feat(auto): add an Ecualizador browsable folder with preset selection

On-device feedback showed the equalizer's preset-cycling custom action
looked dead: many head units render custom actions icon-first, and a
monochrome icon cannot legibly encode "which of six presets" the way a
browsable list's text rows can.

This adds an "Ecualizador" folder to the car's browse tree, listing
"Desactivar" first, then the six factory presets by name, with the
currently-active one marked. Selecting a preset routes through the same
playFromMediaId seam every other browse-tree leaf already uses; picking
a preset while the equalizer is off turns it on and applies that preset.

Supersedes the earlier "no equalizer folder" rule (commit 2403da3),
which predated this feedback -- see decision auto/ecualizador-diseno.

The preset-cycling custom action still coexists with the folder in this
commit; it is removed in the next one.

lib/l10n/app_ar.arb

@@ -841,5 +841,6 @@
       }
     }
   },
+  "autoEqDisableOption": "تعطيل",
   "alarmCardVacationPausedBadge": "متوقفة مؤقتًا بسبب الإجازة"
 }

lib/l10n/app_bn.arb

@@ -841,5 +841,6 @@
       }
     }
   },
+  "autoEqDisableOption": "বন্ধ করুন",
   "alarmCardVacationPausedBadge": "ছুটির কারণে বিরত"
 }

lib/l10n/app_de.arb

@@ -841,5 +841,6 @@
       }
     }
   },
+  "autoEqDisableOption": "Deaktivieren",
   "alarmCardVacationPausedBadge": "Wegen Urlaub pausiert"
 }

lib/l10n/app_en.arb

@@ -841,5 +841,6 @@
       }
     }
   },
+  "autoEqDisableOption": "Disable",
   "alarmCardVacationPausedBadge": "Paused for vacation"
 }

lib/l10n/app_es.arb

@@ -800,5 +800,6 @@
       }
     }
   },
+  "autoEqDisableOption": "Desactivar",
   "alarmCardVacationPausedBadge": "Pausada por vacaciones"
 }

lib/l10n/app_fr.arb

@@ -841,5 +841,6 @@
       }
     }
   },
+  "autoEqDisableOption": "Désactiver",
   "alarmCardVacationPausedBadge": "En pause pour les vacances"
 }

lib/l10n/app_hi.arb

@@ -841,5 +841,6 @@
       }
     }
   },
+  "autoEqDisableOption": "बंद करें",
   "alarmCardVacationPausedBadge": "छुट्टी के कारण रोका गया"
 }

lib/l10n/app_id.arb

@@ -841,5 +841,6 @@
       }
     }
   },
+  "autoEqDisableOption": "Nonaktifkan",
   "alarmCardVacationPausedBadge": "Dijeda karena liburan"
 }

lib/l10n/app_it.arb

@@ -841,5 +841,6 @@
       }
     }
   },
+  "autoEqDisableOption": "Disattiva",
   "alarmCardVacationPausedBadge": "In pausa per le vacanze"
 }

lib/l10n/app_ja.arb

@@ -841,5 +841,6 @@
       }
     }
   },
+  "autoEqDisableOption": "無効化",
   "alarmCardVacationPausedBadge": "休暇のため一時停止中"
 }

lib/l10n/app_pt.arb

@@ -841,5 +841,6 @@
       }
     }
   },
+  "autoEqDisableOption": "Desativar",
   "alarmCardVacationPausedBadge": "Pausada por férias"
 }

lib/l10n/app_ru.arb

@@ -841,5 +841,6 @@
       }
     }
   },
+  "autoEqDisableOption": "Отключить",
   "alarmCardVacationPausedBadge": "Приостановлено на время отпуска"
 }

lib/l10n/app_zh.arb

@@ -841,5 +841,6 @@
       }
     }
   },
+  "autoEqDisableOption": "关闭",
   "alarmCardVacationPausedBadge": "因假期已暂停"
 }

lib/l10n/gen/app_localizations.dart

@@ -3068,6 +3068,12 @@ abstract class AppLocalizations {
   /// **'Preset: {preset}'**
   String eqCustomActionPresetLabel(String preset);
 
