Worked on the NixOS/nix repository to enhance the reliability of the build environment by addressing a critical issue in sandbox and output path handling. Focused on system programming and build systems using C++, the developer implemented a fix that reorders build steps to ensure sandbox paths are established before output paths are erased. This change resolved a bug where output paths were incorrectly removed from sandbox paths during builds, thereby improving build determinism and reproducibility. The work centered on internal hardening rather than feature development, directly contributing to more robust and isolated build pipelines for consistent and reliable software builds.