[HillRat]

To be fair -- and I'm no blockchain booster -- transactional rollbacks should be modeled as separate operations and replacement transactions on an immutable log (or loggish thing, anyway). You can use bitemporal tracking to model invalid belief states, but your system should never be allowed to drop transactions.

[prostoalex]

Yep, they generally are in modern payment systems. A chargeback is a separate transaction that has to be initiated, submitted and paid for.