fix(mqtt): raise QoS1 retransmit timeout to stop duplicate /status storms

esp-mqtt's default message_retransmit_timeout is 1000 ms: any unacked QoS 1 PUBLISH is resent (byte-identical, DUP=1) every second until the PUBACK arrives or the outbox entry expires (30 s). Status messages are the only QoS 1 publishes; on a congested or recovering uplink where broker acks take several seconds, each 5-minute /status was delivered ~6 times, ~1 s apart, as exact copies (same timestamp and stats). Downstream observers flagged excessive_packet_copies and at least one broker treats it as abuse.

Expose message_retransmit_timeout via PsychicMqttClient and set it to 15 s in optimizeMqttClientConfig: one retry still fits inside the 30 s outbox expiry, preserving at-least-once delivery while capping duplicates at one.

/packets paths are QoS 0 and were never affected.

Author: agessaman

lib/PsychicMqttClient/src/PsychicMqttClient.cpp

@@ -59,6 +59,17 @@ PsychicMqttClient &PsychicMqttClient::setAutoReconnect(bool reconnect)
     return *this;
 }
 
+PsychicMqttClient &PsychicMqttClient::setMessageRetransmitTimeout(int timeoutMs)
+{
+#if ESP_IDF_VERSION_MAJOR == 5
+    _mqtt_cfg.session.message_retransmit_timeout = timeoutMs;
+#else
+    _mqtt_cfg.message_retransmit_timeout = timeoutMs;
+#endif
+    _config_dirty = true;
+    return *this;
+}
+
 PsychicMqttClient &PsychicMqttClient::setClientId(const char *clientId)
 {
 #if ESP_IDF_VERSION_MAJOR == 5

lib/PsychicMqttClient/src/PsychicMqttClient.h

@@ -126,6 +126,17 @@ class PsychicMqttClient
      */
     PsychicMqttClient &setAutoReconnect(bool reconnect = true);
 
+    /**
+     * @brief Sets the retransmit timeout for unacknowledged QoS 1/2 messages.
+     * esp-mqtt resends an unacked PUBLISH (DUP flag set) every time this
+     * timeout elapses, so a value shorter than the broker's ack latency
+     * produces byte-identical duplicates on the wire.
+     *
+     * @param timeoutMs Retransmit timeout in milliseconds. esp-mqtt's default is 1000.
+     * @return A reference to the PsychicMqttClient instance.
+     */
+    PsychicMqttClient &setMessageRetransmitTimeout(int timeoutMs);
+
     /**
      * @brief Sets the client ID for the MQTT connection.
      *

src/helpers/bridges/MQTTBridge.cpp

@@ -3323,6 +3323,15 @@ void MQTTBridge::optimizeMqttClientConfig(PsychicMqttClient* client, bool needs_
   client->setKeepAlive(75);
 #endif
 
+  // QoS 1 retransmit timeout for unacked PUBLISHes (status messages). esp-mqtt's
+  // 1000 ms default resends a byte-identical duplicate every second whenever the
+  // broker's PUBACK takes >1s — on a congested or recovering uplink this floods
+  // subscribers with exact copies of one /status message (observed 6 copies ~1s
+  // apart after an ISP outage; brokers may drop the session as spam). 15s allows
+  // one retry before the outbox entry expires (esp-mqtt outbox expiry is 30s),
+  // preserving at-least-once delivery while capping duplicates at one.
+  client->setMessageRetransmitTimeout(15000);
+
   // Buffer sizing: 896 is the minimum safe size for JWT clients (CONNECT + 768-byte JWT).
   // On PSRAM boards, use a uniform size to reduce fragmentation from mixed allocations.
   // On non-PSRAM boards, use smaller buffers for non-JWT slots to reduce heap usage and