Moving domain registrars. I'm an old hand at this. Except I forgot that I built a one-page website using my old registrar's "site builder" tool that even they discontinued (and so I couldn't update).
So... I had to find the old version on the Internet Archive, view enough of the source to realize it was awful, got a freebie web template from the folks at HTML5 UP, fought with HTML today which was a welcome distraction and now my moss-enthusiast one-pager is live again!