diff --git a/docs/SETUP.md b/docs/SETUP.md
index a9cd594..5365ecd 100644
--- a/docs/SETUP.md
+++ b/docs/SETUP.md
@@ -28,6 +28,9 @@ Default local store:
 
 - `Hive` (`USE_HIVE_LOCAL_DB=true` by default)
 - first-run migration imports legacy `shared_preferences` payload when present
+- applies to both:
+  - local product state (`LocalRepository`)
+  - sync queue state (`SyncQueueRepository`)
 
 Optional migration path:
 
diff --git a/docs/progress.md b/docs/progress.md
index af9b482..b9bb867 100644
--- a/docs/progress.md
+++ b/docs/progress.md
@@ -2,6 +2,35 @@
 
 Updated: 2026-02-15
 
+## Latest Milestone (2026-02-15): Sync Queue Storage Adapter + Hive Migration
+
+Extended the storage abstraction approach to sync queue persistence:
+
+- Added sync storage abstraction:
+  - `lib/features/sync/storage/sync_state_store.dart`
+- Added concrete sync stores:
+  - `lib/features/sync/storage/sync_state_store_shared_prefs.dart`
+  - `lib/features/sync/storage/sync_state_store_hive.dart`
+  - `lib/features/sync/storage/sync_state_store_in_memory.dart`
+  - provider wiring: `lib/features/sync/storage/sync_state_store_provider.dart`
+- Refactored sync queue repository:
+  - `lib/features/sync/sync_queue_repository.dart`
+  - no direct `shared_preferences` dependency
+  - store-agnostic read/write path via `SyncStateStore`
+  - one-time migration path from legacy shared prefs sync payload into Hive
+- Updated tests to use explicit in-memory store overrides where deterministic:
+  - `test/features/sync/sync_queue_repository_test.dart`
+  - `test/features/sync/sync_coordinator_test.dart`
+  - `test/features/local/local_repository_test.dart`
+  - `test/features/responsive/responsive_views_smoke_test.dart`
+- Added migration coverage:
+  - `test/features/sync/storage/sync_queue_hive_migration_test.dart`
+
+Validation for this milestone:
+
+- `flutter analyze` -> pass
+- `flutter test` -> pass
+
 ## Latest Milestone (2026-02-15): Local Store Adapter Layer (DB Migration Scaffold)
 
