Worked on the bazelbuild/rules_rust repository to address a critical issue in the cargo_build_script_runner, focusing on the correctness and downstream compatibility of Cargo metadata propagation. Delivered a targeted bug fix that ensures cargo::metadata key/value pairs are emitted as Cargo-compatible DEP_* environment variables, replacing legacy formats and improving integration for dependent crates. Enhanced the metadata parser to correctly route and handle both valid and malformed metadata payloads, preserving build reproducibility. Developed and expanded unit and end-to-end integration tests using Rust and Bazel, validating the solution’s effectiveness and improving CI reliability. Demonstrated skills in build systems, Rust, and testing methodologies.