Mikkel Hansen focused on backend development and testing for the medusajs/medusa repository, where he delivered a targeted bug fix to the promotion module. He addressed a correctness issue in the Promotion Rules IN operator, ensuring it now evaluates as IN rather than EQUALS, which aligns with business logic for category and tag matching. Using TypeScript and leveraging his API development skills, Mikkel also implemented integration tests to validate the fix and prevent future regressions. This work improved the reliability of promotion evaluations, reducing misapplied discounts and potential revenue leakage, and demonstrated careful attention to both code quality and business requirements.