> Use specification->package+output.

I tried that, and it indeed doesn't complains about 'unknown package'
anymore. However, send-email is still not installed after a system
reconfigure:

--8<---------------cut here---------------start------------->8---
$ sudo guix system reconfigure guix.scm
...
$ git send-email *.patch
git: 'send-email' is not a git command. See 'git --help'
--8<---------------cut here---------------end--------------->8---

What am I missing here?

I've attached the full file to make it clearer.