Janus focused on restoring and stabilizing package compatibility within large-scale Haskell build systems, working on the simonmichael/stackage and commercialhaskell/lts-haskell repositories. He addressed build system configuration issues by removing exclusion and version constraints in YAML-based build matrices, which re-enabled the dimensional, geodetics, and dhall packages for standard builds and continuous integration. His approach involved careful updates to build-constraints and validation within the main build matrix, ensuring reliable package inclusion and reducing the risk of broken builds for downstream dependencies. Janus demonstrated depth in build system configuration and YAML, contributing to the robustness and maintainability of the release pipelines.