问题: _custom_publish / _proto_publish / _sim_publish 只 catch json.JSONDecodeError, MqttClient.publish() 抛出的 ConnectionError 等异常未被捕获, 在 Qt 信号槽中导致静默崩溃(Windows 无 traceback). 修复: - _custom_publish: +except Exception, 避免 toPlainText() 重复调用 - _proto_publish: +except Exception, 避免 toPlainText() 重复调用 - _sim_publish: +except Exception - _custom_subscribe/_custom_unsubscribe: +except Exception, +_client 空检查