 Implemented a persistence boundary so local app state is no longer tightly coupled to `shared_preferences` internals:
diff --git a/lib/features/sync/storage/sync_state_store.dart b/lib/features/sync/storage/sync_state_store.dart
new file mode 100644
index 0000000..37e8820
--- /dev/null
+++ b/lib/features/sync/storage/sync_state_store.dart
@@ -0,0 +1,18 @@
+/// Raw persisted payload for sync queue state.
+class SyncStateRecord {
+  const SyncStateRecord({required this.rawState});
+
+  final String rawState;
+}
+
+/// Persistence boundary for sync queue metadata and pending changes.
+abstract interface class SyncStateStore {
+  /// Reads stored sync state payload.
+  Future<SyncStateRecord?> read();
+
+  /// Writes sync state payload.
+  Future<void> write({required String rawState});
+
+  /// Clears stored sync state payload.
+  Future<void> clear();
+}
diff --git a/lib/features/sync/storage/sync_state_store_hive.dart b/lib/features/sync/storage/sync_state_store_hive.dart
new file mode 100644
index 0000000..1bce059
--- /dev/null
+++ b/lib/features/sync/storage/sync_state_store_hive.dart
@@ -0,0 +1,46 @@
+import 'package:hive_flutter/hive_flutter.dart';
+import 'package:relationship_saver/features/sync/storage/sync_state_store.dart';
+
+/// Hive-backed sync state store.
+class HiveSyncStateStore implements SyncStateStore {
+  static const String _boxName = 'relationship_saver_sync';
+  static const String _stateKey = 'sync_state_json';
+
+  static bool _initialized = false;
+
+  @override
+  Future<void> clear() async {
+    final Box<dynamic> box = await _openBox();
+    await box.delete(_stateKey);
+  }
+
+  @override
+  Future<SyncStateRecord?> read() async {
+    final Box<dynamic> box = await _openBox();
+    final String? rawState = box.get(_stateKey) as String?;
+    if (rawState == null || rawState.isEmpty) {
+      return null;
+    }
+
+    return SyncStateRecord(rawState: rawState);
+  }
+
+  @override
+  Future<void> write({required String rawState}) async {
+    final Box<dynamic> box = await _openBox();
+    await box.put(_stateKey, rawState);
+  }
+
+  Future<Box<dynamic>> _openBox() async {
+    if (!_initialized) {
+      await Hive.initFlutter();
+      _initialized = true;
+    }
+
+    if (!Hive.isBoxOpen(_boxName)) {
+      return Hive.openBox<dynamic>(_boxName);
+    }
+
+    return Hive.box<dynamic>(_boxName);
+  }
+}
diff --git a/lib/features/sync/storage/sync_state_store_in_memory.dart b/lib/features/sync/storage/sync_state_store_in_memory.dart
new file mode 100644
index 0000000..6b57488
--- /dev/null
+++ b/lib/features/sync/storage/sync_state_store_in_memory.dart
@@ -0,0 +1,19 @@
+import 'package:relationship_saver/features/sync/storage/sync_state_store.dart';
+
+/// In-memory sync state store for tests.
+class InMemorySyncStateStore implements SyncStateStore {
+  SyncStateRecord? _record;
+
+  @override
+  Future<void> clear() async {
+    _record = null;
+  }
+
+  @override
+  Future<SyncStateRecord?> read() async => _record;
+
+  @override
+  Future<void> write({required String rawState}) async {
+    _record = SyncStateRecord(rawState: rawState);
+  }
+}
diff --git a/lib/features/sync/storage/sync_state_store_provider.dart b/lib/features/sync/storage/sync_state_store_provider.dart
new file mode 100644
index 0000000..8cec632
--- /dev/null
+++ b/lib/features/sync/storage/sync_state_store_provider.dart
@@ -0,0 +1,14 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:relationship_saver/core/config/app_config.dart';
+import 'package:relationship_saver/features/sync/storage/sync_state_store.dart';
+import 'package:relationship_saver/features/sync/storage/sync_state_store_hive.dart';
+import 'package:relationship_saver/features/sync/storage/sync_state_store_shared_prefs.dart';
+
+/// Chooses sync queue persistence backend.
+final Provider<SyncStateStore> syncStateStoreProvider =
+    Provider<SyncStateStore>((Ref ref) {
+      if (AppConfig.useHiveLocalDb) {
+        return HiveSyncStateStore();
+      }
+      return SharedPrefsSyncStateStore();
+    });
diff --git a/lib/features/sync/storage/sync_state_store_shared_prefs.dart b/lib/features/sync/storage/sync_state_store_shared_prefs.dart
new file mode 100644
index 0000000..2ce0195
--- /dev/null
+++ b/lib/features/sync/storage/sync_state_store_shared_prefs.dart
@@ -0,0 +1,32 @@
+import 'package:relationship_saver/features/sync/storage/sync_state_store.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+/// shared_preferences-backed sync state store.
+class SharedPrefsSyncStateStore implements SyncStateStore {
+  SharedPrefsSyncStateStore({this.stateKey = 'sync_queue_state_v1'});
+
+  final String stateKey;
+
+  @override
+  Future<void> clear() async {
+    final SharedPreferences prefs = await SharedPreferences.getInstance();
+    await prefs.remove(stateKey);
+  }
+
+  @override
+  Future<SyncStateRecord?> read() async {
+    final SharedPreferences prefs = await SharedPreferences.getInstance();
+    final String? rawState = prefs.getString(stateKey);
+    if (rawState == null || rawState.isEmpty) {
+      return null;
+    }
+
+    return SyncStateRecord(rawState: rawState);
+  }
+
+  @override
+  Future<void> write({required String rawState}) async {
+    final SharedPreferences prefs = await SharedPreferences.getInstance();
+    await prefs.setString(stateKey, rawState);
+  }
+}
diff --git a/lib/features/sync/sync_queue_repository.dart b/lib/features/sync/sync_queue_repository.dart
index 21864dc..d3a7a02 100644
--- a/lib/features/sync/sync_queue_repository.dart
+++ b/lib/features/sync/sync_queue_repository.dart
@@ -1,27 +1,43 @@
 import 'dart:convert';
 
