Worked on the withastro/starlight repository to address a regression affecting the global Table of Contents configuration, focusing on stability and correctness in documentation navigation. Delivered a targeted fix that ensured user-defined heading visibility settings were consistently respected, integrating zod v4 validation to align configuration with expected behavior. This solution improved the reliability of TOC rendering across documentation pages, reducing navigation inconsistencies and support overhead. The work involved close collaboration on the patch and emphasized traceability through a single, well-documented commit. Utilized TypeScript for front end development and testing, demonstrating attention to code quality and configuration-driven user experience.