> I'm stuck on how to handle upgrades though...

I've satisfied myself with the solution mentioned in #bea86499-824e-4e77-b085-2d581fa9ccab/1100c966-9671-4bc6-8b68-6d408a910da1/bd1207ef-f97e-4078-8c5d-046072012082#,
namely, upgrading on disk the way we've always done, and not
supporting on-the-fly upgrading at all.  This isn't important for this
bug, but I didn't want to just ignore that part of the commit message.