+  /// No description provided for @autoEqDisableOption.
+  ///
+  /// In es, this message translates to:
+  /// **'Desactivar'**
+  String get autoEqDisableOption;
+
   /// No description provided for @alarmCardVacationPausedBadge.
   ///
   /// In es, this message translates to:

lib/l10n/gen/app_localizations_ar.dart

@@ -1688,6 +1688,9 @@ class AppLocalizationsAr extends AppLocalizations {
     return 'الإعداد المسبق: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'تعطيل';
+
   @override
   String get alarmCardVacationPausedBadge => 'متوقفة مؤقتًا بسبب الإجازة';
 }

lib/l10n/gen/app_localizations_bn.dart

@@ -1697,6 +1697,9 @@ class AppLocalizationsBn extends AppLocalizations {
     return 'প্রিসেট: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'বন্ধ করুন';
+
   @override
   String get alarmCardVacationPausedBadge => 'ছুটির কারণে বিরত';
 }

lib/l10n/gen/app_localizations_de.dart

@@ -1710,6 +1710,9 @@ class AppLocalizationsDe extends AppLocalizations {
     return 'Voreinstellung: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'Deaktivieren';
+
   @override
   String get alarmCardVacationPausedBadge => 'Wegen Urlaub pausiert';
 }

lib/l10n/gen/app_localizations_en.dart

@@ -1690,6 +1690,9 @@ class AppLocalizationsEn extends AppLocalizations {
     return 'Preset: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'Disable';
+
   @override
   String get alarmCardVacationPausedBadge => 'Paused for vacation';
 }

lib/l10n/gen/app_localizations_es.dart

@@ -1704,6 +1704,9 @@ class AppLocalizationsEs extends AppLocalizations {
     return 'Preset: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'Desactivar';
+
   @override
   String get alarmCardVacationPausedBadge => 'Pausada por vacaciones';
 }

lib/l10n/gen/app_localizations_fr.dart

@@ -1713,6 +1713,9 @@ class AppLocalizationsFr extends AppLocalizations {
     return 'Préréglage : $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'Désactiver';
+
   @override
   String get alarmCardVacationPausedBadge => 'En pause pour les vacances';
 }

lib/l10n/gen/app_localizations_hi.dart

@@ -1692,6 +1692,9 @@ class AppLocalizationsHi extends AppLocalizations {
     return 'प्रीसेट: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'बंद करें';
+
   @override
   String get alarmCardVacationPausedBadge => 'छुट्टी के कारण रोका गया';
 }

lib/l10n/gen/app_localizations_id.dart

@@ -1700,6 +1700,9 @@ class AppLocalizationsId extends AppLocalizations {
     return 'Prasetel: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'Nonaktifkan';
+
   @override
   String get alarmCardVacationPausedBadge => 'Dijeda karena liburan';
 }

lib/l10n/gen/app_localizations_it.dart

@@ -1712,6 +1712,9 @@ class AppLocalizationsIt extends AppLocalizations {
     return 'Preset attivo: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'Disattiva';
+
   @override
   String get alarmCardVacationPausedBadge => 'In pausa per le vacanze';
 }

lib/l10n/gen/app_localizations_ja.dart

@@ -1643,6 +1643,9 @@ class AppLocalizationsJa extends AppLocalizations {
     return 'プリセット: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => '無効化';
+
   @override
   String get alarmCardVacationPausedBadge => '休暇のため一時停止中';
 }

lib/l10n/gen/app_localizations_pt.dart

@@ -1700,6 +1700,9 @@ class AppLocalizationsPt extends AppLocalizations {
     return 'Predefinição: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'Desativar';
+
   @override
   String get alarmCardVacationPausedBadge => 'Pausada por férias';
 }

lib/l10n/gen/app_localizations_ru.dart

@@ -1704,6 +1704,9 @@ class AppLocalizationsRu extends AppLocalizations {
     return 'Пресет: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'Отключить';
+
   @override
   String get alarmCardVacationPausedBadge => 'Приостановлено на время отпуска';
 }

lib/l10n/gen/app_localizations_zh.dart

@@ -1635,6 +1635,9 @@ class AppLocalizationsZh extends AppLocalizations {
     return '预设：$preset';
   }
 
