Merge fix/improve-error-logging: Human-readable MQTT errors

- Add TLS security warning when certificate verification is disabled
- Add getMQTTErrorString() to translate PubSubClient error codes
- Show broker/user info on connection failure for debugging
- Standardize log prefix to [MQTT] (was inconsistent [MQTTS])
- Use transport-agnostic "Network" instead of "WiFi" in messages
- Fix WiFiState/NetworkState enum mismatch in getWiFiStatus()

Error codes now show meaningful messages like:
  "Bad credentials (check username/password)" instead of "rc=4"

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),
@@ -45,10 +46,11 @@ void MQTTBridge::begin(const MQTTConfig& config, const uint8_t* self_pubkey) {
   if (_config.use_tls) {
     _wifi_client_secure.setInsecure();  // Skip cert verification
     _mqtt_client.setClient(_wifi_client_secure);
-    Serial.printf("[MQTT] TLS enabled\n");
+    Serial.println("[MQTT] TLS enabled");
+    Serial.println("[MQTT] WARNING: Certificate verification DISABLED - vulnerable to MITM attacks!");
   } else {
     _mqtt_client.setClient(_wifi_client);
-    Serial.printf("[MQTT] Plain TCP\n");
+    Serial.println("[MQTT] Plain TCP (no encryption)");
   }
 
   _mqtt_client.setServer(_config.broker, _config.port);
@@ -73,14 +75,15 @@ void MQTTBridge::loop() {
   if (!_network->isConnected()) {
     if (_state == MQTTState::CONNECTED) {
       _state = MQTTState::DISCONNECTED;
-      Serial.println("[MQTTS] WiFi lost, disconnected");
+      Serial.println("[MQTT] Network connection lost, disconnecting");
     }
     return;
   }
 
   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;
@@ -91,8 +94,9 @@ void MQTTBridge::loop() {
     case MQTTState::CONNECTED:
       if (!_mqtt_client.connected()) {
         _state = MQTTState::DISCONNECTED;
-        Serial.println("[MQTTS] Connection lost");
+        Serial.println("[MQTT] Connection lost");
         _last_connect_attempt = millis();
+        // Don't reset backoff on connection loss - broker might be down
       } else {
         _mqtt_client.loop();
 
@@ -104,7 +108,8 @@ 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;
@@ -125,7 +130,7 @@ void MQTTBridge::end() {
 
   _state = MQTTState::DISCONNECTED;
   _initialized = false;
-  Serial.println("[MQTTS] Stopped");
+  Serial.println("[MQTT] Stopped");
 }
 
 void MQTTBridge::attemptConnection() {
@@ -134,7 +139,8 @@ void MQTTBridge::attemptConnection() {
   _state = MQTTState::CONNECTING;
   _last_connect_attempt = millis();
 
-  Serial.printf("[MQTTS] Connecting to %s:%d...\n", _config.broker, _config.port);
+  Serial.printf("[MQTT] 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) {
@@ -157,15 +163,41 @@ void MQTTBridge::attemptConnection() {
     _state = MQTTState::CONNECTED;
     _connected_since = millis();
     _reconnect_count++;
-    Serial.println("[MQTTS] Connected!");
+    // Reset backoff on successful connection
+    _current_backoff_ms = BACKOFF_MIN_MS;
+    Serial.println("[MQTT] Connected!");
 
     subscribeToCommands();
     publishStatus();
     _last_status_publish = millis();
   } else {
     int rc = _mqtt_client.state();
-    Serial.printf("[MQTTS] Connection failed, rc=%d\n", rc);
+    const char* error_str = getMQTTErrorString(rc);
+    Serial.printf("[MQTT] Connection failed: %s (code %d)\n", error_str, rc);
+    Serial.printf("[MQTT] Broker: %s:%d, User: %s\n", _config.broker, _config.port,
+                  strlen(_config.user) > 0 ? _config.user : "(none)");
     _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);
+  }
+}
+
+const char* MQTTBridge::getMQTTErrorString(int rc) {
+  // PubSubClient state() return codes
+  switch (rc) {
+    case -4: return "Connection timeout";
+    case -3: return "Connection lost";
+    case -2: return "Connect failed (network)";
+    case -1: return "Disconnected cleanly";
+    case 0:  return "Connected";
+    case 1:  return "Bad protocol version";
+    case 2:  return "Client ID rejected";
+    case 3:  return "Server unavailable";
+    case 4:  return "Bad credentials (check username/password)";
+    case 5:  return "Not authorized";
+    default: return "Unknown error";
   }
 }
 
