bug#74534: [shepherd] guix-home managed shepherd shares process group with shell

[Jelle Licht]

Cc'ing Tomas and Ludo, as they actually diagnosed the issue [0].

The user shepherd, as configured using guix home, runs under the same
process group as the shell that initially triggered guix home's
"$HOME/.guix-home/on-first-login" script.

This leads to the user shepherd receiving signals that are sent to the
shell, such as a SIGINT/^C, and subsequently stopping entirely.

If I understand the fine folks on IRC correctly, the daemonize action of
the root-service in shepherd is missing a call to (setsid). I am
uncertain whether this setsid call should be made conditional or not.

Kind regards,
Jelle Licht

[0]: https://logs.guix.gnu.org/guix/2024-11-25.log#172506