Confirmed on the test laptop's real install: /etc/snapper/configs/ was
completely empty post-install — snapper create-config failed silently and
BOS's advertised snapshot/rollback feature was entirely non-functional,
despite snapper-cleanup.timer being enabled and grub-btrfsd active (both
harmless no-ops with no config to act on).
Root cause is the known chroot-specific busy-mount race already documented
in this section's comments, but the existing recovery (retry umount 5x,
then one lazy-unmount fallback) wasn't sufficient on this hardware — a
lazy unmount detaches the mountpoint from the namespace immediately, but
whatever was holding it busy can take a moment longer to actually release,
and the immediately-following rmdir/create-config both fail if anything
still references /.snapshots at that instant.
Wrap the entire unmount → rmdir → create-config → cleanup → remount
sequence in an outer retry loop (checking whether the config file actually
exists before each attempt and after the loop), add a settle delay after
the lazy-unmount fallback, and turn the final failure into a loud ERROR
instead of a warning that's easy to miss — a system silently shipping
without snapshots is worse than one that's slow to set them up.
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