+  @override
+  String get autoEqDisableOption => '关闭';
+
   @override
   String get alarmCardVacationPausedBadge => '因假期已暂停';
 }

lib/servicios/navegacion_auto.dart

@@ -10,6 +10,7 @@ import '../estado/orden_emisoras.dart';
 import '../modelos/emisora.dart';
 import '../modelos/grupo_favoritos.dart';
 import '../modelos/pista_local.dart';
+import '../modelos/preset_ecualizador.dart';
 import 'musica_local_auto.dart';
 import 'persistencia_tolerante.dart';
 import 'servicio_favoritos.dart';
@@ -19,16 +20,22 @@ import 'servicio_favoritos.dart';
 /// no [NodoLocal] coupling — so a future paged folder type can reuse the
 /// slice arithmetic directly. An empty [items] or a [pagina] beyond the
 /// list's range returns `[]`, never throws.
-List<T> paginaDe<T>(List<T> items, {required int pagina, required int tamano}) =>
-    items.skip(pagina * tamano).take(tamano).toList();
+List<T> paginaDe<T>(
+  List<T> items, {
+  required int pagina,
+  required int tamano,
+}) => items.skip(pagina * tamano).take(tamano).toList();
 
 /// Whether a page after [pagina] exists for a list of [total] elements
 /// (Design ADR-6): `true` iff at least one element remains beyond the
 /// current page's slice. The exact-boundary case
 /// (`total == (pagina + 1) * tamano`) is `false` — nothing remains to
 /// reveal.
-bool hayPaginaSiguiente(int total, {required int pagina, required int tamano}) =>
-    total > (pagina + 1) * tamano;
+bool hayPaginaSiguiente(
+  int total, {
+  required int pagina,
+  required int tamano,
+}) => total > (pagina + 1) * tamano;
 
 /// Browse-tree ordering comparator for a local-music folder's children
 /// (Design "Directories before files", item 1): directories sort before
@@ -83,8 +90,7 @@ bool faviconUsable(String? favicon) {
   // even with an empty host (e.g. `Uri.parse('http://').hasAuthority` is
   // `true`) — check `host.isNotEmpty` explicitly to actually require a
   // non-empty authority host.
-  return (uri.scheme == 'http' || uri.scheme == 'https') &&
-      uri.host.isNotEmpty;
+  return (uri.scheme == 'http' || uri.scheme == 'https') && uri.host.isNotEmpty;
 }
 
 /// Deterministic rotation index over the 4 on-brand fallback arts, same
@@ -98,10 +104,11 @@ int indiceArtePara(String seed) =>
 /// drawable URI selected via [indiceArtePara] over `e.uuid` — the same
 /// on-brand art the phone UI would pick for this station (per-station
 /// parity), never a launcher-icon lookalike.
-String artUriPara(Emisora e) => faviconUsable(e.favicon)
-    ? e.favicon!
-    : 'android.resource://es.freetimelab.pluriwave/drawable/'
-        'station_art_${_nombresArte[indiceArtePara(e.uuid)]}';
+String artUriPara(Emisora e) =>
+    faviconUsable(e.favicon)
+        ? e.favicon!
+        : 'android.resource://es.freetimelab.pluriwave/drawable/'
+            'station_art_${_nombresArte[indiceArtePara(e.uuid)]}';
 
 /// Formats a human-readable audio-quality hint for the browse row's
 /// `displaySubtitle` (Design Decision "`displaySubtitle` quality format"):
@@ -212,6 +219,17 @@ class ConstructorArbolAuto {
   /// (Design "Local root hidden until a folder is configured").
   static const idMusicaLocal = 'musica_local';
 
+  /// Root folder id for the "Ecualizador" browsable folder (decision
+  /// `auto/ecualizador-diseno`): lists "Desactivar" plus the six factory
+  /// presets, the currently-active one marked. Deliberately NOT added to
+  /// [_idsCarpetas] -- like [idMusicaLocal], it has its own dedicated
+  /// children, built by `itemsEcualizadorAuto` in `servicio_audio.dart`
+  /// (which needs `AppLocalizations` -- this pure builder class does not
+  /// depend on it), not the generic station-list [hijos] path. Unlike
+  /// [idMusicaLocal], it is ALWAYS present in [raiz], never conditionally
+  /// hidden.
+  static const idEcualizador = 'ecualizador';
+
   static const _idsCarpetas = {idFavoritos, idTodas, idMisEmisoras};
   static const _maxItemsPorCarpeta = 50;
 
@@ -295,12 +313,23 @@ class ConstructorArbolAuto {
   };
 
