feat: Implement note encryption and synchronization features

- Added NoteEncryption class for encrypting and decrypting note content using AES-GCM.
- Updated NoteRepository to handle synchronization of notes and categories with the server, including encryption of note data before sending.
- Introduced SyncRequest and SyncResponse models for managing synchronization data.
- Enhanced LocalVaultService to store and retrieve the encryption key.
- Modified HomeScreen and SettingsScreen to trigger synchronization after note operations and manage API endpoint settings.
- Added SyncStatusIndicator to provide visual feedback on synchronization status in the app title bar.
- Created Category model to manage note categories with encryption support.
- Updated note model to include UUID, server version, deletion status, and category ID.
- Added necessary UI elements for displaying and managing the encryption key in SettingsScreen.
- Updated dependencies in pubspec.yaml for cryptography and HTTP handling.

lib/app.dart

@@ -2,7 +2,9 @@ import 'dart:async';
 import 'dart:io';
 
 import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
 import 'package:notas/data/app_database.dart';
+import 'package:notas/data/api_client.dart';
 import 'package:notas/data/local_vault_service.dart';
 import 'package:notas/data/note_repository.dart';
 import 'package:notas/platform/app_platform.dart';
@@ -14,6 +16,7 @@ import 'package:notas/screens/settings_screen.dart';
 import 'package:notas/screens/vault_access_screen.dart';
 import 'package:notas/theme/app_theme.dart';
 import 'package:notas/widgets/app_title_bar.dart';
+import 'package:notas/widgets/sync_status_indicator.dart';
 import 'package:path/path.dart' as p;
 import 'package:path_provider/path_provider.dart';
 import 'package:window_manager/window_manager.dart';
@@ -31,6 +34,10 @@ enum _AppPhase {
   notes,
 }
 
+class PerformSyncIntent extends Intent {
+  const PerformSyncIntent();
+}
+
 class NotesApp extends StatefulWidget {
   const NotesApp({super.key});
 
@@ -42,6 +49,7 @@ class _NotesAppState extends State<NotesApp>
     with WindowListener, WidgetsBindingObserver {
   static const Duration _screenTransitionDuration = Duration(milliseconds: 280);
   static const Duration _biometricInactivityTimeout = Duration(minutes: 5);
+  static const Duration _syncInterval = Duration(minutes: 5);
 
   final LocalVaultService _vaultService = LocalVaultService.instance;
   final GlobalKey<ScaffoldMessengerState> _scaffoldMessengerKey =
@@ -56,9 +64,12 @@ class _NotesAppState extends State<NotesApp>
   bool _biometricGateEnabled = false;
   int _biometricGateSession = 0;
   Timer? _biometricLockTimer;
+  Timer? _syncTimer;
   bool _isHandlingWindowClose = false;
   _AppPhase _phase = _AppPhase.loading;
   _AppSection _currentSection = _AppSection.home;
+  SyncStatus _syncStatus = SyncStatus.idle;
+  String? _syncErrorMessage;
 
   @override
   void initState() {
@@ -79,6 +90,7 @@ class _NotesAppState extends State<NotesApp>
       windowManager.setPreventClose(false);
     }
     _biometricLockTimer?.cancel();
+    _syncTimer?.cancel();
     _database?.close();
     super.dispose();
   }
@@ -179,9 +191,18 @@ class _NotesAppState extends State<NotesApp>
 
       setState(() {
         _database = database;
-        _repository = NoteRepository(database: database);
+        _repository = NoteRepository(
+          database: database,
+          authApi: AuthApi.instance,
+                  masterKey: encryptionKey,
+        );
         _phase = _AppPhase.notes;
       });
+
+      // Start periodic sync
+      _startPeriodicSync();
+      // Run an initial full sync immediately to pull server changes
+      unawaited(_performSync(forceFull: true));
     } catch (e) {
       // If the database file is not a valid SQLite DB (e.g., wrong key or corruption),
       // reset the local vault so the app doesn't crash. The reset will delete DB files
@@ -238,6 +259,86 @@ class _NotesAppState extends State<NotesApp>
     }
   }
 
+  Future<void> _beginRemoteVaultFlow({
+    required String username,
+    required String password,
+    required bool isRegister,
+  }) async {
+    if (_isUnlocking) {
+      return;
+    }
+
+    setState(() {
+      _isUnlocking = true;
+    });
+
+    try {
+      if (isRegister) {
+        final String encryptionKey = _vaultService.generateEncryptionKey();
+        final String encryptedMasterKey =
+            await AuthApi.instance.encryptWithPassword(encryptionKey, password);
+
+        final Map<String, dynamic> response = await AuthApi.instance.register(
+          username,
+          password,
+          encryptedMasterKey: encryptedMasterKey,
+        );
+
+        if (response['error'] == true) {
+          throw StateError('No se pudo registrar el usuario.');
+        }
+
+        await _vaultService.storeEncryptionKey(encryptionKey);
+        _pendingEncryptionKey = encryptionKey;
+      } else {
+        final Map<String, dynamic> response = await AuthApi.instance.login(
+          username,
+          password,
+        );
+
+        if (response['error'] == true) {
+          throw StateError('No se pudo iniciar sesión.');
+        }
+
+        final String? encryptedMasterKey =
+            (response['encrypted_master_key'] as String?) ??
+            (response['encryptedMasterKey'] as String?);
+
+        if (encryptedMasterKey == null || encryptedMasterKey.isEmpty) {
+          throw StateError('La API no devolvió la clave de encriptación.');
+        }
+
+        final String encryptionKey =
+            await AuthApi.instance.decryptWithPassword(encryptedMasterKey, password);
+
+        await _vaultService.storeEncryptionKey(encryptionKey);
+        _pendingEncryptionKey = encryptionKey;
+      }
+
+      await _vaultService.setVaultAccessCompleted(true);
+      await _vaultService.setBiometricChoicePending(true);
+      await _vaultService.setBiometricGateEnabled(false);
+
+      if (mounted) {
+        setState(() {
+          _phase = _AppPhase.biometricChoice;
+          _biometricGateEnabled = false;
+        });
+      }
+    } catch (error) {
+      _scaffoldMessengerKey.currentState?.showSnackBar(
+        SnackBar(content: Text('No se pudo completar la autenticación: $error')),
+      );
+    } finally {
+      if (mounted) {
+        setState(() {
+          _isUnlocking = false;
+          _isBootstrapping = false;
+        });
+      }
+    }
+  }
+
   Future<void> _enterWithoutAccount() {
     return _beginInitialVaultFlow();
   }
@@ -496,6 +597,66 @@ class _NotesAppState extends State<NotesApp>
     await WindowStateStore.instance.saveWindowSize(currentSize);
   }
 
+  void _startPeriodicSync() {
+    _syncTimer?.cancel();
+    _syncTimer = Timer.periodic(_syncInterval, (_) {
+      _performSync();
+    });
+  }
+
+  Future<void> _performSync({bool forceFull = false}) async {
+    if (_repository == null) {
+      return;
+    }
+
+    if (!mounted) {
+      return;
+    }
+
+    setState(() {
+      _syncStatus = SyncStatus.syncing;
+      _syncErrorMessage = null;
+    });
+
+    try {
+      final Map<String, dynamic> result = await _repository!.performSync(forceFull: forceFull);
+
+      if (!mounted) {
+        return;
+      }
+
+      if (result['error'] == true) {
+        setState(() {
+          _syncStatus = SyncStatus.error;
+          _syncErrorMessage = result['message'] as String?;
+        });
+      } else {
+        setState(() {
+          _syncStatus = SyncStatus.synced;
+          _syncErrorMessage = null;
+        });
+
+        // Reset to idle after 3 seconds
+        Future<void>.delayed(const Duration(seconds: 3), () {
+          if (mounted) {
+            setState(() {
+              _syncStatus = SyncStatus.idle;
+            });
+          }
+        });
+      }
+    } catch (e) {
+      if (!mounted) {
+        return;
+      }
+
+      setState(() {
+        _syncStatus = SyncStatus.error;
+        _syncErrorMessage = e.toString();
+      });
+    }
+  }
+
   Widget _buildLoadingScreen() {
     return MaterialApp(
       navigatorKey: _navigatorKey,
@@ -557,8 +718,23 @@ class _NotesAppState extends State<NotesApp>
       debugShowCheckedModeBanner: false,
       scaffoldMessengerKey: _scaffoldMessengerKey,
       theme: AppTheme.theme,
-      home: Scaffold(
+      home: Shortcuts(
-        body: Container(
+        shortcuts: <LogicalKeySet, Intent>{
+          LogicalKeySet(LogicalKeyboardKey.f5): const PerformSyncIntent(),
+        },
+        child: Actions(
+          actions: <Type, Action<Intent>>{
+            PerformSyncIntent: CallbackAction<PerformSyncIntent>(
+              onInvoke: (PerformSyncIntent intent) {
+                _performSync();
+                return null;
+              },
+            ),
+          },
+          child: Focus(
+            autofocus: true,
+            child: Scaffold(
+              body: Container(
           decoration: const BoxDecoration(
             gradient: LinearGradient(
               colors: [
@@ -573,7 +749,10 @@ class _NotesAppState extends State<NotesApp>
           child: SafeArea(
             child: Column(
               children: [
-                const AppTitleBar(),
+                AppTitleBar(
+                  syncStatus: _syncStatus,
+                  syncErrorMessage: _syncErrorMessage,
+                ),
                 Expanded(
                   child: AnimatedSwitcher(
                     duration: _screenTransitionDuration,
@@ -598,6 +777,9 @@ class _NotesAppState extends State<NotesApp>
           ),
         ),
       ),
+    ),
+  ),
+),
     );
   }
 
