During June 2025, John Cahill developed Docker registry integration for Buck rules in the facebook/buck2-prelude repository, focusing on build system configuration using Starlark. He introduced the fetch_image_from_registry Buck rule, enabling automated retrieval of Docker images from an internal registry for use in Antlir images and fbpkgs. By adding the uses_docker_registry label to genrule_local_labels.bzl, John streamlined the process of sourcing trusted images, enhancing build automation and reproducibility. His work reduced manual provisioning steps and improved pipeline reliability, demonstrating depth in build system design and Starlark scripting while addressing security and consistency requirements in complex build environments.