Revert voided the fact row and left the vector, so recall kept serving the
voided fact's utterance and the documented repair reported success on a box that
stayed broken. There was no way to repair a poisoned box at all.
DeletePrefix covers every vector for the key, earlier rows included: their values
are superseded, and a superseded value has no business claiming a turn. It is
best-effort — the audit trail is already committed, and a fact that is voided but
still recallable beats a void that failed.
