> Ah, so this was not the log of a chroot build, right?  (There’s no
> /homeless-shelter directory in the chroot.)

I'm puzzled.  The manual says that "each build process is run in a
chroot environment." [1]  However, I see

export HOME="/homeless-shelter"

in '/tmp/nix-build-coreutils-8.21.drv-7/environment-variables'.

Is anything wrong with Guix, or is it my fault?

Note that I was able to build a previous version (8.20) of Coreutils.

> Not sure what --userspec is.

'chroot --userspec=USER:GROUP' allows to specify a user and a group.

[1] https://gnu.org/software/guix/manual/guix.html#Invoking-guix_002ddaemon