auditRetention() reads the retention of the audit log (read-only with the API key; it is set with a wallet signature in the
console). auditVerifyKept(day, bytes) checks an export you kept against the day we hold or against the tombstone a deleted day
left (its digest), hashing your bytes locally. The client no longer follows redirects: fetch followed them and carried the
x-api-key header to whatever host a Location named; a 3xx is now an AereCloudError with its status.
