Marcin Gosz developed a robust caching layer for newsletter subscriptions in the guardian/dotcom-rendering repository, focusing on reducing backend load and improving performance for signed-out users. He implemented precise cache invalidation logic to ensure that data remained fresh, clearing the cache on user sign-out and when rendering pages for unsigned users. The solution was built using React and leveraged advanced state management techniques in both JavaScript and TypeScript. Marcin also expanded the test suite to validate caching behavior and refresh flows, ensuring reliability and maintainability. This work addressed performance bottlenecks and enhanced the user experience for unauthenticated visitors.