def extract_sample_id(metadata):
    """
    Best-effort extraction of a sample identifier from the metadata stored in
    dataset info entries or collate_fn outputs.
    """
    if metadata is None:
        return None

    if isinstance(metadata, dict):
        sample_id = metadata.get("id") or metadata.get("sample_id")
        if sample_id is not None:
            return str(sample_id)

    if isinstance(metadata, (list, tuple)):
        for item in metadata:
            sample_id = extract_sample_id(item)
            if sample_id:
                return sample_id
        return None

    if isinstance(metadata, (int, float)):
        # treat bare numeric IDs as strings to keep files consistent
        return str(int(metadata))

    if isinstance(metadata, str):
        return metadata.strip()

    return None