An additional data point: guix-daemon chowns build trees to the caller upon failure (a very handy feature) since this 2016 commit:
https://git.savannah.gnu.org/cgit/guix.git/commit/?id=2608e40988ba8cf51723fe0d21bdedf6b3997c9c The Nix build daemon, which guix-daemon is based on, did not have this feature.