@@ -669,10 +851,18 @@ class _NotesAppState extends State<NotesApp>
           home: VaultAccessScreen(
             isBusy: _isUnlocking,
             onCreateAccountPressed: (String email, String password) async {
-              await _beginInitialVaultFlow(actionLabel: 'Crear cuenta');
+              await _beginRemoteVaultFlow(
+                username: email,
+                password: password,
+                isRegister: true,
+              );
             },
             onSignInPressed: (String email, String password) async {
-              await _beginInitialVaultFlow(actionLabel: 'Iniciar sesión');
+              await _beginRemoteVaultFlow(
+                username: email,
+                password: password,
+                isRegister: false,
+              );
             },
             onContinueWithoutAccount: _enterWithoutAccount,
           ),

lib/data/api_client.dart

@@ -0,0 +1,332 @@
+import 'dart:convert';
+import 'dart:math';
+
+import 'package:flutter_secure_storage/flutter_secure_storage.dart';
+import 'package:crypto/crypto.dart' as crypto;
+import 'package:cryptography/cryptography.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+import 'package:http/http.dart' as http;
+import 'package:flutter/foundation.dart';
+import 'package:notas/data/sync_models.dart';
+
+class ApiConfig {
+  ApiConfig._();
+
+  static const String _endpointKey = 'api_endpoint_v1';
+
+  /// Default endpoint for local development. Can be overridden by user.
+  static const String defaultEndpoint = 'http://localhost:3000/api';
+
+  static Future<String> getEndpoint() async {
+    final prefs = await SharedPreferences.getInstance();
+    return prefs.getString(_endpointKey) ?? defaultEndpoint;
+  }
+
+  static Future<void> setEndpoint(String endpoint) async {
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.setString(_endpointKey, endpoint);
+  }
+
+  static Future<void> clearEndpoint() async {
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.remove(_endpointKey);
+  }
+}
+
+class AuthApi {
+  AuthApi._();
+
+  static final AuthApi instance = AuthApi._();
+
+  final FlutterSecureStorage _secureStorage = const FlutterSecureStorage();
+
+  static const String _accessTokenKey = 'api_access_token_v1';
+  static const String _refreshTokenKey = 'api_refresh_token_v1';
+  static const int _passwordHashVersion = 1;
+  static const int _kdfIterations = 100000;
+  static final Pbkdf2 _kdf = Pbkdf2(
+    macAlgorithm: Hmac.sha256(),
+    iterations: _kdfIterations,
+    bits: 256,
+  );
+  static final AesGcm _aes = AesGcm.with256bits();
+
+  Future<String?> get accessToken async =>
+      await _secureStorage.read(key: _accessTokenKey);
+
+  Future<String?> get refreshToken async =>
+      await _secureStorage.read(key: _refreshTokenKey);
+
+  Future<void> clearTokens() async {
+    await _secureStorage.delete(key: _accessTokenKey);
+    await _secureStorage.delete(key: _refreshTokenKey);
+  }
+
+  String hashPassword(String password) {
+    return crypto.sha256.convert(utf8.encode(password)).toString();
+  }
+
+  Future<String> encryptWithPassword(
+    String plaintext,
+    String password,
+  ) async {
+    final List<int> salt = _randomBytes(16);
+    final SecretKey secretKey = await _kdf.deriveKey(
+      secretKey: SecretKey(utf8.encode(password)),
+      nonce: salt,
+    );
+
+    final List<int> nonce = _randomBytes(12);
+    final SecretBox box = await _aes.encrypt(
+      utf8.encode(plaintext),
+      secretKey: secretKey,
+      nonce: nonce,
+    );
+
+    return jsonEncode(<String, dynamic>{
+      'v': _passwordHashVersion,
+      'salt': base64Encode(salt),
+      'nonce': base64Encode(box.nonce),
+      'cipherText': base64Encode(box.cipherText),
+      'mac': base64Encode(box.mac.bytes),
+    });
+  }
+
+  Future<String> decryptWithPassword(
+    String encodedBox,
+    String password,
+  ) async {
+    final Map<String, dynamic> payload = jsonDecode(encodedBox) as Map<String, dynamic>;
+    final List<int> salt = base64Decode(payload['salt'] as String);
+    final List<int> nonce = base64Decode(payload['nonce'] as String);
+    final List<int> cipherText = base64Decode(payload['cipherText'] as String);
+    final List<int> macBytes = base64Decode(payload['mac'] as String);
+
+    final SecretKey secretKey = await _kdf.deriveKey(
+      secretKey: SecretKey(utf8.encode(password)),
+      nonce: salt,
+    );
+
+    final SecretBox box = SecretBox(
+      cipherText,
+      nonce: nonce,
+      mac: Mac(macBytes),
+    );
+
+    final List<int> clearText = await _aes.decrypt(
+      box,
+      secretKey: secretKey,
+    );
+
+    return utf8.decode(clearText);
+  }
+
+  Future<Map<String, dynamic>> login(
+    String username,
+    String password, {
+    String? deviceName,
+    String? endpoint,
+  }) async {
+    final String base = endpoint ?? await ApiConfig.getEndpoint();
+    final Uri url = Uri.parse('$base/auth/login');
+
+    final Map<String, dynamic> body = {
+      'username': username,
+      'password': hashPassword(password),
+    };
+
+    if (deviceName != null) body['deviceName'] = deviceName;
+
+    final http.Response res = await http.post(
+      url,
+      headers: {'Content-Type': 'application/json'},
+      body: jsonEncode(body),
+    );
+
+    if (res.statusCode >= 200 && res.statusCode < 300) {
+      final Map<String, dynamic> json =
+          jsonDecode(res.body) as Map<String, dynamic>;
+
+      final String? access = json['accessToken'] as String?;
+      final String? refresh = json['refreshToken'] as String?;
+
+      if (access != null) {
+        await _secureStorage.write(key: _accessTokenKey, value: access);
+      }
+
+      if (refresh != null) {
+        await _secureStorage.write(key: _refreshTokenKey, value: refresh);
+      }
+
+      return json;
+    }
+
+    // Try to decode error body for better diagnostics.
+    try {
+      final dynamic decoded = jsonDecode(res.body);
+      return {'error': true, 'status': res.statusCode, 'body': decoded};
+    } catch (_) {
+      return {'error': true, 'status': res.statusCode, 'body': res.body};
+    }
+  }
+
+  Future<Map<String, dynamic>> register(
+    String username,
+    String password, {
+    String? encryptedMasterKey,
+    String? endpoint,
+  }) async {
+    final String base = endpoint ?? await ApiConfig.getEndpoint();
+    final Uri url = Uri.parse('$base/auth/register');
+
+    final Map<String, dynamic> body = {
+      'username': username,
+      'password': hashPassword(password),
+      'encrypted_master_key': encryptedMasterKey,
+    };
+
+    final http.Response res = await http.post(
+      url,
+      headers: {'Content-Type': 'application/json'},
+      body: jsonEncode(body),
+    );
+
+    if (res.statusCode >= 200 && res.statusCode < 300) {
+      final Map<String, dynamic> json =
+          jsonDecode(res.body) as Map<String, dynamic>;
+
+      final String? access = json['accessToken'] as String?;
+      final String? refresh = json['refreshToken'] as String?;
+
+      if (access != null) {
+        await _secureStorage.write(key: _accessTokenKey, value: access);
+      }
+
+      if (refresh != null) {
+        await _secureStorage.write(key: _refreshTokenKey, value: refresh);
+      }
+
+      return json;
+    }
+
+    try {
+      final dynamic decoded = jsonDecode(res.body);
+      return {'error': true, 'status': res.statusCode, 'body': decoded};
+    } catch (_) {
+      return {'error': true, 'status': res.statusCode, 'body': res.body};
+    }
+  }
+
+  List<int> _randomBytes(int length) {
+    final Random random = Random.secure();
+    return List<int>.generate(length, (_) => random.nextInt(256));
+  }
+
+  // ========== Sync API ==========
+
+  static const String _lastSyncAtKey = 'api_last_sync_at_v1';
+
+  Future<DateTime?> getLastSyncAt() async {
+    final prefs = await SharedPreferences.getInstance();
+    final String? timestamp = prefs.getString(_lastSyncAtKey);
+    if (timestamp == null) return null;
+    return DateTime.tryParse(timestamp);
+  }
+
+  Future<void> setLastSyncAt(DateTime timestamp) async {
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.setString(_lastSyncAtKey, timestamp.toIso8601String());
+  }
+
+  Future<Map<String, dynamic>> sync(
+    SyncRequest syncRequest, {
+    String? endpoint,
+  }) async {
+    final String? token = await accessToken;
+    if (token == null) {
+      return {'error': true, 'message': 'No access token available'};
+    }
+
+    final String base = endpoint ?? await ApiConfig.getEndpoint();
+    final Uri url = Uri.parse('$base/sync');
+
+    final Map<String, String> headers = {
+      'Content-Type': 'application/json',
+      'Authorization': 'Bearer $token',
+    };
+
+    final String bodyJson = jsonEncode(syncRequest.toJson());
+
+    // Log request (mask authorization header)
+    final Map<String, String> logHeaders = Map.from(headers);
+    if (logHeaders.containsKey('Authorization')) {
+      logHeaders['Authorization'] = 'REDACTED';
+    }
+    debugPrint('SYNC REQUEST -> POST $url');
+    debugPrint('Headers: $logHeaders');
+    debugPrint('Body: $bodyJson');
+
+    final http.Response res = await http.post(
+      url,
+      headers: headers,
+      body: bodyJson,
+    );
+
+    // Log response
+    debugPrint('SYNC RESPONSE <- ${res.statusCode}');
+    debugPrint('Response body: ${res.body}');
+
+    if (res.statusCode >= 200 && res.statusCode < 300) {
+      final Map<String, dynamic> json =
+          jsonDecode(res.body) as Map<String, dynamic>;
+      return {'error': false, 'data': SyncResponse.fromJson(json)};
+    }
+
+    // If token expired (401), try to refresh
+    if (res.statusCode == 401) {
+      final String? refreshTok = await refreshToken;
+      if (refreshTok != null) {
+        final bool refreshed = await _refreshAccessToken(refreshTok, endpoint: endpoint);
+        if (refreshed) {
+          // Retry sync with new token
+          return sync(syncRequest, endpoint: endpoint);
+        }
+      }
+    }
+
+    // Try to decode error body for better diagnostics.
+    try {
+      final dynamic decoded = jsonDecode(res.body);
+      return {'error': true, 'status': res.statusCode, 'body': decoded};
+    } catch (_) {
+      return {'error': true, 'status': res.statusCode, 'body': res.body};
+    }
+  }
+
+  Future<bool> _refreshAccessToken(
+    String refreshToken, {
+    String? endpoint,
+  }) async {
+    final String base = endpoint ?? await ApiConfig.getEndpoint();
+    final Uri url = Uri.parse('$base/auth/refresh');
+
+    final http.Response res = await http.post(
+      url,
+      headers: {'Content-Type': 'application/json'},
+      body: jsonEncode({'refreshToken': refreshToken}),
+    );
+
+    if (res.statusCode >= 200 && res.statusCode < 300) {
+      final Map<String, dynamic> json =
+          jsonDecode(res.body) as Map<String, dynamic>;
+      final String? newAccess = json['accessToken'] as String?;
+
+      if (newAccess != null) {
+        await _secureStorage.write(key: _accessTokenKey, value: newAccess);
+        return true;
+      }
+    }
+
+    return false;
+  }
+}

