In December 2024, Kapust developed the UI Thread Lock Contention Warning System for the facebook/infer repository, targeting performance issues caused by synchronous locks on the UI thread. Using Java and leveraging concurrency and performance optimization skills, Kapust designed the system to detect and warn when UI thread contention could degrade responsiveness. The implementation included comprehensive documentation and automated tests to ensure reliability and clarity for other developers. By enhancing observability into contention hotspots, this work enabled faster diagnosis and remediation of UI stalls. The feature demonstrated depth in concurrency instrumentation and contributed to more robust, maintainable code within the Infer project.