tets

        sent_total += chunk;

    }

    // FIN-only: send an empty STREAM frame with FIN when there's no data

    // (e.g. sendStreamData(sid, nullptr, 0, true) after prior data sends).

    // The main loop doesn't execute when send_len == 0, so handle it here.

    if (send_len == 0 && fin && !stream.send_fin) {

        // Build STREAM frame: type=0x09 (FIN + no LEN), OFF bit if offset > 0

        std::vector<uint8_t> stream_frame;

        uint8_t frame_type = 0x08 | 0x01; // FIN bit

        if (stream.send_offset > 0) frame_type |= 0x04; // OFF bit

        stream_frame.push_back(frame_type);

        uint8_t vbuf[8];

        size_t vlen = encodeVarInt(stream_id, vbuf);

        stream_frame.insert(stream_frame.end(), vbuf, vbuf + vlen);

        if (stream.send_offset > 0) {

            vlen = encodeVarInt(stream.send_offset, vbuf);

            stream_frame.insert(stream_frame.end(), vbuf, vbuf + vlen);

        }

        // No data, no LEN — just the FIN flag

        uint64_t pn_before = _app_pn_send;

        std::vector<uint8_t> packet = buildShortHeaderPacket(stream_frame);

        const uint8_t* hp_key = _is_server ? _app_hp_server : _app_hp_client;

        applyHeaderProtection(packet, hp_key);

        sendPacket(packet.data(), packet.size());

        recordSentPacket(pn_before, stream_id, stream.send_offset, nullptr, 0, true);

        stream.send_fin = true;

    }

    return sent_total;

}