   /// The root folders (Favoritos, Todas las emisoras, Mis emisoras,
-  /// optionally Música Local), all non-playable.
+  /// optionally Música Local, Ecualizador), all non-playable.
   ///
-  /// There is deliberately no equalizer folder: EQ is configured on the phone
-  /// only. The car still gets the right sound, because the per-device preset
-  /// is applied automatically when the output device changes — that lives in
-  /// `EstadoEcualizador`, not in this tree.
+  /// Decision `auto/ecualizador-diseno` SUPERSEDES the "no equalizer
+  /// folder" rule that used to live in this doc comment (commit `2403da3`,
+  /// mirroring the redesign mockup's "sin carpeta de ecualizador", turn t4
+  /// line 40). That rule was sound when written, but predated on-device
+  /// feedback showing that Android Auto custom actions don't surface
+  /// enough state for choosing among six presets: a monochrome icon cannot
+  /// legibly encode "which preset", and many head units render a custom
+  /// action icon-first, hiding its label. `Ecualizador` is a real
+  /// browsable folder again: "Desactivar" first, then the six factory
+  /// presets, the active one marked (children built by
+  /// `itemsEcualizadorAuto` in `servicio_audio.dart` -- this class stays
+  /// free of any `AppLocalizations` dependency, unlike that builder).
+  /// Always present, and LAST in the list (after Música Local, when
+  /// included) -- unlike [idMusicaLocal] it is never conditionally hidden.
+  /// Do not "restore" the no-folder rule without re-reading that decision.
   ///
   /// `Música Local` is OMITTED entirely (not just empty) unless
   /// [incluirMusicaLocal] is `true` (Design "Local root hidden until a folder
@@ -311,6 +340,7 @@ class ConstructorArbolAuto {
     _carpeta(idTodas, 'Todas las emisoras'),
     _carpeta(idMisEmisoras, 'Mis emisoras'),
     if (incluirMusicaLocal) _carpeta(idMusicaLocal, 'Música Local'),
+    _carpeta(idEcualizador, 'Ecualizador'),
   ];
 
   MediaItem _carpeta(String id, String titulo) => MediaItem(
@@ -457,10 +487,11 @@ class ConstructorArbolAuto {
     final construir = construirItem ?? _itemLocal;
     final ordenados = [...nodos]..sort(compararNodoLocalParaNavegacion);
     final paginaActual = paginaDe(ordenados, pagina: pagina, tamano: tamano);
-    final docIds = paginaActual
-        .where((n) => !n.esDirectorio)
-        .map((n) => n.documentId)
-        .toList();
+    final docIds =
+        paginaActual
+            .where((n) => !n.esDirectorio)
+            .map((n) => n.documentId)
+            .toList();
     final metadatos = await metadatosDe(docIds);
     final items = paginaActual.map((n) => construir(n, metadatos)).toList();
     if (hayPaginaSiguiente(ordenados.length, pagina: pagina, tamano: tamano)) {
@@ -486,8 +517,7 @@ class ConstructorArbolAuto {
         // (direct or nested), absent for a folder that is genuinely empty
         // even recursively (Spec "Folder has no tracks").
         if (hayContenidoReproducible) _itemReproducirCarpeta(documentIdPadre),
-        if (hayContenidoReproducible)
-          _itemReproducirAleatorio(documentIdPadre),
+        if (hayContenidoReproducible) _itemReproducirAleatorio(documentIdPadre),
         if (ofreceOrdenCalidad(totalPistas))
           _itemModoOrdenCalidad(documentIdPadre),
         if (ofreceBuckets(totalPistas))
@@ -725,10 +755,11 @@ class ConstructorArbolAuto {
     final ordenados = [...buckets[idxBucket].nodos]
       ..sort((a, b) => a.nombre.compareTo(b.nombre));
     final paginaActual = paginaDe(ordenados, pagina: pagina, tamano: tamano);
-    final docIds = paginaActual
-        .where((n) => !n.esDirectorio)
-        .map((n) => n.documentId)
-        .toList();
+    final docIds =
+        paginaActual
+            .where((n) => !n.esDirectorio)
+            .map((n) => n.documentId)
+            .toList();
     final metadatos = await metadatosDe(docIds);
     final items = paginaActual.map((n) => construir(n, metadatos)).toList();
     if (hayPaginaSiguiente(ordenados.length, pagina: pagina, tamano: tamano)) {
@@ -743,20 +774,21 @@ class ConstructorArbolAuto {
     }
     final meta = metadatos[nodo.documentId];
     final tituloMeta = meta?.titulo?.trim();
-    final titulo = (tituloMeta != null && tituloMeta.isNotEmpty)
-        ? tituloMeta
-        : _tituloDesdeNombre(nodo.nombre);
+    final titulo =
+        (tituloMeta != null && tituloMeta.isNotEmpty)
+            ? tituloMeta
+            : _tituloDesdeNombre(nodo.nombre);
     final artUriMeta = meta?.artUri?.trim();
-    final artUri = (artUriMeta != null && artUriMeta.isNotEmpty)
-        ? artUriMeta
-        : artUriLocal(nodo.documentId);
+    final artUri =
+        (artUriMeta != null && artUriMeta.isNotEmpty)
+            ? artUriMeta
+            : artUriLocal(nodo.documentId);
     final artistaMeta = meta?.artista?.trim();
     return MediaItem(
       id: '$_prefijoPista${nodo.documentId}',
       title: titulo,
-      artist: (artistaMeta != null && artistaMeta.isNotEmpty)
-          ? artistaMeta
-          : null,
+      artist:
+          (artistaMeta != null && artistaMeta.isNotEmpty) ? artistaMeta : null,
       playable: true,
       artUri: Uri.parse(artUri),
       displaySubtitle: subtituloCalidadLocal(meta),
@@ -777,15 +809,17 @@ class ConstructorArbolAuto {
     required List<GrupoFavoritos> grupos,
     required List<Emisora> favoritos,
   }) {
-    final carpetas = grupos
-        .where((g) => !g.esSinAsignar)
-        .where((g) => favoritos.any((e) => e.grupoFavoritosId == g.id))
-        .take(_maxGruposPorFavoritos)
-        .map(itemGrupo)
-        .toList();
-    final sinAsignar = favoritos
-        .where((e) => e.grupoFavoritosId == GrupoFavoritos.sinAsignarId)
-        .toList();
+    final carpetas =
+        grupos
+            .where((g) => !g.esSinAsignar)
+            .where((g) => favoritos.any((e) => e.grupoFavoritosId == g.id))
+            .take(_maxGruposPorFavoritos)
+            .map(itemGrupo)
+            .toList();
+    final sinAsignar =
+        favoritos
+            .where((e) => e.grupoFavoritosId == GrupoFavoritos.sinAsignarId)
+            .toList();
     return [...carpetas, ...hijos(idFavoritos, emisoras: sinAsignar)];
   }
 
