Worked on enhancing the PowerShell shell selection logic for the gitlabhq/gitlab-runner repository, focusing on improving the reliability of CI executions across different operating systems. Developed a feature in Go that ensures the correct default shell is selected based on both OS and shell type, addressing previous issues with random or incorrect shell assignment. Added comprehensive test coverage to validate the new selection behavior, which helps prevent regressions and reduces misconfigurations in pipelines. The approach emphasized backend development and robust testing practices, resulting in more deterministic runner behavior and minimizing runtime errors caused by shell misidentification during automated builds.