In server mode, everything is recorded in an append-only log where each entry includes a hash of the previous one, so removing or altering an entry breaks the chain visibly. The log is also shipped off the machine continuously, so an attacker who takes over the server cannot quietly rewrite history that has already left.
It answers, without anyone holding a decryption key: who was granted which vault and when, who revoked whom, which principals held file custody in a protected vault on a given date, which secrets were rotated by which worker, and every failed authentication.
Your client also audits itself: it fetches the entries covering its own recent activity and checks that everything it did appears, and that nothing it did not do appears under its name. A mismatch is the strongest signal available that something is wrong with the server, and doctor runs the check for you.
In serverless mode there is no read log
Nobody is in the loop when you decrypt a file on your own machine, so nothing can record it. You get a complete, signed record of every change (every grant, revocation and new version) and no record of reads at all. If read auditing is a hard requirement for you, run the server.