Update: it’s mostly fixed now, though there remain a couple little weirdnesses to sort out. I’ve learned two lessons from this: 1) backups and 2) child themes.
I just updated a bunch of stuff on this site, including my theme. And remembered moments too late that I’ve made some customizations to the theme.
Which are now gone.
(For instance, right now, the Fiction links don’t work. I’ll get them working again soon, though.)