Mathieu Olivari developed and refined build system tooling across the bazelbuild/rules_swift and bazelbuild/rules_apple repositories, focusing on platform and toolchain configuration using Python and Starlark. He introduced an environment-variable-driven override for Xcode Swift toolchain target triples, enabling custom toolchains and maintaining compatibility with evolving Swift rules. In parallel, he resolved a bug in SDK environment string handling by normalizing platform strings to lowercase, preventing failures in xcrun invocations when SDK versions included letters. Mathieu’s work enhanced build reliability and predictability, demonstrating technical depth in cross-repository collaboration and a strong grasp of build system internals and configuration management.