Function project_root 

pub fn project_root() -> &'static Path

The project root of the run, discovered once from the working directory.

This is the single answer to “which directory does a leading / in a link name”. MD051 resolves repository-absolute link targets against it and MD057 validates absolute destinations against it, so both rules have to be looking at the same directory or one would report a link the other resolves.

Discovery is a filesystem walk and the working directory does not change during a run, so it is done once. A rule handed an explicit base (MD057’s configured roots, a test’s with_path) uses that instead.