feat: publish now-playing artist/album over MQTT + Home Assistant sensors

Roadmap item 7. Publishes the ID3 artist and album to new MQTT state topics
(track_artist / track_album, next to the existing track title + cover_changed),
reset per track and re-published on (re)connect, plus Home-Assistant discovery sensors
(Artist, Album) mirroring the existing Track sensor.

Compile-verified; MQTT runtime not exercised on the test device (no broker / MQTT
disabled there) - the publish calls are guarded by MQTT_ENABLE and follow the existing
topicTrack/cover patterns.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: fhirschmann

README.md

@@ -148,6 +148,7 @@ neon logo that doubles as the SVG favicon ([`7be5254`](../../commit/7be5254)):
 | **Settings tabs de-cluttered**: the long "General" sub-tab was split — the **LED** settings (NeoPixel brightness + LED config) moved into a new **LEDs** sub-tab, and **Deep sleep + Battery** into a new **Power** sub-tab. Both new tabs are covered by the same auto-save. General now holds just volume/branding/options/playlist/rotary. i18n de/en/fr | [`settings-split`](../../releases/tag/settings-split) |
 | **Folder cover-art fallback**: when a track has no embedded ID3 cover, `/cover` now serves a sidecar image from the track's folder (`cover.jpg`/`.jpeg`/`.png` or `folder.jpg`/`.png`) before falling back to the placeholder icon — so audiobooks/albums with a folder image show art in the Control tab | [`cover-fallback`](../../releases/tag/cover-fallback) |
 | **Most-played cards (listening stats)**: a per-card play counter (incremented when a music card starts a playlist) drives a **most-played** list — the top 3 cards (path + play count) appear in the info dialog next to the daily totals; full top-10 via a new `GET /topcards`. A card's counter is cleared when the card is deleted (no ghost stats). Stored in NVS (`rfidPlayCnt`) | [`stats-topcards`](../../releases/tag/stats-topcards) |
+| **MQTT now-playing metadata**: the ID3 **artist** and **album** are published to MQTT state topics (`track_artist`/`track_album`, alongside the existing `track` title and `cover_changed`) and registered as Home-Assistant discovery sensors, so a broker/Home Assistant sees the current artist & album. Reset per track. | — |
 | **OpenAPI/Swagger spec updated**: the bundled `REST_API.yaml` (served at `/swagger.html`) now documents all fork-added endpoints (`/sync`, `/syncstop`, `/playlist`, `/githubupdate`, `/version`, `/login`, `/logout`, `/security`, `/eqrule(s)`, `/activeequalizer`, `/bluetooth*`, `/sdclean`) and declares the security schemes (`X-API-Key` header / `apikey` query param, or the `ESPUINO_SESSION` login cookie) so the Swagger "Authorize" button works. The web-interface footer links to the Swagger UI (`/swagger.html`) | [`f8298d9`](../../commit/f8298d9) |
 
 #### Feature highlights

src/AudioPlayer.cpp

@@ -194,8 +194,14 @@ void Audio_InfoCallback(Audio::msg_t m) {
 			// get artist / album (ID3 "Artist:"/"Album:" + VORBISCOMMENT "ARTIST="/"ALBUM=")
 			else if (startsWith((char *) m.msg, "Artist") || startsWith((char *) m.msg, "ARTIST=") || startsWith((char *) m.msg, "artist=")) {
 				Audio_SetMeta(gPlayProperties.artist, sizeof(gPlayProperties.artist), (const char *) m.msg);
+#ifdef MQTT_ENABLE
+				publishMqtt(topicTrackArtist, gPlayProperties.artist, false);
+#endif
 			} else if (startsWith((char *) m.msg, "Album") || startsWith((char *) m.msg, "ALBUM=") || startsWith((char *) m.msg, "album=")) {
 				Audio_SetMeta(gPlayProperties.album, sizeof(gPlayProperties.album), (const char *) m.msg);
+#ifdef MQTT_ENABLE
+				publishMqtt(topicTrackAlbum, gPlayProperties.album, false);
+#endif
 			}
 			break;
 		}
@@ -1773,6 +1779,8 @@ void AudioPlayer_ClearCover(void) {
 	Web_SendWebsocketData(0, WebsocketCodeType::CoverImg);
 #ifdef MQTT_ENABLE
 	publishMqtt(topicCoverChanged, "", false);
+	publishMqtt(topicTrackArtist, "", false); // reset now-playing metadata for the next track
+	publishMqtt(topicTrackAlbum, "", false);
 #endif
 }
 

src/Mqtt.cpp

@@ -341,6 +341,8 @@ static void Mqtt_PublishHassDiscovery(void) {
 
 	// sensors
 	mqttHassPublish("sensor", "track", "\"name\":\"Track\",\"icon\":\"mdi:music-note\",\"state_topic\":\"" + String(Mqtt_GetStateTopic(topicTrack)) + "\"");
+	mqttHassPublish("sensor", "track_artist", "\"name\":\"Artist\",\"icon\":\"mdi:account-music\",\"state_topic\":\"" + String(Mqtt_GetStateTopic(topicTrackArtist)) + "\"");
+	mqttHassPublish("sensor", "track_album", "\"name\":\"Album\",\"icon\":\"mdi:album\",\"state_topic\":\"" + String(Mqtt_GetStateTopic(topicTrackAlbum)) + "\"");
 	mqttHassPublish("sensor", "status", "\"name\":\"Status\",\"icon\":\"mdi:play-pause\",\"state_topic\":\"" + String(Mqtt_GetStateTopic(topicPausePlay)) + "\"");
 	mqttHassPublish("sensor", "wifi", "\"name\":\"WiFi signal\",\"device_class\":\"signal_strength\",\"unit_of_measurement\":\"dBm\",\"entity_category\":\"diagnostic\",\"state_topic\":\"" + String(Mqtt_GetStateTopic(topicWiFiRssi)) + "\"");
 	mqttHassPublish("sensor", "firmware", "\"name\":\"Firmware update\",\"icon\":\"mdi:package-up\",\"entity_category\":\"diagnostic\",\"state_topic\":\"" + String(Mqtt_GetStateTopic(topicFirmwareUpdate)) + "\"");
@@ -439,6 +441,8 @@ void mqtt_event_handler(void *handler_args, esp_event_base_t base, int32_t event
 			// Publish current state
 			publishMqtt(topicState, "Online", false);
 			publishMqtt(topicTrack, gPlayProperties.title, false);
+			publishMqtt(topicTrackArtist, gPlayProperties.artist, false);
+			publishMqtt(topicTrackAlbum, gPlayProperties.album, false);
 			publishMqtt(topicCoverChanged, "", false);
 			publishMqtt(topicLoudness, static_cast<uint32_t>(AudioPlayer_GetCurrentVolume()), false);
 			publishMqtt(topicSleepTimer, System_GetSleepTimerTimeStamp(), false);

src/settings.h

@@ -301,6 +301,8 @@
 
 		// Topics (state only)
 		constexpr const char topicTrack[] = "track";          // State: current track info (e.g. "(2/10) /mp3/.../file.mp3")
+		constexpr const char topicTrackArtist[] = "track_artist"; // State: current ID3 artist (empty if none)
+		constexpr const char topicTrackAlbum[] = "track_album";   // State: current ID3 album (empty if none)
 		constexpr const char topicCoverChanged[] = "cover_changed"; // State: indicates cover image may have changed
 		constexpr const char topicState[] = "state";         // State: 'Online' when powering on, 'Offline' when powering off
 		constexpr const char topicCurrentIPv4IP[] = "ipv4";  // State: sends current IPv4 address