refactor(extensions): separate domain models from provider state

lib/models/extension.dart

@@ -1,5 +1,3 @@
-part of 'extension_provider.dart';
-
 // Manifest-backed models: extension metadata, capabilities, health, and
 // install results.
 
@@ -17,39 +15,6 @@ class ExtensionRestoreResult {
   });
 }
 
-bool _stringListEquals(List<String> a, List<String> b) {
-  if (identical(a, b)) return true;
-  if (a.length != b.length) return false;
-  for (var i = 0; i < a.length; i++) {
-    if (a[i] != b[i]) return false;
-  }
-  return true;
-}
-
-List<String>? _tryDecodeStringListPreference(String rawJson, String key) {
-  try {
-    final decoded = jsonDecode(rawJson);
-    if (decoded is! List) {
-      throw const FormatException('expected a JSON list');
-    }
-
-    final values = <String>[];
-    for (final item in decoded) {
-      if (item is! String) {
-        throw const FormatException('expected string entries');
-      }
-      final trimmed = item.trim();
-      if (trimmed.isNotEmpty) {
-        values.add(trimmed);
-      }
-    }
-    return values;
-  } catch (e) {
-    _log.w('Ignoring invalid $key preference: $e');
-    return null;
-  }
-}
-
 class ExtensionDownloadTransferPolicy {
   final int maxAttempts;
   final String resumePolicy;

lib/providers/extension_provider.dart

@@ -5,13 +5,15 @@ import 'package:flutter/widgets.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:path_provider/path_provider.dart';
 import 'package:shared_preferences/shared_preferences.dart';
+import 'package:spotiflac_android/models/extension.dart';
 import 'package:spotiflac_android/models/settings.dart';
 import 'package:spotiflac_android/services/platform_bridge.dart';
 import 'package:spotiflac_android/services/extension_storage_service.dart';
 import 'package:spotiflac_android/utils/logger.dart';
 import 'package:spotiflac_android/providers/settings_provider.dart';
 
-part 'extension_models.dart';
+export 'package:spotiflac_android/models/extension.dart';
+
 part 'extension_provider_priority.dart';
 
 final _log = AppLogger('ExtensionProvider');

lib/providers/extension_provider_priority.dart

@@ -1,6 +1,39 @@
 // ignore_for_file: invalid_use_of_protected_member, invalid_use_of_visible_for_testing_member
 part of 'extension_provider.dart';
 
+bool _stringListEquals(List<String> a, List<String> b) {
+  if (identical(a, b)) return true;
+  if (a.length != b.length) return false;
+  for (var i = 0; i < a.length; i++) {
+    if (a[i] != b[i]) return false;
+  }
+  return true;
+}
+
+List<String>? _tryDecodeStringListPreference(String rawJson, String key) {
+  try {
+    final decoded = jsonDecode(rawJson);
+    if (decoded is! List) {
+      throw const FormatException('expected a JSON list');
+    }
+
+    final values = <String>[];
+    for (final item in decoded) {
+      if (item is! String) {
+        throw const FormatException('expected string entries');
+      }
+      final trimmed = item.trim();
+      if (trimmed.isNotEmpty) {
+        values.add(trimmed);
+      }
+    }
+    return values;
+  } catch (e) {
+    _log.w('Ignoring invalid $key preference: $e');
+    return null;
+  }
+}
+
 /// Download/metadata/search provider priority: persistence, sanitizing, and
 /// reconciliation when extensions are installed, removed, or toggled.
 extension ExtensionNotifierProviderPriority on ExtensionNotifier {

lib/services/download_metadata_embedding.dart

@@ -4,7 +4,7 @@ import 'dart:math';
 import 'package:path_provider/path_provider.dart';
 import 'package:spotiflac_android/models/settings.dart';
 import 'package:spotiflac_android/models/track.dart';
-import 'package:spotiflac_android/providers/extension_provider.dart';
+import 'package:spotiflac_android/models/extension.dart';
 import 'package:spotiflac_android/services/download_metadata_resolver.dart';
 import 'package:spotiflac_android/services/ffmpeg_service.dart';
 import 'package:spotiflac_android/services/platform_bridge.dart';

lib/services/download_metadata_resolver.dart

@@ -1,6 +1,6 @@
 import 'package:spotiflac_android/models/settings.dart';
 import 'package:spotiflac_android/models/track.dart';
-import 'package:spotiflac_android/providers/extension_provider.dart';
+import 'package:spotiflac_android/models/extension.dart';
 import 'package:spotiflac_android/services/download_album_metadata.dart';
 import 'package:spotiflac_android/services/download_track_metadata.dart';
 import 'package:spotiflac_android/services/platform_bridge.dart';

lib/services/local_track_redownload_service.dart

@@ -1,6 +1,6 @@
 import 'package:spotiflac_android/models/settings.dart';
 import 'package:spotiflac_android/models/track.dart';
-import 'package:spotiflac_android/providers/extension_provider.dart';
+import 'package:spotiflac_android/models/extension.dart';
 import 'package:spotiflac_android/services/library_database.dart';
 import 'package:spotiflac_android/services/platform_bridge.dart';
 

lib/services/metadata_autofill_service.dart

@@ -1,4 +1,4 @@
-import 'package:spotiflac_android/providers/extension_provider.dart';
+import 'package:spotiflac_android/models/extension.dart';
 import 'package:spotiflac_android/services/platform_bridge.dart';
 import 'package:spotiflac_android/utils/logger.dart';