def temporal_activity_score(candidate: dict, query_time: datetime) -> float:
    """
    Returns 1.0 if the entity is active at query_time, 0.1 if inactive.
    Entities without a valid_to are assumed ongoing.
    """
    valid_from = candidate.get("valid_from")
    valid_to = candidate.get("valid_to")

    if valid_to is not None:
        active = valid_from <= query_time <= valid_to
    else:
        active = valid_from <= query_time if valid_from else True

    return 1.0 if active else 0.1