Worked on the nestjs/nest repository to enhance reliability in microservice messaging, focusing on MQTT and Kafka integration using TypeScript. Developed features enabling per-handler Quality of Service settings for MQTT subscriptions, allowing different delivery guarantees for individual message handlers and increasing operational flexibility. Added comprehensive test coverage to verify that Kafka run options are correctly forwarded to consumer.run(), strengthening integration reliability and reducing configuration drift. Emphasized maintainability and stability by combining feature development with robust testing practices. Leveraged expertise in Kafka, MQTT, and microservices to deliver targeted improvements that support ongoing maintenance and operational confidence without introducing new bugs during the period.