During January 2025, Matheus Rufca focused on improving code safety in the paypal/paypal-js repository by enforcing immutability within the ProcessOptions path. He refactored the existing JavaScript and TypeScript code to avoid mutating input arguments, replacing delete statements with the spread operator to ensure data integrity. To support this change, Matheus added comprehensive unit tests that verify immutability and help prevent future regressions. He also documented the update with a changeset for downstream consumers. This targeted work addressed a specific bug, demonstrating careful attention to refactoring and testing practices while enhancing the reliability of the codebase without introducing new features.