A ledger position suitable for anchoring outside the audit database.

Persist this value in a system with a separate trust boundary—for example immutable object storage, a transparency service, or a monitoring account.

This is the only defence the library has against wholesale rollback. A chain proves its own internal consistency, and an attacker who truncates the ledger at some sequence and rewrites forward from there satisfies that perfectly. Comparing the live head against a position recorded somewhere they do not control is what turns "consistent" into "complete". Stored inside the audit database, a checkpoint proves nothing, because it falls to the same attacker in the same breath.