Lewis Thorley enhanced reliability and determinism in the Netlify Build and CLI repositories by focusing on error handling, dependency management, and build process consistency. He improved HTTP error handling in netlify/build by updating error snapshots to use structured JSON payloads, ensuring clearer error reporting and easier debugging. Lewis also streamlined the build process by making manifest and metadata generation unconditional, removing feature flags to guarantee consistent outputs. In netlify/cli, he upgraded the blob dependency to incorporate recent fixes and performance improvements. His work leveraged JavaScript, TypeScript, and Node.js, demonstrating a strong grasp of build systems and robust software engineering practices.