def check_counts(previous: dict[str, int] | None, current: dict[str, int], max_drop: float = 0.10) -> list[str]:
    """Configs whose row count dropped more than max_drop. Configs absent on either side are skipped."""
    if not previous:
        return []
    return [
        f"{cfg}: {prev} -> {current[cfg]}"
        for cfg, prev in previous.items()
        if cfg in current and prev and current[cfg] < prev * (1 - max_drop)
    ]