Function lfs_object_key 

pub fn lfs_object_key(oid: &str) -> String

Cache key of an LFS object: its path relative to the cache root, /-joined so it matches the keys the eviction index uses for mirrors. Content-addressed and shared across all repos (the oid is the content hash), sharded by the first two hex chars so no single directory holds every object. Caller must pass a valid_lfs_oid.