I finally got whenjobs to entirely manage the libguestfs release process (still to do: stable branches, testing on anything except Fedora).
It is triggered by tagging a version in git, whereupon the script takes over, building a tarball, testing the tarball, pushing it to the website, and kicking off a build in Rawhide.
So far it’s been a success, to some degree. In hindsight I could probably have used incron, although that is far more ugly and would have been a real hack. Plain ol’ make might have worked too, although it would have required more babysitting.