Hello, This removes hydra support to use Cuirass as the only continuous integration system. It also simplifies the evaluation process. Here's how it's working now: * Cuirass fetches new commits and calls its "evaluate" process. * The "evaluate" process calls the "cuirass-jobs" procedure in the newly checkouted Guix "build-aux/cuirass/gnu-system.scm" file. * The "hydra-jobs" procedure in "build-aux/hydra/gnu-system.scm" file starts the evaluation of "hydra-jobs" of (gnu ci) module in an inferior using the new commit. * This procedure returns the list of all the package derivations at that very commit under Hydra job format. * This list is converted to the Cuirass job format and written on the stdout port. * The main Cuirass process reads the "evaluate" output using a pipe, and registers the derivation that needs to be built in database. This is quite complex and it requires to pass around a huge list of jobs, consuming a lot of memory. Here's the simplified method: * The first two steps are identical. * The "cuirass-jobs" procedure starts the evaluation of "cuirass-jobs" of (gnu ci) module in an inferior using the new commit. This procedure is passed a registration callback that directly registers the given jobs in database. It doesn't return anything. As the "register" procedure is a part of Cuirass, the inversion on control caused by the inferior is problematic. I had to proxy the registration requests from the inferior to the evaluation process using a named pipe. Other than that, the process seems now less obfuscated. Thanks, Mathieu