lib/data/app_database.dart

@@ -7,39 +7,70 @@ import 'package:path_provider/path_provider.dart';
 
 part 'app_database.g.dart';
 
+@DataClassName('DbCategory')
+class Categories extends Table {
+  TextColumn get uuid => text().unique()();
+  TextColumn get encryptedName => text().named('encrypted_name')();
+  IntColumn get serverVersion => integer().named('server_version').withDefault(const Constant(0))();
+    BoolColumn get isDeleted => boolean().named('is_deleted').withDefault(const Constant(false))();
+  DateTimeColumn get updatedAt => dateTime().named('updated_at')();
+
+  @override
+  Set<Column> get primaryKey => {uuid};
+}
+
 @DataClassName('DbNote')
 class Notes extends Table {
   IntColumn get id => integer().autoIncrement()();
+  TextColumn get uuid => text().unique()();
   TextColumn get title => text()();
   TextColumn get body => text()();
-  DateTimeColumn get createdAt => dateTime()();
+  DateTimeColumn get createdAt => dateTime().named('created_at')();
-  DateTimeColumn get updatedAt => dateTime()();
+  DateTimeColumn get updatedAt => dateTime().named('updated_at')();
   IntColumn get sortIndex => integer().named('sort_index')();
+  IntColumn get serverVersion => integer().named('server_version').withDefault(const Constant(0))();
+    BoolColumn get isDeleted => boolean().named('is_deleted').withDefault(const Constant(false))();
+  TextColumn get categoryId => text().nullable().named('category_id')();
 }
 
-@DriftDatabase(tables: [Notes])
+@DriftDatabase(tables: [Notes, Categories])
 class AppDatabase extends _$AppDatabase {
-  AppDatabase({required String encryptionKey}) : super(_openConnection(encryptionKey));
-
   @override
   int get schemaVersion => 1;
+  AppDatabase({required String encryptionKey}) : super(_openConnection(encryptionKey));
 
+  // ========== Categories ==========
+  Future<List<DbCategory>> getAllCategories() {
+    return (select(categories)..where((c) => c.isDeleted.equals(false))).get();
+  }
+
+  Future<int> upsertCategory(CategoriesCompanion category) {
+    return into(categories).insertOnConflictUpdate(category);
+  }
+
+  Future<void> deleteCategory(String uuid) {
+    return (update(categories)..where((c) => c.uuid.equals(uuid)))
+        .write(CategoriesCompanion(isDeleted: Value(true)));
+  }
+
+  // ========== Notes ==========
   Future<List<DbNote>> getAllNotes() {
-    return (select(notes)..orderBy([
+    return (select(notes)
-      (note) => OrderingTerm(expression: note.sortIndex),
+          ..orderBy([(note) => OrderingTerm(expression: note.sortIndex)])
-    ])).get();
+          ..where((n) => n.isDeleted.equals(false)))
+        .get();
   }
 
   Future<int> insertNoteAtTop(NotesCompanion note) {
     return transaction(() async {
-      await customStatement('UPDATE notes SET sort_index = sort_index + 1');
+      await customStatement('UPDATE notes SET sort_index = sort_index + 1 WHERE is_deleted = 0');
       return into(notes).insert(note.copyWith(sortIndex: const Value<int>(0)));
     });
   }
 
   Future<void> replaceAllNotes(List<NotesCompanion> noteList) {
     return transaction(() async {
-      await delete(notes).go();
+      await (delete(notes)..where((n) => n.isDeleted.equals(false))).go();
 
       for (final NotesCompanion note in noteList) {
         await into(notes).insert(note);
@@ -51,17 +82,20 @@ class AppDatabase extends _$AppDatabase {
     return update(notes).replace(note);
   }
 
+  Future<void> deleteNote(int id, int removedIndex) async {
+    await (update(notes)..where((n) => n.id.equals(id))).write(NotesCompanion(isDeleted: Value(true)));
+
+    await customStatement(
+      'UPDATE notes SET sort_index = sort_index - 1 WHERE sort_index > ? AND is_deleted = 0',
+      [removedIndex],
+    );
+  }
+
   Future<void> deleteNoteAndShift({
     required int id,
     required int removedIndex,
   }) {
-    return transaction(() async {
+    return deleteNote(id, removedIndex);
-      await (delete(notes)..where((note) => note.id.equals(id))).go();
-      await customStatement(
-        'UPDATE notes SET sort_index = sort_index - 1 WHERE sort_index > ?',
-        [removedIndex],
-      );
-    });
   }
 
