How to scuttle your Gnome desktop without hardly trying, and how to recover

Not entirely positive, but possibly what brought the whole thing down was uninstalling a package which was blocking upgrades (and could not be fixed, sudo apt --fix-broken install libwacom9 also failed):

$ sudo apt remove libwacom9

That seemed fine.

sudo apt update && sudo apt upgrade && sudo apt dist-upgrade

Running the upgrades seemed fine, except that while they were running, the screen lock came up— and trying to log back in through the GUI was a complete nonstarter.

Not sure if this was