Add exponential backoff to MQTT reconnection

Instead of fixed 5s/30s retry intervals, implement exponential backoff:
- Initial delay: 1 second
- Max delay: 60 seconds
- Doubles on each failed attempt
- Resets to minimum on successful connection

This prevents hammering a down broker while still reconnecting
quickly when the issue is transient.

Also includes fix for WiFiState/NetworkState enum mismatch in
getWiFiStatus() which was already on main.

src/MQTTBridge.cpp

@@ -17,6 +17,7 @@ MQTTBridge::MQTTBridge(INetworkManager* network, mesh::PacketManager* mgr, mesh:
       _last_status_publish(0),
       _last_stats_publish(0),
       _connected_since(0),
+      _current_backoff_ms(BACKOFF_MIN_MS),
       _messages_sent(0),
       _messages_received(0),
       _reconnect_count(0),
@@ -80,7 +81,8 @@ void MQTTBridge::loop() {
 
   switch (_state) {
     case MQTTState::DISCONNECTED:
-      if (millis() - _last_connect_attempt > 5000) {
+      // Use exponential backoff for reconnection attempts
+      if (millis() - _last_connect_attempt > _current_backoff_ms) {
         attemptConnection();
       }
       break;
@@ -93,6 +95,7 @@ void MQTTBridge::loop() {
         _state = MQTTState::DISCONNECTED;
         Serial.println("[MQTTS] Connection lost");
         _last_connect_attempt = millis();
+        // Don't reset backoff on connection loss - broker might be down
       } else {
         _mqtt_client.loop();
 
@@ -104,7 +107,8 @@ void MQTTBridge::loop() {
       break;
 
     case MQTTState::ERROR:
-      if (millis() - _last_connect_attempt > 30000) {
+      // Use backoff for error recovery too
+      if (millis() - _last_connect_attempt > _current_backoff_ms) {
         _state = MQTTState::DISCONNECTED;
       }
       break;
@@ -134,7 +138,8 @@ void MQTTBridge::attemptConnection() {
   _state = MQTTState::CONNECTING;
   _last_connect_attempt = millis();
 
-  Serial.printf("[MQTTS] Connecting to %s:%d...\n", _config.broker, _config.port);
+  Serial.printf("[MQTTS] Connecting to %s:%d (backoff=%lums)...\n",
+                _config.broker, _config.port, _current_backoff_ms);
 
   String client_id = String(_config.client_id);
   if (client_id.length() == 0) {
@@ -157,6 +162,8 @@ void MQTTBridge::attemptConnection() {
     _state = MQTTState::CONNECTED;
     _connected_since = millis();
     _reconnect_count++;
+    // Reset backoff on successful connection
+    _current_backoff_ms = BACKOFF_MIN_MS;
     Serial.println("[MQTTS] Connected!");
 
     subscribeToCommands();
@@ -166,6 +173,10 @@ void MQTTBridge::attemptConnection() {
     int rc = _mqtt_client.state();
     Serial.printf("[MQTTS] Connection failed, rc=%d\n", rc);
     _state = MQTTState::ERROR;
+
+    // Exponential backoff: double the delay (up to max)
+    _current_backoff_ms = min(_current_backoff_ms * BACKOFF_MULTIPLIER, BACKOFF_MAX_MS);
+    Serial.printf("[MQTTS] Next retry in %lums\n", _current_backoff_ms);
   }
 }
 

src/MQTTBridge.h

@@ -85,6 +85,12 @@ private:
   unsigned long _last_stats_publish;
   unsigned long _connected_since;
 
+  // Exponential backoff for reconnection
+  static constexpr uint32_t BACKOFF_MIN_MS = 1000;      // Start at 1 second
+  static constexpr uint32_t BACKOFF_MAX_MS = 60000;     // Max 60 seconds
+  static constexpr uint32_t BACKOFF_MULTIPLIER = 2;     // Double each attempt
+  uint32_t _current_backoff_ms;
+
   uint32_t _messages_sent;
   uint32_t _messages_received;
   uint32_t _reconnect_count;

src/MyMesh.cpp

@@ -1289,9 +1289,9 @@ const char* MyMesh::getMQTTStatus() const {
 
 const char* MyMesh::getWiFiStatus() const {
   switch (_wifi_mgr.getState()) {
-    case WiFiState::CONNECTED: return "connected";
-    case WiFiState::CONNECTING: return "connecting";
-    case WiFiState::AP_MODE: return "ap_mode";
+    case NetworkState::CONNECTED: return "connected";
+    case NetworkState::CONNECTING: return "connecting";
+    case NetworkState::AP_MODE: return "ap_mode";
     default: return "disconnected";
   }
 }