The record

What was done, when, by which commit.

Each line is a record; its hash covers everything in it and the hash of the line before.

seqat (UTC)actioncommithash
What this proves

That the record has not been rewritten. Not that it was true.

A verified journal proves each record existed in exactly this form no later than the time its block was anchored, and that nothing has been inserted, removed or edited since. Two unrelated authorities are used so that distrusting one does not dismiss the record. It does not prove a record was true when written; a journal is an honest diary, not a witness. What anchoring removes is the possibility that the diary was rewritten afterwards.

RECORD

Hash-chained

SHA-256 over a canonical form of the record, including the previous record's hash. Edit one field and its hash, and every later link, breaks.

BLOCK

Merkle-rooted

Records are closed into blocks; each header commits to the block before it. One root stands for everything beneath it.

ANCHOR

Two authorities

Each root is signed by a timestamping authority and committed to Bitcoin. Rewriting the past would need both to cooperate, backwards in time.

Want this for your own agents? The attestation service keeps a journal like this one for them, appended over HTTPS and anchored the same way; the verifier and the journal format are open source, and the readiness check is where an engagement starts.