 import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:relationship_saver/core/config/app_config.dart';
+import 'package:relationship_saver/features/sync/storage/sync_state_store.dart';
+import 'package:relationship_saver/features/sync/storage/sync_state_store_hive.dart';
+import 'package:relationship_saver/features/sync/storage/sync_state_store_provider.dart';
+import 'package:relationship_saver/features/sync/storage/sync_state_store_shared_prefs.dart';
 import 'package:relationship_saver/features/sync/sync_state.dart';
 import 'package:relationship_saver/integrations/backend/models/backend_models.dart';
-import 'package:shared_preferences/shared_preferences.dart';
 
 /// Persists queued local mutations and sync cursor metadata.
 class SyncQueueRepository extends AsyncNotifier<SyncState> {
-  static const String _storageKey = 'sync_queue_state_v1';
-
   @override
   Future<SyncState> build() async {
-    final SharedPreferences prefs = await SharedPreferences.getInstance();
-    final String? raw = prefs.getString(_storageKey);
-    if (raw == null || raw.isEmpty) {
+    final SyncStateStore store = ref.read(syncStateStoreProvider);
+    SyncStateRecord? record = await store.read();
+
+    if ((record == null || record.rawState.isEmpty) &&
+        AppConfig.useHiveLocalDb &&
+        store is HiveSyncStateStore) {
+      final SharedPrefsSyncStateStore legacyStore = SharedPrefsSyncStateStore();
+      final SyncStateRecord? legacy = await legacyStore.read();
+      if (legacy != null && legacy.rawState.isNotEmpty) {
+        await store.write(rawState: legacy.rawState);
+        await legacyStore.clear();
+        record = await store.read();
+      }
+    }
+
+    if (record == null || record.rawState.isEmpty) {
       return SyncState.empty;
     }
 
     try {
-      final Map<String, dynamic> json = jsonDecode(raw) as Map<String, dynamic>;
+      final Map<String, dynamic> json =
+          jsonDecode(record.rawState) as Map<String, dynamic>;
       return SyncState.fromJson(json);
     } on FormatException {
-      await prefs.remove(_storageKey);
+      await store.clear();
       return SyncState.empty;
     }
   }
@@ -121,8 +137,9 @@ class SyncQueueRepository extends AsyncNotifier<SyncState> {
 
   Future<void> _setState(SyncState next) async {
     state = AsyncData<SyncState>(next);
-    final SharedPreferences prefs = await SharedPreferences.getInstance();
-    await prefs.setString(_storageKey, jsonEncode(next.toJson()));
+    await ref
+        .read(syncStateStoreProvider)
+        .write(rawState: jsonEncode(next.toJson()));
   }
 }
 
