Worked on stabilizing chat user experience in the langchain4j/langchain4j repository by implementing a memory-layer enhancement that ensures the system message consistently resides at index zero within both MessageWindowChatMemory and TokenWindowChatMemory. This approach addressed deterministic system prompt handling, resulting in more predictable chat sessions and improved cross-module consistency. The solution was developed in Java, with a strong emphasis on software design and comprehensive unit testing to validate both positive and negative scenarios. API compatibility was maintained throughout, minimizing user impact while laying groundwork for future improvements in memory management and prompt handling across the product’s chat infrastructure.