...time("%Y-%m-%d %H:%M:%S")
    except Exception:
        return "UNKNOWN"

def export_conversation(conv: dict, index: int):
    messages = extract_messages(conv)
    if not messages:
        return  # nichts zu exportieren

    title = sanitize_title(conv.get("title", ""))
    conv_id = conv.get("id", "")
    start_ts = conv.get("create_time") or (messages[0][0] if messages else 0)
    start_time_str = f...