Worked on the m1a2st/kafka repository to address stability issues in Kafka’s in-sync replica (ISR) management during partition reassignments. Focused on backend development using Java, the developer implemented a targeted bug fix that allows reassignment completion even if some target replicas are temporarily outside the ISR, provided the overall ISR size is maintained. This approach reduces the risk of stalled rebalances caused by unhealthy replicas, improving cluster availability and maintenance reliability. The solution was thoroughly tested and reviewed in collaboration with other contributors, emphasizing safe ISR handling and robust backend logic to ensure system stability during maintenance windows.