wtf is libraries-repository-engine?

Arduino's Library Manager is how people find and install add-on code for their Arduino projects. The libraries-repository-engine is the tool behind the scenes that keeps that catalog fresh, it figures out which libraries have new versions available and adds them to the index that the Arduino software checks when you browse for libraries. The tool runs automatically every hour. It goes through a list of library repositories that Arduino has approved, checks each one for new version tags (a way developers mark a specific release), and verifies that those versions meet certain requirements. If everything checks out, the tool adds an entry for that version to the index and pushes the updated file to Arduino's download server. If a tag doesn't meet the requirements, the tool leaves it out and publishes logs explaining what happened, so library authors can see why their release wasn't included. This tool is mainly for Arduino's own infrastructure, it powers the automated indexer that runs hourly. Library authors wouldn't run it themselves, but they benefit from it indirectly: when they tag a new release of their library, this system is what eventually makes that version show up in the Library Manager for users to install. The requirements it enforces help maintain quality, for example, a new release needs to follow proper versioning and structure to make it into the index. The project is written in Go and built using a task runner called task, which handles building and testing. The README doesn't go into much detail about configuration beyond mentioning that you need a config.json and repos.txt file, and that you can run ./libraries-repository-engine help to see available commands. There's also a security policy in place for reporting vulnerabilities, which is standard for infrastructure tools like this.