Why this exists
Everyone who has run infrastructure long enough has the same story. The backup job was green for months. The cron mail said success. Then a disk died, the restore started, and somewhere in the middle: a checksum error, a missing pack file, a snapshot that referenced data that wasn't there anymore. The backups had been broken for weeks, and every tool in the chain had honestly reported that its own step "worked."
The fix has been known forever: test your restores. Almost nobody does, because it's manual, boring, and always loses to more urgent work. Vestal's job is to make verified backups the path of least resistance: one line in the job you already run, agents that do the tedious verification properly, and an alarm system that treats silence with the suspicion it deserves.