diff --git a/test/features/local/local_repository_test.dart b/test/features/local/local_repository_test.dart
index 960f8a0..f991bbe 100644
--- a/test/features/local/local_repository_test.dart
+++ b/test/features/local/local_repository_test.dart
@@ -4,6 +4,8 @@ import 'package:relationship_saver/features/local/local_models.dart';
 import 'package:relationship_saver/features/local/local_repository.dart';
 import 'package:relationship_saver/features/local/storage/local_data_store_in_memory.dart';
 import 'package:relationship_saver/features/local/storage/local_data_store_provider.dart';
+import 'package:relationship_saver/features/sync/storage/sync_state_store_in_memory.dart';
+import 'package:relationship_saver/features/sync/storage/sync_state_store_provider.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 
 void main() {
@@ -179,6 +181,7 @@ ProviderContainer _createContainer() {
   return ProviderContainer(
     overrides: [
       localDataStoreProvider.overrideWithValue(InMemoryLocalDataStore()),
+      syncStateStoreProvider.overrideWithValue(InMemorySyncStateStore()),
     ],
   );
 }
diff --git a/test/features/responsive/responsive_views_smoke_test.dart b/test/features/responsive/responsive_views_smoke_test.dart
index 83dea43..5eec92e 100644
--- a/test/features/responsive/responsive_views_smoke_test.dart
+++ b/test/features/responsive/responsive_views_smoke_test.dart
@@ -14,6 +14,8 @@ import 'package:relationship_saver/features/people/people_view.dart';
 import 'package:relationship_saver/features/reminders/reminders_view.dart';
 import 'package:relationship_saver/features/settings/settings_view.dart';
 import 'package:relationship_saver/features/signals/signals_view.dart';
+import 'package:relationship_saver/features/sync/storage/sync_state_store_in_memory.dart';
+import 'package:relationship_saver/features/sync/storage/sync_state_store_provider.dart';
 import 'package:relationship_saver/features/sync/sync_view.dart';
 import 'package:relationship_saver/integrations/backend/backend_gateway_fake.dart';
 import 'package:relationship_saver/integrations/backend/backend_gateway_provider.dart';
@@ -102,6 +104,7 @@ Future<void> pumpResponsive(
         tokenStoreProvider.overrideWithValue(InMemoryTokenStore()),
         backendGatewayProvider.overrideWithValue(BackendGatewayFake()),
         localDataStoreProvider.overrideWithValue(InMemoryLocalDataStore()),
+        syncStateStoreProvider.overrideWithValue(InMemorySyncStateStore()),
       ],
       child: MaterialApp(theme: AppTheme.light(), home: home),
     ),
diff --git a/test/features/sync/storage/sync_queue_hive_migration_test.dart b/test/features/sync/storage/sync_queue_hive_migration_test.dart
new file mode 100644
index 0000000..1c74e60
--- /dev/null
+++ b/test/features/sync/storage/sync_queue_hive_migration_test.dart
@@ -0,0 +1,81 @@
+import 'dart:convert';
+
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:relationship_saver/features/sync/storage/sync_state_store.dart';
+import 'package:relationship_saver/features/sync/storage/sync_state_store_hive.dart';
+import 'package:relationship_saver/features/sync/storage/sync_state_store_provider.dart';
+import 'package:relationship_saver/features/sync/storage/sync_state_store_shared_prefs.dart';
+import 'package:relationship_saver/features/sync/sync_queue_repository.dart';
+import 'package:relationship_saver/integrations/backend/models/backend_models.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+void main() {
+  setUp(() {
+    SharedPreferences.setMockInitialValues(<String, Object>{});
+  });
+
+  test(
+    'migrates legacy shared prefs sync queue payload into hive store',
+    () async {
+      final SyncStateRecord legacyRecord = SyncStateRecord(
+        rawState: jsonEncode(<String, dynamic>{
+          'cursor': 'legacy-cursor',
+          'pendingChanges': <Map<String, dynamic>>[
+            ChangeEnvelope(
+              schemaVersion: 1,
+              entityType: 'person',
+              entityId: 'legacy-person',
+              op: ChangeOperation.upsert,
+              modifiedAt: DateTime(2026, 2, 15, 10).toUtc(),
+              clientMutationId: 'legacy-cm-1',
+              payload: const <String, dynamic>{'name': 'Legacy'},
+            ).toJson(),
+          ],
+          'lastSyncAt': null,
+          'lastAttemptAt': null,
+          'lastError': null,
+          'lastRejected': <Map<String, dynamic>>[],
+        }),
+      );
+
+      final SharedPrefsSyncStateStore legacyStore = SharedPrefsSyncStateStore();
+      await legacyStore.write(rawState: legacyRecord.rawState);
+
+      final _FakeHiveSyncStore hiveStore = _FakeHiveSyncStore();
+      final ProviderContainer container = ProviderContainer(
+        overrides: [syncStateStoreProvider.overrideWithValue(hiveStore)],
+      );
+      addTearDown(container.dispose);
+
+      final state = await container.read(syncQueueRepositoryProvider.future);
+
+      expect(state.cursor, 'legacy-cursor');
+      expect(state.pendingChanges.length, 1);
+      expect(state.pendingChanges.first.clientMutationId, 'legacy-cm-1');
+
+      final SyncStateRecord? migrated = await hiveStore.read();
+      expect(migrated, isNotNull);
+
+      final SyncStateRecord? legacyAfter = await legacyStore.read();
+      expect(legacyAfter, isNull);
+    },
+  );
+}
+
+class _FakeHiveSyncStore extends HiveSyncStateStore {
+  SyncStateRecord? _record;
+
+  @override
+  Future<void> clear() async {
+    _record = null;
+  }
+
+  @override
+  Future<SyncStateRecord?> read() async => _record;
+
+  @override
+  Future<void> write({required String rawState}) async {
+    _record = SyncStateRecord(rawState: rawState);
+  }
+}
diff --git a/test/features/sync/sync_coordinator_test.dart b/test/features/sync/sync_coordinator_test.dart
index 522a1f3..af0b95e 100644
--- a/test/features/sync/sync_coordinator_test.dart
+++ b/test/features/sync/sync_coordinator_test.dart
@@ -3,6 +3,8 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:relationship_saver/features/local/local_repository.dart';
 import 'package:relationship_saver/features/local/storage/local_data_store_in_memory.dart';
 import 'package:relationship_saver/features/local/storage/local_data_store_provider.dart';
+import 'package:relationship_saver/features/sync/storage/sync_state_store_in_memory.dart';
+import 'package:relationship_saver/features/sync/storage/sync_state_store_provider.dart';
 import 'package:relationship_saver/features/sync/sync_coordinator.dart';
 import 'package:relationship_saver/features/sync/sync_queue_repository.dart';
 import 'package:relationship_saver/features/sync/sync_state.dart';
@@ -21,6 +23,7 @@ void main() {
       overrides: [
         backendGatewayProvider.overrideWithValue(_TestGateway()),
         localDataStoreProvider.overrideWithValue(InMemoryLocalDataStore()),
+        syncStateStoreProvider.overrideWithValue(InMemorySyncStateStore()),
       ],
     );
     addTearDown(container.dispose);
@@ -83,6 +86,7 @@ void main() {
           _TestGateway(pullResult: pullResult),
         ),
         localDataStoreProvider.overrideWithValue(InMemoryLocalDataStore()),
+        syncStateStoreProvider.overrideWithValue(InMemorySyncStateStore()),
       ],
     );
     addTearDown(container.dispose);
diff --git a/test/features/sync/sync_queue_repository_test.dart b/test/features/sync/sync_queue_repository_test.dart
index 5d7c091..705d2cf 100644
--- a/test/features/sync/sync_queue_repository_test.dart
+++ b/test/features/sync/sync_queue_repository_test.dart
@@ -1,16 +1,16 @@
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:relationship_saver/features/sync/storage/sync_state_store_in_memory.dart';
+import 'package:relationship_saver/features/sync/storage/sync_state_store_provider.dart';
 import 'package:relationship_saver/features/sync/sync_queue_repository.dart';
 import 'package:relationship_saver/integrations/backend/models/backend_models.dart';
-import 'package:shared_preferences/shared_preferences.dart';
 
