During March 2026, Berselius developed mixed compiler toolchain support for cached CMake builds in the spack/spack-packages repository. This work focused on improving build correctness and reproducibility by ensuring that compiler flags are applied only after validating the actual CXX compiler, which prevents misconfiguration of HIP and CUDA-related flags when using mixed toolchains. Berselius implemented this logic using Python scripting and CMake, addressing issues that previously led to downstream build failures in projects such as umpire. The solution demonstrates a solid understanding of build system development, with careful attention to the nuances of compiler flag management in complex toolchain environments.