Yes, that is the commit I'm talking about.
And, yes it is possible for bin/arch --wipe to break saved URLs/external
One way in which this can happen is if the cumulative mailbox file
(archives/private/<listname>.mbox/<listname>.mbox) has unescaped "From "
lines in message bodies. This will only be the case with .mbox files that
are 'old' (maybe older than 2.1.x, but I'm not sure) or imported from
another application. The bin/cleanarch script can help find and fix such
I think there are other ways in which this can happen too, but I'm not
sure what they are, but I am confident that if Mailman isn't running when
you do the bin/arch --wipe, the message numbers in the new archive will get
assigned in mbox order, so the issue is if the original numbers somehow are
not in mbox order.
One thing you can do is stop Mailman, make a backup copy of the
archives/private/<listname>/ directory, run bin/arch --wipe <listname> and
then quickly check sample messages throughout the new and backup archives
to verify they have the same message numbers. If they do, just start
Mailman, If not, restore the backup.
Note that the current plan is to redesign the built-in archiver for
Mailman 3.0 to avoid this problem in the future among other things.