   Future<void> moveNote({
@@ -76,12 +110,12 @@ class AppDatabase extends _$AppDatabase {
     return transaction(() async {
       if (oldIndex < newIndex) {
         await customStatement(
-          'UPDATE notes SET sort_index = sort_index - 1 WHERE sort_index > ? AND sort_index <= ?',
+          'UPDATE notes SET sort_index = sort_index - 1 WHERE sort_index > ? AND sort_index <= ? AND is_deleted = 0',
           [oldIndex, newIndex],
         );
       } else {
         await customStatement(
-          'UPDATE notes SET sort_index = sort_index + 1 WHERE sort_index >= ? AND sort_index < ?',
+          'UPDATE notes SET sort_index = sort_index + 1 WHERE sort_index >= ? AND sort_index < ? AND is_deleted = 0',
           [newIndex, oldIndex],
         );
       }
@@ -92,6 +126,15 @@ class AppDatabase extends _$AppDatabase {
       );
     });
   }
+
+  // ========== Sync helpers ==========
+  Future<List<DbNote>> getUnsyncedNotes() {
+    return (select(notes)..where((n) => n.isDeleted.equals(true) | n.serverVersion.equals(0))).get();
+  }
+
+  Future<List<DbCategory>> getUnsyncedCategories() {
+    return (select(categories)..where((c) => c.isDeleted.equals(true) | c.serverVersion.equals(0))).get();
+  }
 }
 
 LazyDatabase _openConnection(String encryptionKey) {

lib/data/local_vault_service.dart

@@ -74,6 +74,14 @@ class LocalVaultService {
     return _secureStorage.read(key: _encryptionKeyStorageKey);
   }
 
+  Future<void> storeEncryptionKey(String encryptionKey) async {
+    await _secureStorage.write(key: _encryptionKeyStorageKey, value: encryptionKey);
+  }
+
+  String generateEncryptionKey() {
+    return _generateEncryptionKey();
+  }
+
   Future<bool> hasEncryptionKey() async {
     return (await readStoredEncryptionKeyRaw()) != null;
   }
@@ -117,10 +125,7 @@ class LocalVaultService {
   Future<String> createEncryptionKey({bool protectWithBiometrics = false}) async {
     final String encryptionKey = _generateEncryptionKey();
 
-    await _secureStorage.write(
+    await storeEncryptionKey(encryptionKey);
-      key: _encryptionKeyStorageKey,
-      value: encryptionKey,
-    );
 
     // If requested, try to enable biometric protection. Only enable on mobile
     // platforms and only if the authentication succeeds.

lib/data/note_encryption.dart

@@ -0,0 +1,86 @@
+import 'dart:convert';
+import 'dart:math';
+
+import 'package:cryptography/cryptography.dart';
+
+/// Encriptación de contenido de notas usando AES-GCM
+/// Usa una clave derivada del master key del usuario
+class NoteEncryption {
+  static final AesGcm _aes = AesGcm.with256bits();
+  static const int _passwordHashVersion = 1;
+  static const int _kdfIterations = 100000;
+  static final Pbkdf2 _kdf = Pbkdf2(
+    macAlgorithm: Hmac.sha256(),
+    iterations: _kdfIterations,
+    bits: 256,
+  );
+
+  /// Encripta el contenido de una nota usando el master key
+  /// Retorna el contenido encriptado en formato JSON base64
+  static Future<String> encryptNote(
+    String plaintext,
+    String masterKey,
+  ) async {
+    final List<int> salt = _randomBytes(16);
+    final SecretKey secretKey = await _kdf.deriveKey(
+      secretKey: SecretKey(utf8.encode(masterKey)),
+      nonce: salt,
+    );
+
+    final List<int> nonce = _randomBytes(12);
+    final SecretBox box = await _aes.encrypt(
+      utf8.encode(plaintext),
+      secretKey: secretKey,
+      nonce: nonce,
+    );
+
+    return jsonEncode(<String, dynamic>{
+      'v': _passwordHashVersion,
+      'salt': base64Encode(salt),
+      'nonce': base64Encode(box.nonce),
+      'cipherText': base64Encode(box.cipherText),
+      'mac': base64Encode(box.mac.bytes),
+    });
+  }
+
+  /// Desencripta el contenido de una nota usando el master key
+  static Future<String> decryptNote(
+    String encodedBox,
+    String masterKey,
+  ) async {
+    try {
+      final Map<String, dynamic> payload =
+          jsonDecode(encodedBox) as Map<String, dynamic>;
+      final List<int> salt = base64Decode(payload['salt'] as String);
+      final List<int> nonce = base64Decode(payload['nonce'] as String);
+      final List<int> cipherText =
+          base64Decode(payload['cipherText'] as String);
+      final List<int> macBytes = base64Decode(payload['mac'] as String);
+
+      final SecretKey secretKey = await _kdf.deriveKey(
+        secretKey: SecretKey(utf8.encode(masterKey)),
+        nonce: salt,
+      );
+
+      final SecretBox box = SecretBox(
+        cipherText,
+        nonce: nonce,
+        mac: Mac(macBytes),
+      );
+
+      final List<int> clearText = await _aes.decrypt(
+        box,
+        secretKey: secretKey,
+      );
+
+      return utf8.decode(clearText);
+    } catch (e) {
+      throw Exception('Failed to decrypt note: $e');
+    }
+  }
+
+  static List<int> _randomBytes(int length) {
+    final Random random = Random.secure();
+    return List<int>.generate(length, (_) => random.nextInt(256));
+  }
+}

lib/data/note_repository.dart

@@ -1,10 +1,23 @@
+import 'package:drift/drift.dart';
 import 'package:notas/data/app_database.dart';
+import 'package:notas/data/api_client.dart';
+import 'package:notas/data/sync_models.dart';
 import 'package:notas/models/note.dart';
+import 'package:notas/models/category.dart';
 
+import 'package:notas/data/note_encryption.dart';
 class NoteRepository {
-  NoteRepository({required AppDatabase database}) : _database = database;
+  NoteRepository({
+    required AppDatabase database,
+    required AuthApi authApi,
+      required String masterKey,
+    })  : _database = database,
+      _authApi = authApi,
+      _masterKey = masterKey;
 
   final AppDatabase _database;
+  final AuthApi _authApi;
+  final String _masterKey;
 
   Future<List<Note>> loadNotes() async {
     return _loadNotesFromDatabase();
@@ -13,11 +26,15 @@ class NoteRepository {
   Future<Note> createNote(Note note) async {
     final int id = await _database.insertNoteAtTop(
       NotesCompanion.insert(
+        uuid: note.uuid,
         title: note.title,
         body: note.body,
         createdAt: note.createdAt,
         updatedAt: note.updatedAt,
         sortIndex: 0,
+        serverVersion: const Value(0),
+        isDeleted: const Value(false),
+        categoryId: const Value(null),
       ),
     );
 
@@ -30,11 +47,15 @@ class NoteRepository {
     await _database.updateNoteRow(
       DbNote(
         id: noteId,
+        uuid: note.uuid,
         title: note.title,
         body: note.body,
         createdAt: note.createdAt,
         updatedAt: note.updatedAt,
         sortIndex: note.index,
+        serverVersion: note.serverVersion,
+        isDeleted: note.isDeleted,
+        categoryId: note.categoryId,
       ),
     );
 
