Function ledger_dir 

pub fn ledger_dir(cache_root: &Path, repo_path: &Path) -> PathBuf

Compute the per-repo ledger directory: <cache_root>/codelore/<repo_hash_8>/

Delegates to crate::cache::repo_cache_dir so the derivation is defined in exactly one place (shared with the cache .duckdb path and the external-findings sidecar).