Hello!
I'm happy to report this was due to mis-configuration on my part. More
specifically, it it was missing the xorg-configuration modification bit,
which is documented. Testing in a VM using the following, modified
configuration cannot reproduce the problem:
--8<---cut here--
Hello!
I based my operating system configuration on
gnu/system/examples/desktop.tmpl in the Guix tree, and was surprised
that my dvorak keyboard is in effect everywhere except at the GDM
greeter screen (where it is QWERTY).
Here's the full config:
--8<---cut here---start-