@@ -60,19 +81,176 @@ class NoteRepository {
     );
   }
 
-  Future<List<Note>> _loadNotesFromDatabase() async {
+  // ========== Sync logic ==========
-    final List<DbNote> rows = await _database.getAllNotes();
+
-    return rows.map(_fromRow).toList();
+  /// Sincroniza notas con el servidor.
+  /// Requiere que el usuario esté autenticado (token válido).
+  Future<Map<String, dynamic>> performSync({bool forceFull = false}) async {
+    try {
+      // Get last sync timestamp
+      final DateTime? lastSync = await _authApi.getLastSyncAt();
+      final DateTime? lastSyncForRequest = forceFull ? DateTime.utc(1970, 1, 1) : lastSync;
+      
+      // Collect pending changes
+      final List<DbNote> unsyncedNotes = await _database.getUnsyncedNotes();
+      final List<DbCategory> unsyncedCategories = await _database.getUnsyncedCategories();
+
+      // Build sync request (note: we send encrypted data, but locally we have plaintext)
+      // Encrypt all notes before sending
+      final List<SyncNotePayload> encryptedNotesPayload = [];
+      for (final dbNote in unsyncedNotes) {
+        final note = _fromDbNote(dbNote);
+        final encryptedTitle = await NoteEncryption.encryptNote(note.title, _masterKey);
+        final encryptedBody = await NoteEncryption.encryptNote(note.body, _masterKey);
+        encryptedNotesPayload.add(
+          SyncNotePayload.fromNote(
+            note,
+            encryptedTitle: encryptedTitle,
+            encryptedBody: encryptedBody,
+          ),
+        );
+      }
+
+      final List<SyncCategoryPayload> categoriesPayload = unsyncedCategories
+          .map((cat) => SyncCategoryPayload.fromCategory(
+                _fromDbCategory(cat),
+              ))
+          .toList();
+
+      final SyncRequest syncRequest = SyncRequest(
+        lastSyncAt: lastSyncForRequest,
+        changes: SyncChanges(
+          categories: categoriesPayload,
+          notes: encryptedNotesPayload,
+        ),
+      );
+
+      // Call sync API
+      final Map<String, dynamic> syncResult =
+          await _authApi.sync(syncRequest);
+
+      if (syncResult['error'] == true) {
+        return {'error': true, 'message': syncResult['body']};
+      }
+
+      final SyncResponse response = syncResult['data'] as SyncResponse;
+
+      // Apply server changes to local database
+      await _applySyncResponse(response);
+
+      // Update lastSyncAt
+      await _authApi.setLastSyncAt(response.serverTimestamp);
+
+      return {
+        'error': false,
+        'synced': response.synced,
+        'notesCount': response.changes.notes.length,
+        'categoriesCount': response.changes.categories.length,
+      };
+    } catch (e) {
+      return {'error': true, 'message': e.toString()};
+    }
   }
 
-  Note _fromRow(DbNote row) {
+  Future<void> _applySyncResponse(SyncResponse response) async {
+    // Apply categories from server
+    for (final SyncCategoryResponse catResponse in response.changes.categories) {
+      await _database.upsertCategory(
+        CategoriesCompanion(
+          uuid: Value(catResponse.id),
+          encryptedName: Value(catResponse.encryptedName),
+          serverVersion: Value(catResponse.serverVersion),
+          isDeleted: Value(catResponse.isDeleted),
+          updatedAt: Value(catResponse.updatedAt),
+        ),
+      );
+    }
+
+    // Apply notes from server
+    for (final SyncNoteResponse noteResponse in response.changes.notes) {
+      final existingNote = await (_database.select(_database.notes)
+            ..where((n) => n.uuid.equals(noteResponse.id)))
+          .getSingleOrNull();
+
+      // Decrypt note content
+      String decryptedTitle = 'Encrypted';
+      String decryptedBody = 'Encrypted';
+      try {
+        decryptedTitle = await NoteEncryption.decryptNote(
+          noteResponse.encryptedTitle,
+          _masterKey,
+        );
+        decryptedBody = await NoteEncryption.decryptNote(
+          noteResponse.encryptedBody,
+          _masterKey,
+        );
+      } catch (e) {
+        // If decryption fails, keep default encrypted placeholders
+        print('Failed to decrypt note ${noteResponse.id}: $e');
+      }
+
+      if (existingNote != null) {
+        // Update existing note
+        await _database.updateNoteRow(
+          DbNote(
+            id: existingNote.id,
+            uuid: noteResponse.id,
+            title: decryptedTitle,
+            body: decryptedBody,
+            createdAt: existingNote.createdAt,
+            updatedAt: noteResponse.updatedAt,
+            sortIndex: noteResponse.position,
+            serverVersion: noteResponse.serverVersion,
+            isDeleted: noteResponse.isDeleted,
+            categoryId: noteResponse.categoryId,
+          ),
+        );
+      } else {
+        // Insert new note
+        await _database.into(_database.notes).insert(
+              NotesCompanion(
+                uuid: Value(noteResponse.id),
+                title: Value(decryptedTitle),
+                body: Value(decryptedBody),
+                createdAt: Value(noteResponse.updatedAt),
+                updatedAt: Value(noteResponse.updatedAt),
+                sortIndex: Value(noteResponse.position),
+                serverVersion: Value(noteResponse.serverVersion),
+                isDeleted: Value(noteResponse.isDeleted),
+                categoryId: Value(noteResponse.categoryId),
+              ),
+            );
+      }
+    }
+  }
+
+  Future<List<Note>> _loadNotesFromDatabase() async {
+    final List<DbNote> rows = await _database.getAllNotes();
+    return rows.map(_fromDbNote).toList();
+  }
+
+  Note _fromDbNote(DbNote row) {
     return Note(
       id: row.id,
+      uuid: row.uuid,
       title: row.title,
       body: row.body,
       createdAt: row.createdAt,
       updatedAt: row.updatedAt,
       index: row.sortIndex,
+      serverVersion: row.serverVersion,
+      isDeleted: row.isDeleted,
+      categoryId: row.categoryId,
+    );
+  }
+
+  Category _fromDbCategory(DbCategory row) {
+    return Category(
+      uuid: row.uuid,
+      encryptedName: row.encryptedName,
+      serverVersion: row.serverVersion,
+      isDeleted: row.isDeleted,
+      updatedAt: row.updatedAt,
     );
   }
 }

