Worked on strengthening the core dependency injection system in the nestjs/nest repository by addressing a subtle edge case in the ModuleRef class. Focused on ensuring that transient-scoped dependencies are instantiated correctly, the work involved fixing the underlying logic in ModuleRef.create and developing a comprehensive test suite to validate behavior across multiple dependency injection scenarios. This approach improved the reliability of NestJS’s DI mechanism, reducing the likelihood of runtime issues for users. The changes were implemented using TypeScript and leveraged skills in NestJS, dependency injection, and testing, contributing to greater stability and maintainability in the framework’s core infrastructure.