@@ -801,13 +835,62 @@ class ConstructorArbolAuto {
     if (!esCarpetaGrupo(grupoMediaId)) return const [];
     final id = grupoMediaId.substring(_prefijoGrupo.length);
     if (id.isEmpty) return const [];
-    final miembros = favoritos
-        .where((e) => e.grupoFavoritosId == id)
-        .toList();
+    final miembros = favoritos.where((e) => e.grupoFavoritosId == id).toList();
     if (miembros.isEmpty) return const [];
     final ordenados = ordenarEmisoras(miembros, OrdenEmisoras.calidad);
     return ordenados.take(_maxItemsPorCarpeta).map(itemEmisora).toList();
   }
+
+  /// Equalizer preset-selection media-id prefix (decision
+  /// `auto/ecualizador-diseno`): `eq_preset:<rawPresetName>` for the six
+  /// factory presets, plus the reserved [_valorDesactivarEq] sentinel for
+  /// the "Desactivar" item ([idDesactivarEq]). Collision-free against every
+  /// other prefix/bare id in this class -- diverges from every sibling
+  /// prefix at the very first character ('e' vs 'g'/'c'/'p') and from every
+  /// bare folder id (none of which starts with "eq_preset:").
+  static const _prefijoPresetEq = 'eq_preset:';
+
+  /// Reserved sentinel raw value for the "Desactivar" item under
+  /// [_prefijoPresetEq] (decision `auto/ecualizador-diseno`) -- never
+  /// collides with a real [PresetEcualizador.nombre]; none of the six
+  /// factory presets is named this.
+  static const _valorDesactivarEq = '_off_';
+
+  /// The "Desactivar" item's media id: the reserved [_valorDesactivarEq]
+  /// sentinel under [_prefijoPresetEq].
+  static const idDesactivarEq = '$_prefijoPresetEq$_valorDesactivarEq';
+
+  /// Whether [id] identifies an item under the Ecualizador folder (a
+  /// factory preset OR "Desactivar").
+  bool esPresetEqMediaId(String id) => id.startsWith(_prefijoPresetEq);
+
+  /// Whether [id] is specifically the "Desactivar" item (not a factory
+  /// preset). Only meaningful alongside [esPresetEqMediaId].
+  bool esDesactivarEqMediaId(String id) => id == idDesactivarEq;
+
+  /// Builds a factory preset's selection media id, matched by raw
+  /// (untranslated) [PresetEcualizador.nombre] -- the SAME identity
+  /// [PresetEcualizador.presets] already uses for equality, so a locale
+  /// change never breaks resolution.
+  String idPresetEq(String nombrePreset) => '$_prefijoPresetEq$nombrePreset';
+
+  /// Resolves an `eq_preset:<nombre>` [id] to the matching factory
+  /// [PresetEcualizador] from [presets] (defaults to
+  /// [PresetEcualizador.presets]), comparing by raw `nombre`. Returns
+  /// `null` for the [_valorDesactivarEq] sentinel, an unresolvable name, or
+  /// any id that doesn't match [esPresetEqMediaId] -- never throws.
+  PresetEcualizador? resolverPresetEq(
+    String id, {
+    List<PresetEcualizador>? presets,
+  }) {
+    if (!esPresetEqMediaId(id) || esDesactivarEqMediaId(id)) return null;
+    final nombre = id.substring(_prefijoPresetEq.length);
+    final lista = presets ?? PresetEcualizador.presets;
+    for (final preset in lista) {
+      if (preset.nombre == nombre) return preset;
+    }
+    return null;
+  }
 }
 
