Index: lib/Comms/include/MqttClient.h
===================================================================
diff -u -r51e99f2578e0901d9da91a4cb60d1b8858cfe971 -raaebfee335c74b0250864a6dce0555f866adadea
--- lib/Comms/include/MqttClient.h	(.../MqttClient.h)	(revision 51e99f2578e0901d9da91a4cb60d1b8858cfe971)
+++ lib/Comms/include/MqttClient.h	(.../MqttClient.h)	(revision aaebfee335c74b0250864a6dce0555f866adadea)
@@ -17,25 +17,14 @@
 #include <QObject>
 #include <QSslConfiguration>
 #include <QString>
+#include <QtMqtt/QMqttClient>
+#include <QtMqtt/QMqttMessageStatusProperties>
 
 class QMqttClient;
 
 /*!
- * \brief   Publishes messages to the cloud over MQTT.
- * \details Wraps QtMqtt's QMqttClient for a QoS 1 publishing session.
- *
- *          The lifecycle is init() -> open() -> close(). init() only validates
- *          the configuration and builds the TLS configuration from it; the
- *          QMqttClient itself is created by open() and destroyed by close(),
- *          or by an unsolicited disconnect. A close()/open() pair is therefore
- *          a full reset, which is what allows the session to be reopened with
- *          rotated credentials.
- * \note    Connecting is asynchronous: open() only starts the attempt, and a
- *          true return does not mean the broker accepted the session.
- * \note    Must live on the thread that calls open(): the client's socket
- *          belongs to the thread that constructs it.
- * \note    The connection is always TLS. init() fails unless keyPath names a
- *          readable private key.
+ * \brief   Encrypted client MQTT connection to a broker for message sending and receiving.
+ *          Lifecycle: init() -> open() -> close().
  */
 class MqttClient : public QObject
 {
@@ -62,19 +51,37 @@
     ~MqttClient() override;
 
     bool init(const Config &config);
-
-public Q_SLOTS:
     bool open();
     void close();
-    bool publish(const QString &topic, const QByteArray &payload, qint64 messageId = -1);
+    bool publish(const QString &topic, const QByteArray &payload, qint32 &msgId, quint8 qos=1);
+    bool subscribe(const QString &topicFilter, quint8 qos=1);
 
-private:
+Q_SIGNALS:
+    /*!
+     * \brief   Emitted when the state of the session changes (i.e. connect, disconnect)
+     * \note    Subscriptions belong to the QMqttClient that gets destroyed on disconnect,
+     *          so re-subscription is required on every new connection.
+     * \note    Not emitted for a caller-initiated close()
+     */
+    void didStateChanged(QMqttClient::ClientState state);
+
+    /*!
+     * \brief   Emitted for status change of every sent message.
+     */
+    void didMessageStatusChanged(quint32 id, QMqtt::MessageStatus status,
+        const QMqttMessageStatusProperties &properties);
+
+    /*!
+     * \brief   Emitted for every message the broker delivers to this client.
+     * \details Covers all active subscriptions; the receiver demultiplexes by topic.
+     */
+    void didMessageReceived(const QString &topic, const QByteArray &payload);
+
+private Q_SLOTS:
     void onStateChanged();
-    void onMessageSent(qint32 id);
-    void failPending();
 
+private:
     QMqttClient *_client = nullptr;
     Config _config;
     QSslConfiguration _sslConfig;
-    QHash<qint32, qint64> _pending;
 };