Expose timesync error in MQTT and web UI

BACKWARD-INCOMPATIBLE: MQTT faults payload now always includes err_last/err_last_text and err_last_age (schema change).

README.md

@@ -221,6 +221,7 @@ Fixed header (little-endian):
 - `err_d` u8 (decode failures, sender-side counter)
 - `err_tx` u8 (LoRa TX failures, sender-side counter)
 - `err_last` u8 (last error code: 0=None, 1=MeterRead, 2=Decode, 3=LoraTx, 4=TimeSync)
+- MQTT faults payload also includes `err_last_text` (string) and `err_last_age` (seconds).
 
 Body:
 - `E0` u32 (absolute energy in Wh)

src/mqtt_client.cpp

@@ -10,6 +10,21 @@ static PubSubClient mqtt_client(wifi_client);
 static WifiMqttConfig g_cfg;
 static String g_client_id;
 
+static const char *fault_text(FaultType fault) {
+  switch (fault) {
+    case FaultType::MeterRead:
+      return "meter";
+    case FaultType::Decode:
+      return "decode";
+    case FaultType::LoraTx:
+      return "loratx";
+    case FaultType::TimeSync:
+      return "timesync";
+    default:
+      return "none";
+  }
+}
+
 void mqtt_init(const WifiMqttConfig &config, const char *device_id) {
   g_cfg = config;
   mqtt_client.setServer(config.mqtt_host.c_str(), config.mqtt_port);
@@ -66,10 +81,9 @@ bool mqtt_publish_faults(const char *device_id, const FaultCounters &counters, F
   doc["err_m"] = counters.meter_read_fail;
   doc["err_d"] = counters.decode_fail;
   doc["err_tx"] = counters.lora_tx_fail;
-  if (last_error != FaultType::None) {
   doc["err_last"] = static_cast<uint8_t>(last_error);
-    doc["err_last_age"] = last_error_age_sec;
-  }
+  doc["err_last_text"] = fault_text(last_error);
+  doc["err_last_age"] = last_error != FaultType::None ? last_error_age_sec : 0;
 
   String payload;
   size_t len = serializeJson(doc, payload);
@@ -138,6 +152,8 @@ bool mqtt_publish_discovery(const char *device_id) {
   ok = ok && publish_discovery_sensor(device_id, "err_m", "Meter Read Errors", "count", "", faults_topic.c_str(), "{{ value_json.err_m }}");
   ok = ok && publish_discovery_sensor(device_id, "err_d", "Decode Errors", "count", "", faults_topic.c_str(), "{{ value_json.err_d }}");
   ok = ok && publish_discovery_sensor(device_id, "err_tx", "LoRa TX Errors", "count", "", faults_topic.c_str(), "{{ value_json.err_tx }}");
+  ok = ok && publish_discovery_sensor(device_id, "err_last", "Last Error Code", "", "", faults_topic.c_str(), "{{ value_json.err_last }}");
+  ok = ok && publish_discovery_sensor(device_id, "err_last_text", "Last Error", "", "", faults_topic.c_str(), "{{ value_json.err_last_text }}");
   ok = ok && publish_discovery_sensor(device_id, "err_last_age", "Last Error Age", "s", "", faults_topic.c_str(), "{{ value_json.err_last_age }}");
   return ok;
 }

src/web_server.cpp

@@ -59,6 +59,21 @@ static bool auth_required() {
   return g_is_ap ? WEB_AUTH_REQUIRE_AP : WEB_AUTH_REQUIRE_STA;
 }
 
+static const char *fault_text(FaultType fault) {
+  switch (fault) {
+    case FaultType::MeterRead:
+      return "meter";
+    case FaultType::Decode:
+      return "decode";
+    case FaultType::LoraTx:
+      return "loratx";
+    case FaultType::TimeSync:
+      return "timesync";
+    default:
+      return "none";
+  }
+}
+
 static bool ensure_auth() {
   if (!auth_required()) {
     return true;
@@ -97,6 +112,7 @@ static String format_faults(uint8_t idx) {
   s += String(g_sender_faults[idx].lora_tx_fail);
   s += " last:";
   s += String(static_cast<uint8_t>(g_sender_last_errors[idx]));
+  s += " (" + String(fault_text(g_sender_last_errors[idx])) + ")";
   return s;
 }
 
@@ -335,6 +351,7 @@ static String render_sender_block(const SenderStatus &status) {
   if (status.has_data) {
     s += " err_tx:" + String(status.last_data.err_lora_tx);
     s += " err_last:" + String(static_cast<uint8_t>(status.last_data.last_error));
+    s += " (" + String(fault_text(status.last_data.last_error)) + ")";
   }
   s += format_faults(idx);
   s += "<br>";
@@ -588,7 +605,7 @@ static void handle_sender() {
           html += "<td>" + String(d.link_rssi_dbm) + "</td>";
           html += "<td>" + String(d.link_snr_db, 1) + "</td>";
           html += "<td>" + String(d.err_lora_tx) + "</td>";
-          html += "<td>" + String(static_cast<uint8_t>(d.last_error)) + "</td>";
+          html += "<td>" + String(static_cast<uint8_t>(d.last_error)) + " (" + String(fault_text(d.last_error)) + ")</td>";
           html += "</tr>";
         }
         html += "</table>";