Worked on the lichess-org/lila repository to deliver cross-platform rematch challenges, enabling OAuth and mobile access while ensuring cache integrity for rematch offers. Addressed issues with duplicate rematch offers by implementing centralized cache invalidation, dropping cached offer IDs on cancel or decline to maintain consistent behavior across web and mobile platforms. Refactored backend logic in Scala to extract reusable cache-management helpers, improving maintainability and reducing incident-prone edge cases. Focused on backend development, API design, and caching strategies, the work enhanced reliability and user experience for rematch flows, aligning feature parity and reducing errors related to stale state in rematch offers.