Function relative_key_path 

pub fn relative_key_path(path: &Path, root: &Path) -> String

Canonical path form used inside audit attribution keys: root-relative with forward slashes on every platform. Paths outside root keep their simplified absolute form so keys stay unique.

The engine keys its per-module maps with this function, and fallow-api builds its lookup keys with the same function, so both sides of the join always agree.