Easier said than done in this case. Actually effective crosschecks preventing this issue from occurring would entail rather massive I/O and CPU amplification in common operations.

we could have run with https://www.postgresql.org/docs/current/app-pgchecksums.html turned on, but it slows things down a bunch - and turning it on in retrospect would have taken days. Also not clear that it would have caught whatever the underlying corruption was here…