lib/data/sync_models.dart

@@ -0,0 +1,258 @@
+import 'package:notas/models/note.dart';
+import 'package:notas/models/category.dart';
+
+// DTOs para sincronización con el servidor
+
+class SyncRequest {
+  SyncRequest({
+    DateTime? lastSyncAt,
+    required this.changes,
+  }) : lastSyncAt = lastSyncAt ?? DateTime.utc(1970, 1, 1);
+
+  final DateTime lastSyncAt;
+  final SyncChanges changes;
+
+  Map<String, dynamic> toJson() {
+    return {
+      'lastSyncAt': lastSyncAt.toIso8601String(),
+      'changes': changes.toJson(),
+    };
+  }
+}
+
+class SyncChanges {
+  const SyncChanges({
+    this.categories = const [],
+    this.notes = const [],
+  });
+
+  final List<SyncCategoryPayload> categories;
+  final List<SyncNotePayload> notes;
+
+  Map<String, dynamic> toJson() {
+    return {
+      if (categories.isNotEmpty)
+        'categories': categories.map((c) => c.toJson()).toList(),
+      if (notes.isNotEmpty)
+        'notes': notes.map((n) => n.toJson()).toList(),
+    };
+  }
+}
+
+class SyncChangesResponse {
+  const SyncChangesResponse({
+    this.categories = const [],
+    this.notes = const [],
+  });
+
+  final List<SyncCategoryResponse> categories;
+  final List<SyncNoteResponse> notes;
+
+  factory SyncChangesResponse.fromJson(Map<String, dynamic> json) {
+    final List<dynamic> categoriesJson = json['categories'] as List<dynamic>? ?? [];
+    final List<dynamic> notesJson = json['notes'] as List<dynamic>? ?? [];
+
+    return SyncChangesResponse(
+      categories: categoriesJson
+          .map((c) => SyncCategoryResponse.fromJson(c as Map<String, dynamic>))
+          .toList(),
+      notes: notesJson
+          .map((n) => SyncNoteResponse.fromJson(n as Map<String, dynamic>))
+          .toList(),
+    );
+  }
+}
+class SyncCategoryPayload {
+  const SyncCategoryPayload({
+    required this.id,
+    required this.encryptedName,
+    required this.serverVersion,
+    this.isDeleted = false,
+    required this.updatedAt,
+  });
+
+  final String id; // uuid
+  final String encryptedName;
+  final int serverVersion;
+  final bool isDeleted;
+  final DateTime updatedAt;
+
+  factory SyncCategoryPayload.fromCategory(Category category) {
+    return SyncCategoryPayload(
+      id: category.uuid,
+      encryptedName: category.encryptedName,
+      serverVersion: category.serverVersion,
+      isDeleted: category.isDeleted,
+      updatedAt: category.updatedAt,
+    );
+  }
+
+  Map<String, dynamic> toJson() {
+    return {
+      'id': id,
+      'encrypted_name': encryptedName,
+      'serverVersion': serverVersion,
+      'isDeleted': isDeleted,
+      'updatedAt': updatedAt.toIso8601String(),
+    };
+  }
+}
+
+class SyncNotePayload {
+  const SyncNotePayload({
+    required this.id,
+    this.categoryId,
+    required this.encryptedTitle,
+    required this.encryptedBody,
+    required this.serverVersion,
+    this.position = 0,
+    this.isDeleted = false,
+    required this.updatedAt,
+  });
+
+  final String id; // uuid
+  final String? categoryId;
+  final String encryptedTitle;
+  final String encryptedBody;
+  final int serverVersion;
+  final int position;
+  final bool isDeleted;
+  final DateTime updatedAt;
+
+  factory SyncNotePayload.fromNote(
+    Note note, {
+    required String encryptedTitle,
+    required String encryptedBody,
+  }) {
+    return SyncNotePayload(
+      id: note.uuid,
+      categoryId: note.categoryId,
+      encryptedTitle: encryptedTitle,
+      encryptedBody: encryptedBody,
+      serverVersion: note.serverVersion,
+      position: note.index,
+      isDeleted: note.isDeleted,
+      updatedAt: note.updatedAt,
+    );
+  }
+
+  Map<String, dynamic> toJson() {
+    return {
+      'id': id,
+      if (categoryId != null) 'categoryId': categoryId,
+      'encrypted_title': encryptedTitle,
+      'encrypted_body': encryptedBody,
+      'serverVersion': serverVersion,
+      if (position != 0) 'position': position,
+      if (isDeleted) 'isDeleted': isDeleted,
+      'updatedAt': updatedAt.toIso8601String(),
+    };
+  }
+}
+
+class SyncResponse {
+  const SyncResponse({
+    required this.serverTimestamp,
+    required this.synced,
+    required this.changes,
+  });
+
+  final DateTime serverTimestamp;
+  final bool synced;
+  final SyncChangesResponse changes;
+
+  factory SyncResponse.fromJson(Map<String, dynamic> json) {
+    return SyncResponse(
+      serverTimestamp:
+          DateTime.parse(json['serverTimestamp'] as String),
+      synced: json['synced'] as bool? ?? false,
+        changes: SyncChangesResponse.fromJson(
+          json['changes'] as Map<String, dynamic>? ?? {}),
+    );
+  }
+}
+
+class SyncCategoryResponse {
+  const SyncCategoryResponse({
+    required this.id,
+    required this.encryptedName,
+    required this.serverVersion,
+    this.isDeleted = false,
+    required this.updatedAt,
+  });
+
+  final String id; // uuid
+  final String encryptedName;
+  final int serverVersion;
+  final bool isDeleted;
+  final DateTime updatedAt;
+
+  factory SyncCategoryResponse.fromJson(Map<String, dynamic> json) {
+    return SyncCategoryResponse(
+      id: json['id'] as String,
+      encryptedName: json['encrypted_name'] as String,
+      serverVersion: json['serverVersion'] as int,
+      isDeleted: json['isDeleted'] as bool? ?? false,
+      updatedAt: DateTime.parse(json['updatedAt'] as String),
+    );
+  }
+
+  Category toCategory() {
+    return Category(
+      uuid: id,
+      encryptedName: encryptedName,
+      serverVersion: serverVersion,
+      isDeleted: isDeleted,
+      updatedAt: updatedAt,
+    );
+  }
+}
+
+class SyncNoteResponse {
+  const SyncNoteResponse({
+    required this.id,
+    this.categoryId,
+    required this.encryptedTitle,
+    required this.encryptedBody,
+    required this.serverVersion,
+    this.position = 0,
+    this.isDeleted = false,
+    required this.updatedAt,
+  });
+
+  final String id; // uuid
+  final String? categoryId;
+  final String encryptedTitle;
+  final String encryptedBody;
+  final int serverVersion;
+  final int position;
+  final bool isDeleted;
+  final DateTime updatedAt;
+
+  factory SyncNoteResponse.fromJson(Map<String, dynamic> json) {
+    return SyncNoteResponse(
+      id: json['id'] as String,
+      categoryId: json['categoryId'] as String?,
+      encryptedTitle: json['encrypted_title'] as String,
+      encryptedBody: json['encrypted_body'] as String,
+      serverVersion: json['serverVersion'] as int,
+      position: json['position'] as int? ?? 0,
+      isDeleted: json['isDeleted'] as bool? ?? false,
+      updatedAt: DateTime.parse(json['updatedAt'] as String),
+    );
+  }
+
+  Note toNote() {
+    return Note(
+      uuid: id,
+      title: 'Encrypted', // placeholder, será descifrado por la app
+      body: 'Encrypted', // placeholder, será descifrado por la app
+      createdAt: updatedAt,
+      updatedAt: updatedAt,
+      index: position,
+      serverVersion: serverVersion,
+      isDeleted: isDeleted,
+      categoryId: categoryId,
+    );
+  }
+}

lib/models/category.dart

@@ -0,0 +1,45 @@
+import 'package:uuid/uuid.dart';
+
+class Category {
+  Category({
+    String? uuid,
+    required this.encryptedName,
+    this.serverVersion = 0,
+    this.isDeleted = false,
+    required this.updatedAt,
+  }) : uuid = uuid ?? Uuid().v4();
+
+  final String uuid;
+  final String encryptedName;
+  final int serverVersion;
+  final bool isDeleted;
+  final DateTime updatedAt;
+
+  Category copyWith({
+    String? uuid,
+    String? encryptedName,
+    int? serverVersion,
+    bool? isDeleted,
+    DateTime? updatedAt,
+  }) {
+    return Category(
+      uuid: uuid ?? this.uuid,
+      encryptedName: encryptedName ?? this.encryptedName,
+      serverVersion: serverVersion ?? this.serverVersion,
+      isDeleted: isDeleted ?? this.isDeleted,
+      updatedAt: updatedAt ?? this.updatedAt,
+    );
+  }
+
+  @override
+  bool operator ==(Object other) {
+    if (identical(this, other)) {
+      return true;
+    }
+
+    return other is Category && uuid == other.uuid;
+  }
+
+  @override
+  int get hashCode => uuid.hashCode;
+}

lib/models/note.dart

@@ -1,39 +1,60 @@
+import 'package:uuid/uuid.dart';
+
 // Model: Note
 // - Representa una nota guardada en la app.
-// - `id` viene de SQLite y sirve como identificador estable.
+// - `id` es el identificador local de SQLite (autoincrement).
+// - `uuid` es el identificador global sincronizado con el servidor.
 // - `index` representa el orden visual dentro de la lista.
+// - `serverVersion` se usa para resolver conflictos en sync.
+// - `isDeleted` marca eliminaciones blandas.
 class Note {
-  const Note({
+  Note({
     this.id,
+    String? uuid,
     required this.title,
     required this.body,
     required this.createdAt,
     required this.updatedAt,
     required this.index,
-  });
+    this.serverVersion = 0,
+    this.isDeleted = false,
+    this.categoryId,
+  }) : uuid = uuid ?? Uuid().v4();
 
   final int? id;
+  final String uuid;
   final String title;
   final String body;
   final DateTime createdAt;
   final DateTime updatedAt;
   final int index;
+  final int serverVersion;
+  final bool isDeleted;
+  final String? categoryId;
 
   Note copyWith({
     int? id,
+    String? uuid,
     String? title,
     String? body,
     DateTime? createdAt,
     DateTime? updatedAt,
     int? index,
+    int? serverVersion,
+    bool? isDeleted,
+    String? categoryId,
   }) {
     return Note(
       id: id ?? this.id,
+      uuid: uuid ?? this.uuid,
       title: title ?? this.title,
       body: body ?? this.body,
       createdAt: createdAt ?? this.createdAt,
       updatedAt: updatedAt ?? this.updatedAt,
       index: index ?? this.index,
+      serverVersion: serverVersion ?? this.serverVersion,
+      isDeleted: isDeleted ?? this.isDeleted,
+      categoryId: categoryId ?? this.categoryId,
     );
   }
 
@@ -43,9 +64,9 @@ class Note {
       return true;
     }
 
-    return other is Note && id != null && other.id == id;
+    return other is Note && uuid == other.uuid;
   }
 
   @override
-  int get hashCode => id?.hashCode ?? Object.hash(title, body, createdAt, updatedAt, index);
+  int get hashCode => uuid.hashCode;
 }

lib/screens/home_screen.dart

@@ -75,6 +75,12 @@ class _HomeScreenState extends State<HomeScreen> {
       setState(() {
         _notes = updatedNotes;
       });
+
+      // Trigger sync after creating a note and refresh local list
+      try {
+        await widget.repository.performSync();
+        await _loadNotes();
+      } catch (_) {}
     }
   }
 
@@ -92,6 +98,12 @@ class _HomeScreenState extends State<HomeScreen> {
     setState(() {
       _notes = updatedNotes;
     });
+
+    // Trigger sync after deleting a note and refresh local list
+    try {
+      await widget.repository.performSync();
+      await _loadNotes();
+    } catch (_) {}
   }
 
