Worked on backend reliability within the sveltejs/kit repository, focusing on error handling during fetch requests. Addressed a critical issue where existing headers were being discarded when setting the x-sveltekit-error header in error-state fetches, which previously led to failures when interacting with external services on error pages. The solution preserved all sub-request headers, ensuring seamless integration and improved reliability for downstream services. Validated the fix with targeted checks to maintain consistency with existing fetch semantics and minimize risk. Utilized JavaScript and full stack development skills to enhance error user experience and align with broader performance and reliability objectives.