	msg := tqTask.(*internal.CronTickTask)
  	return e.jobTxn(c, msg.JobId, func(c context.Context, job *Job, isNew bool) error {
  		if isNew {
  			logging.Errorf(c, "Scheduled job is unexpectedly gone")
  			return errSkipPut
  		}
  		logging.Infof(c, "Tick %d has arrived", msg.TickNonce)
  		return pokeCron(c, job, e.cfg.Dispatcher, func(m *cron.Machine) error {
  			// OnTimerTick returns an error if the tick happened too soon. Mark this
  			// error as transient to trigger task queue retry at a later time.
  			return transient.Tag.Apply(m.OnTimerTick(msg.TickNonce))
  		})
  	})
  }
docs: ////////////////////////////////////////////////////////////////////////////////
  // Cron handling.
  // execCronTickTask corresponds to a delayed tick emitted by a cron state
  // machine.