I have a 13.1 system with all the latest updates as of today and it is spitting
out the

  UNEXPECTED INCONSISTENCY; RUN fsck MANUALLY

message for the root filesystem, and then booting normally with root mounted
root read-write.

First of all, I would expect it to not boot normally in this case, but
whatever.

Anyway, when I try to do what it says, it's impossible!

Here's why: even though I reboot with "single ro" on the boot line and it does
in fact go into single user mode, it still mounts root read-write (after
complaining of the same fsck errors).

Since the 1980's single user mode has always left root mounted read-only so you
can run fsck if needed, and you can always remount it read-write if you want.
Why did this change?

Of course "mount -o remount,ro /" doesn't work.

Because root is mounted read-write and it's impossible to get the system to
boot with root mounted read-only, then even in single user mode, it's
impossible to run fsck and fix the problem.

So it's impossible to resolve this problem without the use of a rescue disk.

Please fix, this is a bad dead-end people can fall into.