Vincent Cheng developed the Codex Phase Parameter Preservation feature for the UKGovernmentBEIS/inspect_ai repository, focusing on maintaining phase metadata during history reconstruction in the Responses API. He designed a solution in Python that preserved the 'phase' field, such as 'commentary' or 'final_answer', through internal representations to ensure alignment with GPT-5.3 Codex outputs. By leveraging API development and unit testing skills, Vincent enabled accurate pass-through of phase parameters with minimal changes to the API surface. This work improved traceability and model output fidelity, addressing performance concerns and delivering a robust, maintainable enhancement without introducing new bugs during the development period.