Kirill Zhumarin focused on stabilizing and maintaining complex systems across two open-source projects. In TanStack/virtual, he addressed a critical bug in multi-lane masonry rendering by refining the range calculation logic, ensuring that visible items aligned correctly with their respective lanes and preventing rendering inconsistencies. His work involved deep understanding of component and UI development using TypeScript and JavaScript. In manticoresoftware/manticoresearch, Kirill improved build reliability by resolving GCC 14 compatibility issues, updating build configurations, and documenting the rationale for future maintainability. His contributions reflect a strong emphasis on code stability, cross-toolchain compatibility, and robust engineering practices in C++ environments.