@@ -188,7 +220,7 @@ void MQTTBridge::subscribeToCommands() {
   char topic[100];
   snprintf(topic, sizeof(topic), "%s#", _topic_cmd_prefix);
   _mqtt_client.subscribe(topic);
-  Serial.printf("[MQTTS] Subscribed to: %s\n", topic);
+  Serial.printf("[MQTT] Subscribed to: %s\n", topic);
 }
 
 void MQTTBridge::updateConfig(const MQTTConfig& config) {
@@ -333,7 +365,7 @@ void MQTTBridge::publishMessage(const char* topic, const char* payload, bool ret
   if (_mqtt_client.publish(topic, payload, retained)) {
     _messages_sent++;
   } else {
-    Serial.printf("[MQTTS] Publish failed to %s\n", topic);
+    Serial.printf("[MQTT] Publish failed to %s\n", topic);
   }
 }
 
@@ -380,10 +412,10 @@ void MQTTBridge::handleMessage(char* topic, uint8_t* payload, unsigned int lengt
 
   if (strncmp(topic, _topic_cmd_prefix, strlen(_topic_cmd_prefix)) == 0) {
     const char* cmd = topic + strlen(_topic_cmd_prefix);
-    Serial.printf("[MQTTS] Command received: %s\n", cmd);
+    Serial.printf("[MQTT] Command received: %s\n", cmd);
 
     if (strcmp(cmd, "reboot") == 0) {
-      Serial.println("[MQTTS] Reboot requested");
+      Serial.println("[MQTT] Reboot requested");
       publishStatus();
       delay(100);
       ESP.restart();

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;
@@ -111,6 +117,9 @@ private:
   void publishMessage(const char* topic, const char* payload, bool retained = false);
   void publishJson(const char* topic, JsonDocument& doc, bool retained = false);
 
+  // Error code translation for better diagnostics
+  static const char* getMQTTErrorString(int rc);
+
   static uint32_t fnv1a_hash(const uint8_t* data, size_t len);
   bool isDuplicate(const uint8_t* data, size_t len);
 

src/WiFiManager.cpp

@@ -10,6 +10,7 @@ WiFiManager::WiFiManager()
       _retry_count(0),
       _initialized(false) {
   memset(&_config, 0, sizeof(_config));
+  memset(_cached_ssid, 0, sizeof(_cached_ssid));
 }
 
 void WiFiManager::begin(const WiFiConfig& config) {
@@ -82,6 +83,9 @@ void WiFiManager::loop() {
         _state = WiFiState::CONNECTED;
         _connected_since = millis();
         _retry_count = 0;
+        // Cache SSID to avoid dangling pointer from WiFi.SSID().c_str()
+        strncpy(_cached_ssid, WiFi.SSID().c_str(), sizeof(_cached_ssid) - 1);
+        _cached_ssid[sizeof(_cached_ssid) - 1] = '\0';
         Serial.printf("[WiFi] Connected! IP: %s, RSSI: %d dBm\n",
                       WiFi.localIP().toString().c_str(), WiFi.RSSI());
       } else if (status == WL_NO_SSID_AVAIL) {
@@ -184,6 +188,9 @@ void WiFiManager::startAPMode() {
 
   if (success) {
     _state = WiFiState::AP_MODE;
+    // Cache AP SSID to avoid dangling pointer
+    strncpy(_cached_ssid, ap_ssid.c_str(), sizeof(_cached_ssid) - 1);
+    _cached_ssid[sizeof(_cached_ssid) - 1] = '\0';
     Serial.printf("[WiFi] AP started: SSID='%s', IP=%s\n",
                   ap_ssid.c_str(), WiFi.softAPIP().toString().c_str());
   } else {
@@ -221,10 +228,8 @@ int32_t WiFiManager::getRSSI() const {
 }
 
 const char* WiFiManager::getSSID() const {
-  if (_state == WiFiState::CONNECTED) {
+  if (_state == WiFiState::CONNECTED || _state == WiFiState::AP_MODE) {
-    return WiFi.SSID().c_str();
+    return _cached_ssid;
-  } else if (_state == WiFiState::AP_MODE) {
-    return WiFi.softAPSSID().c_str();
   }
   return "";
 }
@@ -264,10 +269,8 @@ NetworkState WiFiManager::getState() const {
 }
 
 const char* WiFiManager::getConnectionName() const {
-  if (_state == WiFiState::CONNECTED) {
+  if (_state == WiFiState::CONNECTED || _state == WiFiState::AP_MODE) {
-    return WiFi.SSID().c_str();
+    return _cached_ssid;
-  } else if (_state == WiFiState::AP_MODE) {
-    return WiFi.softAPSSID().c_str();
   }
   return "Not connected";
 }

src/WiFiManager.h

@@ -61,6 +61,7 @@ private:
   unsigned long _connected_since;
   uint8_t _retry_count;
   bool _initialized;
+  char _cached_ssid[33];  // Cached SSID to avoid dangling pointer from WiFi.SSID().c_str()
 
   void attemptConnection();
   void checkConnection();