   Future<void> _reorderNote(int oldIndex, int newIndex) async {
@@ -140,6 +152,11 @@ class _HomeScreenState extends State<HomeScreen> {
         setState(() {
           _notes = _normalizeNotes(updatedNotes);
         });
+        // Trigger sync after editing a note and refresh local list
+        try {
+          await widget.repository.performSync();
+          await _loadNotes();
+        } catch (_) {}
       }
     }
   }
@@ -172,9 +189,16 @@ class _HomeScreenState extends State<HomeScreen> {
         ? const Center(child: CircularProgressIndicator())
         : _notes.isEmpty
             ? const _EmptyState()
-            : MouseRegion(
+            : RefreshIndicator(
-                cursor: _isDragging ? SystemMouseCursors.grabbing : SystemMouseCursors.basic,
+                onRefresh: () async {
-                child: MasonryGridView.count(
+                  try {
+                    await widget.repository.performSync();
+                  } catch (_) {}
+                  await _loadNotes();
+                },
+                child: MouseRegion(
+                  cursor: _isDragging ? SystemMouseCursors.grabbing : SystemMouseCursors.basic,
+                  child: MasonryGridView.count(
                   crossAxisCount: crossAxisCount,
                   mainAxisSpacing: 10,
                   crossAxisSpacing: 10,
@@ -296,7 +320,8 @@ class _HomeScreenState extends State<HomeScreen> {
                     );
                   },
                 ),
-              );
+              ),
+            );
 
     return Scaffold(
       body: Container(

lib/screens/settings_screen.dart

@@ -1,5 +1,7 @@
 import 'package:flutter/material.dart';
+import 'package:notas/data/local_vault_service.dart';
 import 'package:notas/widgets/search_app_bar.dart';
+import 'package:notas/data/api_client.dart';
 
 class SettingsScreen extends StatefulWidget {
   const SettingsScreen({
@@ -17,6 +19,11 @@ class SettingsScreen extends StatefulWidget {
 
 class _SettingsScreenState extends State<SettingsScreen> {
   bool _isBusy = false;
+  final TextEditingController _endpointController = TextEditingController();
+  final TextEditingController _encryptionKeyController = TextEditingController();
+  bool _endpointLoading = true;
+  bool _encryptionKeyLoading = false;
+  bool _encryptionKeyVisible = false;
 
   Future<void> _confirmAndDeleteAll() async {
     final bool? confirmed = await showDialog<bool>(
@@ -59,6 +66,91 @@ class _SettingsScreenState extends State<SettingsScreen> {
   }
 
   @override
+  void initState() {
+    super.initState();
+    _loadEndpoint();
+  }
+
+  Future<void> _loadEndpoint() async {
+    final String endpoint = await ApiConfig.getEndpoint();
+    if (!mounted) return;
+    _endpointController.text = endpoint;
+    setState(() {
+      _endpointLoading = false;
+    });
+  }
+
+  Future<void> _loadEncryptionKey() async {
+    setState(() {
+      _encryptionKeyLoading = true;
+    });
+
+    try {
+      final String? encryptionKey = await LocalVaultService.instance.readEncryptionKey();
+
+      if (!mounted) return;
+
+      if (encryptionKey == null || encryptionKey.isEmpty) {
+        _encryptionKeyController.text = '';
+        _encryptionKeyVisible = false;
+        ScaffoldMessenger.of(context).showSnackBar(
+          const SnackBar(content: Text('No se pudo leer la clave de cifrado.')),
+        );
+        return;
+      }
+
+      _encryptionKeyController.text = encryptionKey;
+      _encryptionKeyVisible = true;
+      ScaffoldMessenger.of(context).showSnackBar(
+        const SnackBar(content: Text('Clave de cifrado mostrada.')),
+      );
+    } catch (error) {
+      if (!mounted) return;
+      ScaffoldMessenger.of(context).showSnackBar(
+        SnackBar(content: Text('Error al leer la clave de cifrado: $error')),
+      );
+    } finally {
+      if (mounted) {
+        setState(() {
+          _encryptionKeyLoading = false;
+        });
+      }
+    }
+  }
+
+  void _hideEncryptionKey() {
+    setState(() {
+      _encryptionKeyVisible = false;
+      _encryptionKeyController.clear();
+    });
+  }
+
+  @override
+  void dispose() {
+    _endpointController.dispose();
+    _encryptionKeyController.dispose();
+    super.dispose();
+  }
+
+  Future<void> _saveEndpoint() async {
+    final String value = _endpointController.text.trim();
+    try {
+      await ApiConfig.setEndpoint(value);
+      if (!mounted) return;
+      ScaffoldMessenger.of(context).showSnackBar(const SnackBar(content: Text('Endpoint guardado')));
+    } catch (e) {
+      if (!mounted) return;
+      ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text('Error guardando endpoint: $e')));
+    }
+  }
+
+  Future<void> _resetEndpoint() async {
+    await ApiConfig.clearEndpoint();
+    final String endpoint = await ApiConfig.getEndpoint();
+    if (!mounted) return;
+    _endpointController.text = endpoint;
+    ScaffoldMessenger.of(context).showSnackBar(const SnackBar(content: Text('Endpoint restaurado al valor por defecto')));
+  }
   Widget build(BuildContext context) {
     return Scaffold(
       body: Container(
@@ -97,6 +189,113 @@ class _SettingsScreenState extends State<SettingsScreen> {
                       ),
                       const SizedBox(height: 16),
                       const Text('Esto cerrará el vault actual y eliminará la base de datos local junto con la clave de cifrado.'),
+                      const SizedBox(height: 24),
+                      const Text('API endpoint (ej: http://localhost:3000/api)'),
+                      const SizedBox(height: 8),
+                      Row(
+                        crossAxisAlignment: CrossAxisAlignment.start,
+                        children: [
+                          Expanded(
+                            child: _endpointLoading
+                                ? const SizedBox(height: 48, child: Center(child: CircularProgressIndicator()))
+                                : TextField(
+                                    controller: _endpointController,
+                                    style: const TextStyle(color: Colors.white),
+                                    keyboardType: TextInputType.url,
+                                    decoration: InputDecoration(
+                                      labelText: 'API endpoint',
+                                      labelStyle: TextStyle(color: Colors.white.withValues(alpha: 0.7)),
+                                      filled: true,
+                                      fillColor: Colors.white.withValues(alpha: 0.05),
+                                      border: OutlineInputBorder(
+                                        borderRadius: BorderRadius.circular(14),
+                                        borderSide: BorderSide(color: Colors.white.withValues(alpha: 0.12)),
+                                      ),
+                                      enabledBorder: OutlineInputBorder(
+                                        borderRadius: BorderRadius.circular(14),
+                                        borderSide: BorderSide(color: Colors.white.withValues(alpha: 0.12)),
+                                      ),
+                                      focusedBorder: OutlineInputBorder(
+                                        borderRadius: BorderRadius.circular(14),
+                                        borderSide: const BorderSide(color: Colors.amber, width: 1.2),
+                                      ),
+                                    ),
+                                  ),
+                          ),
+                          const SizedBox(width: 8),
+                          Column(
+                            mainAxisSize: MainAxisSize.min,
+                            children: [
+                              ElevatedButton(
+                                onPressed: _endpointLoading ? null : _saveEndpoint,
+                                child: const Text('Guardar'),
+                              ),
+                              const SizedBox(height: 8),
+                              OutlinedButton(
+                                onPressed: _endpointLoading ? null : _resetEndpoint,
+                                child: const Text('Restaurar'),
+                              ),
+                            ],
+                          ),
+                        ],
+                      ),
+                      const SizedBox(height: 24),
+                      const Text('Clave de cifrado local'),
+                      const SizedBox(height: 8),
+                      Row(
+                        crossAxisAlignment: CrossAxisAlignment.start,
+                        children: [
+                          Expanded(
+                            child: TextField(
+                              controller: _encryptionKeyController,
+                              readOnly: true,
+                              obscureText: !_encryptionKeyVisible,
+                              enableSuggestions: false,
+                              autocorrect: false,
+                              style: const TextStyle(color: Colors.white),
+                              decoration: InputDecoration(
+                                labelText: _encryptionKeyVisible ? 'Clave de cifrado' : 'Oculta hasta pulsar mostrar',
+                                labelStyle: TextStyle(color: Colors.white.withValues(alpha: 0.7)),
+                                filled: true,
+                                fillColor: Colors.white.withValues(alpha: 0.05),
+                                border: OutlineInputBorder(
+                                  borderRadius: BorderRadius.circular(14),
+                                  borderSide: BorderSide(color: Colors.white.withValues(alpha: 0.12)),
+                                ),
+                                enabledBorder: OutlineInputBorder(
+                                  borderRadius: BorderRadius.circular(14),
+                                  borderSide: BorderSide(color: Colors.white.withValues(alpha: 0.12)),
+                                ),
+                                focusedBorder: OutlineInputBorder(
+                                  borderRadius: BorderRadius.circular(14),
+                                  borderSide: const BorderSide(color: Colors.amber, width: 1.2),
+                                ),
+                              ),
+                            ),
+                          ),
+                          const SizedBox(width: 8),
+                          Column(
+                            mainAxisSize: MainAxisSize.min,
+                            children: [
+                              ElevatedButton(
+                                onPressed: _encryptionKeyLoading ? null : _loadEncryptionKey,
+                                child: _encryptionKeyLoading
+                                    ? const SizedBox(
+                                        width: 16,
+                                        height: 16,
+                                        child: CircularProgressIndicator(strokeWidth: 2),
+                                      )
+                                    : const Text('Mostrar'),
+                              ),
+                              const SizedBox(height: 8),
+                              OutlinedButton(
+                                onPressed: _encryptionKeyVisible ? _hideEncryptionKey : null,
+                                child: const Text('Ocultar'),
+                              ),
+                            ],
+                          ),
+                        ],
+                      ),
                     ],
                   ),
                 ),

