Function find_ignored_paths 

pub fn find_ignored_paths(
    repo_root: &Path,
    rel_paths: &[String],
) -> FxHashSet<String>

Returns the subset of rel_paths (repo-root-relative) excluded by either .gitignore (via git’s own engine, so nesting/negation/** are handled correctly) or .diffctx/ignore (patterns anchored per-directory and fed to git as a temporary core.excludesFile, so the same engine evaluates both mechanisms uniformly). Best-effort: any failure returns an empty set rather than blocking the diff pipeline on an ignore-resolution problem.