$ sudo ./pre-inst-env guix archive --generate-key
$ ./pre-inst-env guix archive --export hello > hello.nar
error: executing `guix-authenticate': No such file or directory
guix archive: error: build failed: program `guix-authenticate' failed with exit code 1

The command succeeded when I installed Guix and re-ran it without
‘./pre-inst-env’.

Slightly off-topic: is Hydra supposed to do the same when someone
requests a substitute?

Also, where can I find the corresponding NAR info file?  According to
this commit [1], the signature should be there.

[1] https://github.com/NixOS/nix/commit/0fdf4da0e979f992db75cc17376e455ddc5a96d8