Revert agent edits to the managed onboarding-name memory block.
Guards the managed onboarding-name block in a fixed set of memory files. A
write_file/edit_file that leaves the managed block untouched passes
through; one that alters or drops it has the block restored (other edits
kept) and returns an error. If the restore itself fails, an error is still
returned so the failure is never silent.
