While setting it up to my liking, I opened Gnome Tweaks to change the Caps Lock button to be a Control key. Immediately upon changing the setting (without any other action on my part), the system locked the screen and any further efforts to log in result in the screen going blank momentarily and the lock screen being displayed.
I was unable to usefully identify the laptop based on the information at wiki.puri.sm/hw. I consulted my order information instead.
It doesn't appear to boot grub, but I'm not sure I'd know. I can reach the BIOS settings, but nothing there seems to do anything useful. As to rebooting, I did try that immediately. No change. I can log in using Ctrl+Alt+F3, as suggest, but there's no server running a display at that point. I'll be awaiting a response from Purism before I wipe my user configuration.