 /// Routing seam between a car-tapped `emisora:<uuid>` media id and the
@@ -847,6 +930,43 @@ Future<void> reproducirPorMediaId(
   await reproducir(item);
 }
 
+/// Routing seam for a car-tapped `eq_preset:<...>` media id (decision
+/// `auto/ecualizador-diseno`, mirrors [reproducirPorMediaId]'s seam
+/// shape): dispatches "Desactivar" to [activarEcualizador]`(false)`, and a
+/// resolved factory preset to [aplicarPreset] -- turning the equalizer
+/// back ON via [activarEcualizador]`(true)` AFTERWARDS whenever [activo]
+/// is currently `false`, so tapping a preset while the equalizer is off
+/// both re-enables it AND applies the tapped preset's gains (Spec
+/// "selecting a preset while disabled enables it and applies it"), never
+/// silently just remembering the preset for later. [aplicarPreset] runs
+/// BEFORE the enable check so the native engine only ever pushes gains
+/// once, for the NEW preset -- never once for whatever was active before,
+/// then again for the new one.
+///
+/// A stale/unresolvable id, or any id that doesn't match
+/// [ConstructorArbolAuto.esPresetEqMediaId], is a no-op: neither callback
+/// runs and no exception propagates.
+Future<void> seleccionarPresetEqPorMediaId(
+  String id, {
+  required bool activo,
+  required Future<void> Function(PresetEcualizador) aplicarPreset,
+  required Future<void> Function(bool) activarEcualizador,
+}) async {
+  final constructor = ConstructorArbolAuto();
+  if (!constructor.esPresetEqMediaId(id)) return;
+
+  if (constructor.esDesactivarEqMediaId(id)) {
+    await activarEcualizador(false);
+    return;
+  }
+
+  final preset = constructor.resolverPresetEq(id);
+  if (preset == null) return;
+
+  await aplicarPreset(preset);
+  if (!activo) await activarEcualizador(true);
+}
+
 /// Fallback title (Design "Title = filename minus extension") for a blank
 /// or otherwise empty-after-stripping local filename — hardcoded Spanish,
 /// matching every other car-tree label in this file (`'Favoritos'`,
@@ -904,10 +1024,8 @@ List<NodoLocal> ordenarPorCalidadLocal(
 ) {
   final ordenados = List<NodoLocal>.from(nodos);
   ordenados.sort(
-    (a, b) => compararCalidadLocal(
-      metadatos[a.documentId],
-      metadatos[b.documentId],
-    ),
+    (a, b) =>
+        compararCalidadLocal(metadatos[a.documentId], metadatos[b.documentId]),
   );
   return ordenados;
 }
@@ -948,12 +1066,13 @@ List<BucketLocal> bucketsDe(List<NodoLocal> nodos) {
   final pistas = nodos.where((n) => !n.esDirectorio).toList();
   return _rangosBucket.map((rango) {
     final (etiqueta, desde, hasta) = rango;
-    final coincidencias = pistas.where((n) {
-      final recortado = n.nombre.trim();
-      if (recortado.isEmpty) return false;
-      final letra = recortado[0].toLowerCase();
-      return letra.compareTo(desde) >= 0 && letra.compareTo(hasta) <= 0;
-    }).toList();
+    final coincidencias =
+        pistas.where((n) {
+          final recortado = n.nombre.trim();
+          if (recortado.isEmpty) return false;
+          final letra = recortado[0].toLowerCase();
+          return letra.compareTo(desde) >= 0 && letra.compareTo(hasta) <= 0;
+        }).toList();
     return BucketLocal(etiqueta: etiqueta, nodos: coincidencias);
   }).toList();
 }
@@ -1119,9 +1238,10 @@ Future<void> reproducirCarpetaLocal(
   }
 
