Worked on modernizing the build system for the RobotLocomotion/drake repository by transitioning all debug builds from the Mold linker to LLVM lld as the default, streamlining the toolchain and reducing external dependencies. This change involved updating Bazel build configurations, removing Mold-specific flags and package requirements, and ensuring continued flexibility by allowing developers to opt in to Mold via command-line options. The approach improved consistency across development and CI environments while simplifying onboarding. The work required expertise in Bazel, linker configuration, and Linux build engineering, and included targeted fixes to prevent regressions during the transition from Mold to lld.