Function stable_id 

pub fn stable_id(source: &ModelSource) -> String

The stable identity of a model: the first eight bytes of the SHA-256 of the source’s (kind, path, repo) fields, hex-encoded. The fields are hashed with a length prefix so the mapping is injective — a | (or any byte) inside a path or repo cannot make two distinct sources collide. Two sources with the same kind, path, and repo map to the same id.