cutover.md is the reasoning and is too long to read at 2am. This is the
same sequence as commands, for this install: eight mailboxes, two people
and a printer.
That scale settles three things the general plan leaves open. The store is
small enough that the two-pass rsync buys nothing, so it is one cp inside
the window and a simpler sequence when it matters. "Every account still
works" is two sign-ins. And a reboot inside the window is affordable, which
is the only honest proof that the fork comes up on boot and the old unit
does not — is-enabled says what is configured, a reboot says what happens.
The rollback leads with chattr -i, because step 7's guard stops the
Enterprise build exactly as it stops the fork, and finding that out during
a rollback costs the worst ten minutes of the night.
And it names the printer as its own check. It is the one user that cannot
report a fault: a hardcoded credential and an old TLS stack, of the kind a
stricter default quietly refuses. The people will phone; the printer will
just stop, and nobody will notice for a fortnight.
