Function run_asset_diff 

pub fn run_asset_diff(
    before_path: &Path,
    after_path: &Path,
    kind: &ArtifactKind,
    goal_intent: &str,
    config: &AssetDiffConfig,
    staging_dir: &Path,
) -> AssetDiffResult

Run the full asset diff pipeline for a single before/after artifact pair.

The function is infallible — on any error it returns a result with skipped_reason set and all optional fields as None.