Cullen Walsh focused on infrastructure and feature development across several Facebook repositories, including fboss, CacheLib, fbthrift, and dotslash. He improved build reliability and release automation by updating Docker base images for Ubuntu and Fedora, standardizing CI environments, and streamlining the zlib library build process using CMake and Rust. In dotslash, Cullen expanded artifact management by implementing support for .bz2 and .tar.bz2 compression formats, enhancing compatibility with common workflows. His work emphasized cross-repo tooling consistency and robust deployment scripts on Linux, resulting in more predictable releases. The engineering demonstrated depth in build systems, containerization, and compression algorithm integration.