Function leaked 

pub fn leaked(
    held_out: &[(HeldOutFile, String)],
    known: &str,
    wt_root: &Path,
    start_tree: &Checkpoint,
    patch: &str,
) -> Vec<String>

Held-out literals in the attempt’s added lines that it could only have copied: not in the spec, the visible tests or the tree it started from . For a native attempt this never fires; for an external agent, which can read the state directory, it is the mechanical check.