Introduce some form of “oldest commit offset that can be replayed” metric for shards. That, combined with the existing commit offset, can be used to determine:
This assumes software would always perform incremental sync and that is not always true. It may be best to not expose a minimum offset for such software (suspect most of them would not have such a metric at all) and consider software that does not expose such metric to be one that does not replay when a node re-joins.