Thomas Peklak enhanced session handling in the better-auth/better-auth repository by developing a feature for the Custom Session Plugin that preserves individual Set-Cookie headers and retains Max-Age attributes when caching is enabled. He addressed the risk of header clobbering by implementing the getSetCookie() method, ensuring that cookie integrity is maintained across clients. Using TypeScript and Node, Thomas also wrote comprehensive tests to validate cookie behavior under caching scenarios, focusing on reliability and security. His work demonstrated a solid understanding of full stack development and testing, delivering a targeted solution that improved session management without introducing unnecessary complexity.