It just makes things unnecessarily complicated. We can just exit without cleaning anything up, since the only thing to do is unmark builds and build steps as busy. But we can do that by having systemd call "hydra-queue-runner --unlock" from ExecStopPost.
To start hacking on Hydra, run:
$ ./dev-shell
$ ./configure $configureFlags --prefix=/opt/hydra
$ make
$ make install
Or, if you just want to build from source (on x86_64-linux):
$ nix-build -A build.x86_64-linux release.nix
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