 void main() {
-  setUp(() {
-    SharedPreferences.setMockInitialValues(<String, Object>{});
-  });
-
   test('enqueue persists and can be reloaded', () async {
-    final ProviderContainer container = ProviderContainer();
+    final InMemorySyncStateStore store = InMemorySyncStateStore();
+    final ProviderContainer container = ProviderContainer(
+      overrides: [syncStateStoreProvider.overrideWithValue(store)],
+    );
 
     await container
         .read(syncQueueRepositoryProvider.notifier)
@@ -20,7 +20,9 @@ void main() {
 
     container.dispose();
 
-    final ProviderContainer reloaded = ProviderContainer();
+    final ProviderContainer reloaded = ProviderContainer(
+      overrides: [syncStateStoreProvider.overrideWithValue(store)],
+    );
     addTearDown(reloaded.dispose);
     final SyncStateData reloadedState = await _readState(reloaded);
     expect(reloadedState.pending.length, 1);
@@ -30,7 +32,11 @@ void main() {
   test(
     'applyPushResult removes completed mutation ids and tracks rejections',
     () async {
-      final ProviderContainer container = ProviderContainer();
+      final ProviderContainer container = ProviderContainer(
+        overrides: [
+          syncStateStoreProvider.overrideWithValue(InMemorySyncStateStore()),
+        ],
+      );
       addTearDown(container.dispose);
 
       final SyncQueueRepository notifier = container.read(