code: func ActivateExecution(c context.Context, auth *dm.Execution_Auth, actToken []byte) (a *Attempt, e *Execution, err error) {
  	a, e, err = verifyExecutionAndActivate(c, auth, actToken)
  	if err != nil {
  		logging.Fields{ek: err, "eid": auth.Id}.Errorf(c, "failed to activate execution")
  		err = makeError(err, "failed to activate execution Auth")
  	}
  	return a, e, err
  }
docs: // ActivateExecution validates that the execution is unactivated and that
  // the activation token matches and then sets the token to the new
  // value.
  //
  // It's OK to retry this. Subsequent invocations with the same Token
  // will recognize this case and not return an error.