I.e. just what would be done by adding /repo to pacman.conf and removing its files (and updating its repo.db) after a successful librerelease?

mtjm: yes, exactly that. I don't think fauno realized what /repo was.

So we need to work out a way to automagically add "file:///repo" to pacman.conf in the chroot.

Is there any need to customize pacman.conf in the chroot, other than to install dependencies of packages to build from repos like pcr (and to disable CheckSpace)? Automatically writing a new pacman.conf would be simpler.

devtools has a different pacman.conf that it inserts depending on what repo you are building for, but we've typically rejected that approach. I mentioned going to that once on IRC, but every one was pretty against that, saying KISS.

Do we have any rational arguments against using fixed libretools-provided makepkg.confs and pacman.confs? It would help make builds more predictable.

mtjm: no real arguments that I've heard.

However, automatically adding "file:///repo" to pacman.conf is now (in git) done automatically by libremakepkg, so this task done.