   final recolectadas = await pistasRecursivas(documentId, fuente: fuente);
-  final pistas = aleatorio
-      ? mezclarFisherYates(recolectadas, rng ?? Random())
-      : recolectadas;
+  final pistas =
+      aleatorio
+          ? mezclarFisherYates(recolectadas, rng ?? Random())
+          : recolectadas;
   if (pistas.isEmpty) return;
 
   await iniciarCola(pistas);

lib/servicios/servicio_audio.dart

@@ -66,7 +66,10 @@ void registrarFuenteMusicaLocal(FuenteMusicaLocalAuto fuente) {
 /// the browse tree and the car-tap path already show, instead of a blank
 /// tile on the car/lockscreen/notification. Pure — no [PluriWaveAudioHandler]
 /// dependency — so it is unit-testable without instantiating the handler.
-MediaItem mediaItemParaEmisora(Emisora emisora, {required AppLocalizations l10n}) {
+MediaItem mediaItemParaEmisora(
+  Emisora emisora, {
+  required AppLocalizations l10n,
+}) {
   return MediaItem(
     id: emisora.url,
     title: localizedStationName(l10n, emisora.nombre),
@@ -180,12 +183,12 @@ List<MediaControl> controlesEcualizadorPersonalizados({
   if (!disponible) return const [];
   return [
     MediaControl.custom(
-      androidIcon: activo
-          ? 'drawable/ic_auto_eq_on'
-          : 'drawable/ic_auto_eq_off',
-      label: activo
-          ? l10n.eqCustomActionDisableLabel
-          : l10n.eqCustomActionEnableLabel,
+      androidIcon:
+          activo ? 'drawable/ic_auto_eq_on' : 'drawable/ic_auto_eq_off',
+      label:
+          activo
+              ? l10n.eqCustomActionDisableLabel
+              : l10n.eqCustomActionEnableLabel,
       name: accionEqToggle,
     ),
     MediaControl.custom(
@@ -198,6 +201,85 @@ List<MediaControl> controlesEcualizadorPersonalizados({
   ];
 }
 
