Going slightly crazy. I updated and built #Emacs from #git, which I hadn't done since last September. All kinds of weird behaviour. 🤔 In particular, I can no longer start up Emacs as my window manager (#exwm). Dies during initialization and --debug-init makes no difference. 😟 Serious debugging called for, I guess.
Luckily, I have #StumpWM as my backup and simply using Emacs full screen is almost as good as exwm... but not quite.