fix(eq): re-apply equalizer when the native audio session rotates

ExoPlayer assigns a new audio session id after transient audio-focus
interruptions (navigation prompts, radar warnings), leaving the
AndroidEqualizer attached to the dead session so playback resumed
without equalization until the next station switch. The session-id
listener now detects genuine rotations through a dedicated guard and
re-activates the equalizer with the current preset, gated on EQ
availability to stay clear of player teardown/rebuild.

lib/servicios/servicio_audio.dart

@@ -3,6 +3,7 @@ import 'dart:developer' as developer;
 import 'dart:ui' show Locale;
 
 import 'package:audio_service/audio_service.dart';
+import 'package:flutter/foundation.dart' show visibleForTesting;
 import 'package:just_audio/just_audio.dart';
 
 import '../l10n/display_names.dart';
@@ -159,6 +160,12 @@ class PluriWaveAudioHandler extends BaseAudioHandler
   StreamSubscription<int?>? _androidAudioSessionIdSub;
   final _androidAudioSessionIdController = StreamController<int?>.broadcast();
   int? _androidAudioSessionId;
+
+  /// Last session id processed for EQ re-apply purposes (Design "Change-guard
+  /// field separate from broadcast field"). Kept apart from
+  /// [_androidAudioSessionId] so external broadcast semantics on
+  /// [androidAudioSessionIdStream] stay untouched by the EQ re-apply guard.
+  int? _ultimaSessionIdEq;
   Future<void> _colaCambioFuente = Future<void>.value();
   int _revisionFuente = 0;
 
@@ -262,6 +269,14 @@ class PluriWaveAudioHandler extends BaseAudioHandler
       if (!_androidAudioSessionIdController.isClosed) {
         _androidAudioSessionIdController.add(sessionId);
       }
+      if (debeReaplicarEcualizador(
+        sessionId: sessionId,
+        ultimaSessionIdEq: _ultimaSessionIdEq,
+        eqDisponible: _eqDisponible,
+      )) {
+        _ultimaSessionIdEq = sessionId;
+        unawaited(_activarEcualizador());
+      }
     });
   }
 
@@ -502,6 +517,7 @@ class PluriWaveAudioHandler extends BaseAudioHandler
     _eq = AndroidEqualizer();
     _eqDisponible = false;
     _androidAudioSessionId = null;
+    _ultimaSessionIdEq = null;
     _player = _crearPlayer();
     await _player.setVolume(_volumenEfectivo);
     _conectarStreamsPlayer();
@@ -536,6 +552,19 @@ class PluriWaveAudioHandler extends BaseAudioHandler
     }
   }
 
+  /// Pure re-apply decision for a native session-id emission. No side effects.
+  ///
+  /// Returns `true` when the native audio session id genuinely rotated
+  /// mid-playback (audio-focus ducking by another app) and the equalizer is
+  /// currently attached, meaning the caller should re-attach the EQ and
+  /// re-push the current preset's gains via [_activarEcualizador].
+  @visibleForTesting
+  static bool debeReaplicarEcualizador({
+    required int? sessionId,
+    required int? ultimaSessionIdEq,
+    required bool eqDisponible,
+  }) => sessionId != null && sessionId != ultimaSessionIdEq && eqDisponible;
+
   /// Aplica un preset al ecualizador nativo Android.
   Future<void> aplicarPreset(PresetEcualizador preset) async {
     _presetActual = preset;