During December 2025, Felix Haehnel focused on backend development for the getsentry/sentry-cli repository, addressing a critical issue in the sourcemap injection workflow. He fixed a bug where .map files were incorrectly treated as JavaScript, which risked corrupting sourcemaps essential for debugging. Using Rust, Felix refactored the file discovery and injection logic to clearly separate JavaScript and sourcemap handling, ensuring only valid files were injected. He also introduced regression tests to guarantee .map files remain unaltered in future updates. This work improved the reliability of sourcemap processing in CI/CD environments, demonstrating depth in Rust and backend engineering practices.