StepSecurity Harden Runner: Detect source code tampering during the build process

StepSecurity's Harden Runner is a GitHub Actions agent that detects unauthorized source code tampering during the build process, addressing the type of supply chain attack seen in the 2020 SolarWinds breach. It uses the Linux audit framework to monitor file modifications on GitHub-hosted runners and surfaces detections as error annotations in the workflow, including the syscall and executable responsible. The tool is already used in 500+ repositories including projects from Google, Microsoft, and Automattic, and is available on the GitHub Actions marketplace.