During October 2025, Marc Poulin focused on improving type safety in the facebook/buck2-prelude repository by addressing a type inconsistency within the test_binary module. He modified the listing_to_testnames function to return a list of binaries instead of strings, ensuring that type contracts were correctly enforced throughout the Erlang-based test framework. This adjustment reduced the risk of runtime errors and continuous integration failures, contributing to greater reliability and maintainability of Buck2 builds. Marc applied his expertise in Erlang development and testing to enhance the robustness of the build system, demonstrating careful attention to detail and a strong understanding of type systems.