Maciej Lesniewski enhanced the Expensify/App and callstack-internal/Expensify-App repositories by delivering two core features focused on navigation and telemetry. He modernized the navigation system using React and Webpack, introducing AppNavigator with prefetching, advanced code-splitting, and lazy loading to improve performance and maintainability. For the Reports tab, he refined telemetry instrumentation in JavaScript and TypeScript, adding render time metrics and optimizing span management for more reliable workflow monitoring. His work addressed both user experience and codebase reliability, demonstrating depth in frontend development and navigation logic while ensuring the changes were robust, maintainable, and aligned with project requirements.