Update comment for standby executor

Author: rkannan82

service/history/api/respondworkflowtaskcompleted/workflow_task_completed_handler.go

@@ -666,6 +666,7 @@ func (handler *workflowTaskCompletedHandler) handleCommandRequestCancelActivity(
 			handler.activityNotStartedCancelled = true
 		} else if ai.StartedEventId != common.EmptyEventID {
 			// Activity has started - create cancel task and send to worker via Nexus.
+			// TODO: Batch tasks for the same control queue.
 			if err := handler.mutableState.AddCancelActivityNexusTasks(ai.ScheduledEventId); err != nil {
 				return nil, err
 			}

service/history/transfer_queue_standby_task_executor.go

@@ -109,7 +109,8 @@ func (t *transferQueueStandbyTaskExecutor) Execute(
 	case *tasks.ChasmTask:
 		err = t.executeChasmSideEffectTransferTask(ctx, task)
 	case *tasks.CancelActivityNexusTask:
-		// Cancel activity nexus task is best-effort and only processed in active cluster
+		// Nexus operation is synchronous. So if the failover happens waiting for the Nexus response,
+		// the task will be retried in standby.
 		err = nil
 	default:
 		err = errUnknownTransferTask