Even nicer could be using 'guix repl' in the teams.scm script shebang.
This way even for those using it outside of 'git send-email', it'd
always work.

I can't find a nice solution to do that. And I think people who run teams.scm directly will expect a guile crash and make sure to get the correct environment, so it's not really a problem at that point.

This is not the case for people who run `git send-email`. Those people don't expect a guile crash.

So if you have a clean solution that works in a shebang (without the file being detected as a shell script by most editors), please show it :-)