refactor: streamline settings bindings

lib/providers/shader_provider.dart

@@ -9,7 +9,9 @@ import '../services/shader_asset_loader.dart';
 ///
 /// Persists the selected shader preset so it is restored across sessions.
 class ShaderProvider extends ChangeNotifier with DisposableChangeNotifierMixin {
-  late SettingsService _settingsService;
+  SettingsService? _settingsService;
+  ValueNotifier<String>? _savedPresetListenable;
+  ValueNotifier<List<Map<String, dynamic>>>? _customPresetsListenable;
 
   ShaderPreset _savedPreset = ShaderPreset.none;
   ShaderPreset _currentPreset = ShaderPreset.none;
@@ -21,13 +23,31 @@ class ShaderProvider extends ChangeNotifier with DisposableChangeNotifierMixin {
   }
 
   Future<void> _initialize() async {
-    _settingsService = await SettingsService.getInstance();
+    final service = await SettingsService.getInstance();
+    if (_settingsService == service && _savedPresetListenable != null && _customPresetsListenable != null) {
+      _syncFromSettings();
+      return;
+    }
 
-    // Load custom presets from storage
-    final customData = _settingsService.read(SettingsService.customShaderPresets);
-    _customPresets = customData.map((json) => ShaderPreset.fromJson(json)).toList();
+    _savedPresetListenable?.removeListener(_onSettingsChanged);
+    _customPresetsListenable?.removeListener(_onSettingsChanged);
+    _settingsService = service;
+    _savedPresetListenable = service.listenable(SettingsService.globalShaderPreset)..addListener(_onSettingsChanged);
+    _customPresetsListenable = service.listenable(SettingsService.customShaderPresets)..addListener(_onSettingsChanged);
+    _syncFromSettings();
+  }
 
-    final presetId = _settingsService.read(SettingsService.globalShaderPreset);
+  void _onSettingsChanged() => _syncFromSettings();
+
+  void _syncFromSettings() {
+    final service = _settingsService;
+    if (service == null) return;
+
+    final customData = service.read(SettingsService.customShaderPresets);
+    final customPresets = customData.map((json) => ShaderPreset.fromJson(json)).toList();
+    _customPresets = customPresets;
+
+    final presetId = service.read(SettingsService.globalShaderPreset);
     _savedPreset = findPresetById(presetId) ?? ShaderPreset.none;
     _currentPreset = _savedPreset;
 
@@ -35,6 +55,13 @@ class ShaderProvider extends ChangeNotifier with DisposableChangeNotifierMixin {
     safeNotifyListeners();
   }
 
+  @override
+  void dispose() {
+    _savedPresetListenable?.removeListener(_onSettingsChanged);
+    _customPresetsListenable?.removeListener(_onSettingsChanged);
+    super.dispose();
+  }
+
   /// Whether the provider has finished initializing
   bool get initialized => _initialized;
 
@@ -61,10 +88,13 @@ class ShaderProvider extends ChangeNotifier with DisposableChangeNotifierMixin {
 
   /// Apply and persist a shader preset
   Future<void> setPreset(ShaderPreset preset) async {
-    _savedPreset = preset;
-    _currentPreset = preset;
-    await _settingsService.write(SettingsService.globalShaderPreset, preset.id);
-    safeNotifyListeners();
+    final service = _settingsService ?? await SettingsService.getInstance();
+    await service.write(SettingsService.globalShaderPreset, preset.id);
+    if (_savedPresetListenable == null) {
+      _savedPreset = preset;
+      _currentPreset = preset;
+      safeNotifyListeners();
+    }
   }
 
   /// Update the current preset without persisting (e.g. toggling off temporarily)
@@ -85,12 +115,12 @@ class ShaderProvider extends ChangeNotifier with DisposableChangeNotifierMixin {
 
     _customPresets.add(preset);
     await _saveCustomPresets();
-    safeNotifyListeners();
     return preset;
   }
 
   /// Delete a custom shader preset and its file.
   Future<void> deleteCustomShader(ShaderPreset preset) async {
+    final wasActive = _currentPreset.id == preset.id || _savedPreset.id == preset.id;
     if (preset.fileName != null) {
       await ShaderAssetLoader.deleteCustomShader(preset.fileName!);
     }
@@ -98,18 +128,15 @@ class ShaderProvider extends ChangeNotifier with DisposableChangeNotifierMixin {
     await _saveCustomPresets();
 
     // Reset to none if the deleted preset was active
-    if (_currentPreset.id == preset.id || _savedPreset.id == preset.id) {
-      _savedPreset = ShaderPreset.none;
-      _currentPreset = ShaderPreset.none;
-      await _settingsService.write(SettingsService.globalShaderPreset, ShaderPreset.none.id);
+    if (wasActive) {
+      await setPreset(ShaderPreset.none);
     }
-
-    safeNotifyListeners();
   }
 
   Future<void> _saveCustomPresets() async {
+    final service = _settingsService ?? await SettingsService.getInstance();
     final data = _customPresets.map((p) => p.toJson()).toList();
-    await _settingsService.write(SettingsService.customShaderPresets, data);
+    await service.write(SettingsService.customShaderPresets, data);
   }
 
   /// Reset to default (no shaders)