fix: MqttClient 重构为 QObject — publish 通过 Qt 信号排队避免 C 层崩溃

问题: paho-mqtt publish() C 扩展在 Windows 上从 GUI 线程调用时静默崩溃。

修复:
- MqttClient 改为 QObject 子类
- publish() 通过 Qt Signal(Qt.QueuedConnection) 排队，_do_publish()
  始终在主线程事件循环中执行 paho 调用
- 状态/消息通知改用 Qt Signal 跨线程传递
- 新增 subscribe()/unsubscribe() 公开 API，消除 main.py 直接
  访问 _client 的脆弱代码
- 移除 MainWindow 中已不再需要的中间信号 _mqtt_status/_mqtt_msg

DBNMQTTool/dbn_mqtt_tool/mqtt_client.py

@@ -1,7 +1,6 @@
 """
 MQTT 客户端封装
 """
-
 import json
 import time
 import threading
@@ -9,6 +8,7 @@ from typing import Callable, Optional
 from dataclasses import dataclass
 
 import paho.mqtt.client as mqtt
+from PySide6.QtCore import QObject, Signal, Slot, Qt
 
 from .protocol import parse_topic_dev_serial
 
@@ -23,67 +23,64 @@ class BrokerConfig:
     keepalive: int = 60
 
 
-class MqttClient:
-    """DLD960 IoT MQTT 客户端"""
+class MqttClient(QObject):
+    """DLD960 IoT MQTT 客户端 — QObject 基类确保信号线程安全"""
+
+    # 供外部监听
+    _status_notify = Signal(bool, str)   # connected, message
+    _msg_notify = Signal(str, str, object)  # topic, dev_serial, payload_dict
+
+    # 内部线程安全的 publish 队列
+    _publish_sig = Signal(str, str, int)  # topic, json_data, qos
 
     def __init__(self):
+        super().__init__()
         self._client: Optional[mqtt.Client] = None
         self._config = BrokerConfig()
         self._connected = False
         self._lock = threading.Lock()
-        self._message_callbacks: list[Callable[[str, str, dict], None]] = []
-        self._status_callbacks: list[Callable[[bool, str], None]] = []
+
+        # 信号→槽: publish 通过排队连接确保在主线程的 paho context 执行
+        self._publish_sig.connect(self._do_publish, Qt.QueuedConnection)
 
     @property
     def connected(self) -> bool:
         return self._connected
 
+    # ---- 公开回调 (兼容旧接口) ----
+
     def on_status_change(self, callback: Callable[[bool, str], None]):
-        self._status_callbacks.append(callback)
+        self._status_notify.connect(callback)
 
     def on_message(self, callback: Callable[[str, str, dict], None]):
         """回调参数: (topic, dev_serial, payload_dict)"""
-        self._message_callbacks.append(callback)
+        self._msg_notify.connect(callback)
 
-    def _notify_status(self, connected: bool, msg: str):
-        for cb in self._status_callbacks:
-            try:
-                cb(connected, msg)
-            except Exception:
-                pass
-
-    def _notify_message(self, topic: str, payload: dict):
-        dev_serial = parse_topic_dev_serial(topic) or ""
-        for cb in self._message_callbacks:
-            try:
-                cb(topic, dev_serial, payload)
-            except Exception:
-                pass
-
-    # ---- MQTT callbacks ----
+    # ---- MQTT callbacks (paho 网络线程) ----
 
     def _on_connect(self, client, userdata, flags, reason_code, properties=None):
         rc = reason_code if isinstance(reason_code, int) else reason_code.value
         if rc == 0:
             self._connected = True
-            self._notify_status(True, "已连接到 Broker")
+            self._status_notify.emit(True, "已连接到 Broker")
 
             from .protocol import TOPIC_ALL_DEVICE_UP
             client.subscribe(TOPIC_ALL_DEVICE_UP, qos=1)
         else:
             self._connected = False
-            self._notify_status(False, f"连接失败 (rc={rc})")
+            self._status_notify.emit(False, f"连接失败 (rc={rc})")
 
     def _on_disconnect(self, client, userdata, *args):
         self._connected = False
-        self._notify_status(False, "已断开连接")
+        self._status_notify.emit(False, "已断开连接")
 
     def _on_message(self, client, userdata, msg: mqtt.MQTTMessage):
         try:
             payload = json.loads(msg.payload.decode("utf-8"))
         except (json.JSONDecodeError, UnicodeDecodeError):
             payload = {"_raw": msg.payload.hex()}
-        self._notify_message(msg.topic, payload)
+        dev_serial = parse_topic_dev_serial(msg.topic) or ""
+        self._msg_notify.emit(msg.topic, dev_serial, payload)
 
     # ---- Public API ----
 
@@ -96,7 +93,6 @@ class MqttClient:
 
         client_id = self._config.client_id or f"dbn_mqtt_tool_{int(time.time())}"
 
-        # MQTT 5.0 用 CallbackAPIVersion.VERSION2
         self._client = mqtt.Client(
             client_id=client_id,
             protocol=mqtt.MQTTv311,
@@ -120,11 +116,30 @@ class MqttClient:
         self._connected = False
 
     def publish(self, topic: str, payload: dict, qos: int = 1):
-        """发送 JSON 消息到指定 topic"""
+        """线程安全的发布 — 通过 Qt 信号排队到主线程执行"""
         if not self._client or not self._connected:
             raise ConnectionError("MQTT 未连接")
         data = json.dumps(payload, ensure_ascii=False)
-        self._client.publish(topic, data, qos=qos)
+        self._publish_sig.emit(topic, data, qos)
+
+    def subscribe(self, topic: str, qos: int = 1):
+        """订阅主题"""
+        if self._client:
+            self._client.subscribe(topic, qos=qos)
+
+    def unsubscribe(self, topic: str):
+        """取消订阅"""
+        if self._client:
+            self._client.unsubscribe(topic)
+
+    @Slot(str, str, int)
+    def _do_publish(self, topic: str, data: str, qos: int):
+        """实际的 paho publish 调用 — 始终在主线程执行"""
+        if self._client and self._connected:
+            try:
+                self._client.publish(topic, data, qos=qos)
+            except Exception as e:
+                print(f"[MqttClient] publish error: {e}")
 
     def send_command(self, dev_serial: str, cmd: str, data: Optional[dict] = None, qos: int = 1) -> int:
         """向设备发送命令，返回 msg_id"""