Cullen Walsh focused on infrastructure and feature development across several Facebook repositories, including fboss, CacheLib, fbthrift, and dotslash. He updated Docker base images for Ubuntu and Fedora to standardize CI environments, streamlined the zlib build process, and improved Rust script dependency formatting to enhance build reliability and release automation. In the dotslash repository, Cullen expanded artifact management by implementing support for .bz2 and .tar.bz2 compression formats using Rust and compression algorithms, increasing compatibility with common workflows. His work demonstrated depth in cross-repo tooling, containerization, and file handling, contributing to more predictable releases and robust software development practices.