Worked on the mastra-ai/mastra repository to enhance type safety and maintainability within the authentication subsystem using TypeScript. Focused on resolving a type compatibility issue in CompositeAuth, enabling the seamless combination of typed authentication providers with narrower TUser types under strict mode. Addressed this by converting property declarations to method shorthand, which allowed for bivariant parameter checking without introducing runtime changes. Added a type-level regression test to validate the fix and scoped changes to mapUserToResourceId declarations. The work improved developer experience for integrating multiple authentication strategies and strengthened platform stability, leveraging skills in software development and TypeScript.