private StreamTask convertStandbyToActive(final StandbyTask standbyTask, final Set<TopicPartition> partitions) {
        return activeTaskCreator.createActiveTaskFromStandby(standbyTask, partitions, mainConsumer);
    }
@throws TaskMigratedException if the task producer got fenced (EOS only)
@throws StreamsException fatal error while creating / initializing the task

public for upgrade testing only
streams/src/main/java/org/apache/kafka/streams/processor/internals/TaskManager.java