Function run_cascade 

pub fn run_cascade(
    specs: &[EditSpec],
    files: &mut [FileBuf],
) -> Result<Vec<EditOutcome>, String>

Run the script with cascade: edits run in script order, each matching the buffers as already transformed by earlier edits, exactly as the final write would have it. Buffers are updated even past a failing edit so the remaining diagnostics stay meaningful; the caller writes nothing unless every outcome is SUCCESS.