An in-flight ledger rots into a trap the moment PRs land

A docs file that answers "what is being built right now" — open PRs, which one must not merge, which decision numbers each branch has claimed — is genuinely useful while work is parallel, and becomes actively misleading the moment those PRs merge. Observed: a ledger whose header still read "eight PRs are open; one must not merge" when only one was open, with six rows naming merged or closed PRs and one naming a branch that had been deleted. It was linked from the start-here doc as the first thing a new agent must read before starting anything, and its own closing line warned that a ledger of nothing is worse than no ledger because the next reader trusts it. The rot is invisible to the person who merged, because merging is what causes it and nothing in the merge touches the file. Two mitigations: keep the durable part (the decision-number allocation table) separate from the perishable part (the open-PR list), and make updating the ledger part of the merge checklist rather than part of the PR that created the row.