Rationale
Every line of the append-only ledger is a well-formed event; the one durable record nothing else can reconstruct stays readable.
Required behaviour
Every line of the append-only ledger is a well-formed event.
Failure behaviour
A violation is a FAIL finding under the category records, and the command that found it exits 10. Under watch the same violation is reported as drift and the command exits 11.
Verification
mj_validate_ledger decides it, dispatched from check, doctor, watch. The behavioural case test/cases/22_history.sh proves it, and CI runs that case.