Okay, I got some help from #nonguix on Libera, turns out, the System Crafters install image I was using pinned the nonguix channel to a specific commit, and that commit was either broken or had an implicit dependency on the stock guix channel which caused breakage.
Removed the pin and I was able to reconfigure the system. This took several hours, since it downloaded hundreds of megs of... something... and compiled the whole Linux kernel.
But, I have a caps lock key that works like control, which means I can type on this laptop without immediately becoming enraged.
I am not sure it should be so difficult to change one keyboard layout setting.