+/// Content-style extras for the Ecualizador folder's items (decision
+/// `auto/ecualizador-diseno`), mirrors `ConstructorArbolAuto
+/// ._contentStyleLista` in `navegacion_auto.dart` — duplicated rather than
+/// exposed publicly (see [nombrePresetVisible]'s doc for why small pieces
+/// are deliberately duplicated across this handler/service layer and the
+/// pure browse-tree builder layer rather than cross-layer-shared). List
+/// style, not grid: these items are short text options with no artwork of
+/// their own, unlike a station or local-track tile.
+const _contentStyleListaEq = {
+  'android.media.browse.CONTENT_STYLE_BROWSABLE_HINT': 1,
+  'android.media.browse.CONTENT_STYLE_PLAYABLE_HINT': 1,
+};
+
+/// Marks the active Ecualizador-folder item by prefixing [titulo] with a
+/// checkmark glyph (decision `auto/ecualizador-diseno`, spec "the active
+/// preset must be visibly marked").
+///
+/// A `MediaItem.extras` completion-status flag (`androidx.media.utils.
+/// MediaConstants.DESCRIPTION_EXTRAS_KEY_COMPLETION_STATUS`) was considered
+/// and REJECTED as the marking mechanism: this project's `audio_service`
+/// version (0.18.18) has no Dart wrapper for it — only `AndroidContentStyle`
+/// 's list/grid hints are exposed — and the raw platform key itself is
+/// designed for playback-COMPLETION tracking (e.g. "this podcast episode
+/// was already listened to"), not item SELECTION; repurposing it here could
+/// render as "already played" on some head units, which would be actively
+/// misleading for a preset picker, and there is no way to verify its actual
+/// rendering on a real head unit from this environment. A plain-text
+/// marker renders identically and unambiguously on every head unit, which
+/// an unverifiable, semantically-mismatched extras key cannot guarantee.
+String _marcarActivoEq(String titulo, {required bool activo}) =>
+    activo ? '✓ $titulo' : titulo;
+
+/// Builds the "Ecualizador" folder's children for the Android Auto browse
+/// tree (decision `auto/ecualizador-diseno`): "Desactivar" FIRST, then the
+/// six factory presets in [PresetEcualizador.presets] order, each localized
+/// via [nombrePresetVisible] — the SAME helper the toggle's custom-action
+/// label already uses, so a preset's name reads identically whether the
+/// driver sees it in the now-playing screen's tooltip or in this folder.
+/// All items are playable: tapping one is dispatched through
+/// `playFromMediaId` -> `seleccionarPresetEqPorMediaId` (`navegacion_auto.
+/// dart`), the same seam every other browse-tree leaf already uses; this
+/// folder has no sub-browsing. Exactly one item is marked active via
+/// [_marcarActivoEq]: "Desactivar" when [activo] is `false`, otherwise
+/// whichever preset equals [presetActual] — never both at once, and never
+/// zero once this function is reached (an unresolvable [presetActual] with
+/// [activo] `true` simply marks nothing, which cannot happen in practice
+/// since [presetActual] always originates from [PresetEcualizador.presets]
+/// or a "Personalizado" tweak that would just leave every item unmarked
+/// rather than mis-marking one).
+List<MediaItem> itemsEcualizadorAuto({
+  required bool activo,
+  required PresetEcualizador presetActual,
+  required AppLocalizations l10n,
+}) {
+  final constructor = ConstructorArbolAuto();
+  final items = <MediaItem>[
+    MediaItem(
+      id: ConstructorArbolAuto.idDesactivarEq,
+      title: _marcarActivoEq(l10n.autoEqDisableOption, activo: !activo),
+      playable: true,
+      extras: _contentStyleListaEq,
+    ),
+  ];
+  for (final preset in PresetEcualizador.presets) {
+    items.add(
+      MediaItem(
+        id: constructor.idPresetEq(preset.nombre),
+        title: _marcarActivoEq(
+          nombrePresetVisible(l10n, preset.nombre),
+          activo: activo && preset == presetActual,
+        ),
+        playable: true,
+        extras: _contentStyleListaEq,
+      ),
+    );
+  }
+  return items;
+}
+
 /// Wrapper de alto nivel para el UI.
 class ServicioAudio {
   PluriWaveAudioHandler get _handler {
@@ -1158,6 +1240,17 @@ class PluriWaveAudioHandler extends BaseAudioHandler
         fuente: fuenteLocal,
       );
       if (musicaLocal != null) return musicaLocal;
+      // Ecualizador folder (decision `auto/ecualizador-diseno`): needs no
+      // external data source, unlike every branch below it -- checked
+      // before the `_fuenteNavegacionGlobal` gate, mirroring how the
+      // local-music branch above is also resolved before that gate.
+      if (parentMediaId == ConstructorArbolAuto.idEcualizador) {
+        return itemsEcualizadorAuto(
+          activo: _ecualizadorActivo,
+          presetActual: _presetActual,
+          l10n: _textos,
+        );
+      }
       final fuente = _fuenteNavegacionGlobal;
       if (fuente == null) return const [];
       if (parentMediaId == ConstructorArbolAuto.idFavoritos) {
@@ -1228,14 +1321,24 @@ class PluriWaveAudioHandler extends BaseAudioHandler
         if (fuenteLocal == null) return;
         await reproducirCarpetaLocal(
           mediaId,
-          aleatorio: constructorArbol.esCarpetaLocalAleatorioMediaId(
-            mediaId,
-          ),
+          aleatorio: constructorArbol.esCarpetaLocalAleatorioMediaId(mediaId),
           fuente: fuenteLocal,
           iniciarCola: _iniciarColaLocal,
         );
         return;
       }
+      // Equalizer preset selection (decision `auto/ecualizador-diseno`):
+      // THIRD branch, same unconditional-return shape as the two above --
+      // an `eq_preset:` id never falls through to station routing.
+      if (constructorArbol.esPresetEqMediaId(mediaId)) {
+        await seleccionarPresetEqPorMediaId(
+          mediaId,
+          activo: _ecualizadorActivo,
+          aplicarPreset: aplicarPreset,
+          activarEcualizador: setEcualizadorActivo,
+        );
+        return;
+      }
       final fuente = _fuenteNavegacionGlobal;
       if (fuente == null) return;
       await reproducirPorMediaId(