Rollback on Error and Conflict Resolution

Rolling back an optimistic add (remove the item) or delete (restore the item) is straightforward. Rolling back an update is more complex: you must restore the exact previous value. If the item was updated multiple times optimistically, you must track each prior value separately, not just the original server state.

Consider this scenario: the server has item at value Z. You optimistically update to X. While your request is in-flight, another user updates the same item to Y on the server. Your request arrives and the server rejects it (conflict). Your rollback target is Z, but the server's current state is Y. Restoring Z would overwrite Y incorrectly.