code: func (e *engineImpl) GetInvocation(c context.Context, job *Job, invID int64) (*Invocation, error) {
  	// Note: we want public API users to go through GetVisibleJob to check ACLs,
  	// thus usage of *Job, even though JobID string is sufficient in this case.
  	return e.getInvocation(c, job.JobID, invID)
  }
docs: // GetInvocation returns some invocation of a given job.
  //
  // Part of the public interface.