lib/screens/vault_access_screen.dart

@@ -1,5 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:notas/widgets/app_title_bar.dart';
+import 'package:notas/data/api_client.dart';
 
 class VaultAccessScreen extends StatefulWidget {
   const VaultAccessScreen({
@@ -22,6 +23,29 @@ class VaultAccessScreen extends StatefulWidget {
 class _VaultAccessScreenState extends State<VaultAccessScreen> {
   final TextEditingController _emailController = TextEditingController();
   final TextEditingController _passwordController = TextEditingController();
+  final TextEditingController _endpointController = TextEditingController();
+  bool _endpointLoading = true;
+
+  @override
+  void initState() {
+    super.initState();
+    _loadEndpoint();
+  }
+
+  Future<void> _loadEndpoint() async {
+    final String endpoint = await ApiConfig.getEndpoint();
+    if (!mounted) return;
+    _endpointController.text = endpoint;
+    setState(() {
+      _endpointLoading = false;
+    });
+  }
+
+  Future<void> _persistEndpointFromField() async {
+    final String value = _endpointController.text.trim();
+    if (value.isEmpty) return;
+    await ApiConfig.setEndpoint(value);
+  }
 
   @override
   void dispose() {
@@ -31,6 +55,8 @@ class _VaultAccessScreenState extends State<VaultAccessScreen> {
   }
 
   Future<void> _handleCreateAccount() async {
+    await _persistEndpointFromField();
+
     await widget.onCreateAccountPressed(
       _emailController.text.trim(),
       _passwordController.text,
@@ -38,6 +64,8 @@ class _VaultAccessScreenState extends State<VaultAccessScreen> {
   }
 
   Future<void> _handleSignIn() async {
+    await _persistEndpointFromField();
+
     await widget.onSignInPressed(
       _emailController.text.trim(),
       _passwordController.text,
@@ -112,13 +140,43 @@ class _VaultAccessScreenState extends State<VaultAccessScreen> {
                               ),
                             ),
                             const SizedBox(height: 28),
+                            _endpointLoading
+                                ? const SizedBox(
+                                    height: 48,
+                                    child: Center(child: CircularProgressIndicator()),
+                                  )
+                                : TextField(
+                                    controller: _endpointController,
+                                    enabled: !widget.isBusy,
+                                    keyboardType: TextInputType.url,
+                                    style: const TextStyle(color: Colors.white),
+                                    decoration: InputDecoration(
+                                      labelText: 'API endpoint',
+                                      labelStyle: TextStyle(color: Colors.white.withValues(alpha: 0.7)),
+                                      filled: true,
+                                      fillColor: Colors.white.withValues(alpha: 0.05),
+                                      border: OutlineInputBorder(
+                                        borderRadius: BorderRadius.circular(14),
+                                        borderSide: BorderSide(color: Colors.white.withValues(alpha: 0.12)),
+                                      ),
+                                      enabledBorder: OutlineInputBorder(
+                                        borderRadius: BorderRadius.circular(14),
+                                        borderSide: BorderSide(color: Colors.white.withValues(alpha: 0.12)),
+                                      ),
+                                      focusedBorder: OutlineInputBorder(
+                                        borderRadius: BorderRadius.circular(14),
+                                        borderSide: const BorderSide(color: Colors.amber, width: 1.2),
+                                      ),
+                                    ),
+                                  ),
+                            const SizedBox(height: 16),
                             TextField(
                               controller: _emailController,
                               enabled: !widget.isBusy,
-                              keyboardType: TextInputType.emailAddress,
+                              keyboardType: TextInputType.text,
                               style: const TextStyle(color: Colors.white),
                               decoration: InputDecoration(
-                                labelText: 'Email',
+                                labelText: 'Usuario',
                                 labelStyle: TextStyle(color: Colors.white.withValues(alpha: 0.7)),
                                 filled: true,
                                 fillColor: Colors.white.withValues(alpha: 0.05),

lib/widgets/app_title_bar_io.dart

@@ -1,9 +1,17 @@
 import 'package:flutter/material.dart';
 import 'package:notas/platform/app_platform.dart';
+import 'package:notas/widgets/sync_status_indicator.dart';
 import 'package:window_manager/window_manager.dart';
 
 class AppTitleBar extends StatelessWidget {
-  const AppTitleBar({super.key});
+  const AppTitleBar({
+    this.syncStatus = SyncStatus.idle,
+    this.syncErrorMessage,
+    super.key,
+  });
+
+  final SyncStatus syncStatus;
+  final String? syncErrorMessage;
 
   @override
   Widget build(BuildContext context) {
@@ -12,33 +20,62 @@ class AppTitleBar extends StatelessWidget {
     }
 
     if (isMacOS) {
-      return const SizedBox(
+      return SizedBox(
         height: 28,
         child: Center(
-          child: Text(
+          child: Row(
-            'Mis Notas',
+            mainAxisAlignment: MainAxisAlignment.center,
-            style: TextStyle(color: Colors.white70, fontSize: 13),
+            children: [
+              const Text(
+                'Mis Notas',
+                style: TextStyle(color: Colors.white70, fontSize: 13),
+              ),
+              const SizedBox(width: 8),
+              SyncStatusIndicator(
+                status: syncStatus,
+                errorMessage: syncErrorMessage,
+              ),
+            ],
           ),
         ),
       );
     }
 
     if (isLinux) {
-      return const _KdeTitleBar();
+      return _KdeTitleBar(
+        syncStatus: syncStatus,
+        syncErrorMessage: syncErrorMessage,
+      );
     }
 
-    return const SizedBox(
+    return SizedBox(
       height: 40,
       child: WindowCaption(
         brightness: Brightness.dark,
-        title: Text('Mis Notas', style: TextStyle(color: Colors.white)),
+        title: Row(
+          mainAxisSize: MainAxisSize.min,
+          children: [
+            const Text('Mis Notas', style: TextStyle(color: Colors.white)),
+            const SizedBox(width: 8),
+            SyncStatusIndicator(
+              status: syncStatus,
+              errorMessage: syncErrorMessage,
+            ),
+          ],
+        ),
       ),
     );
   }
 }
 
 class _KdeTitleBar extends StatefulWidget {
-  const _KdeTitleBar();
+  const _KdeTitleBar({
+    this.syncStatus = SyncStatus.idle,
+    this.syncErrorMessage,
+  });
+
+  final SyncStatus syncStatus;
+  final String? syncErrorMessage;
 
   @override
   State<_KdeTitleBar> createState() => _KdeTitleBarState();
@@ -130,12 +167,33 @@ class _KdeTitleBarState extends State<_KdeTitleBar> with WindowListener {
             ),
             const IgnorePointer(
               child: Center(
-                child: Text(
+                child: Row(
-                  'Mis Notas',
+                  mainAxisAlignment: MainAxisAlignment.center,
-                  style: TextStyle(
+                  children: [
-                    color: Color.fromARGB(255, 163, 163, 163),
+                    Text(
-                    fontSize: 14,
+                      'Mis Notas',
-                    fontWeight: FontWeight.w500,
+                      style: TextStyle(
+                        color: Color.fromARGB(255, 163, 163, 163),
+                        fontSize: 14,
+                        fontWeight: FontWeight.w500,
+                      ),
+                    ),
+                  ],
+                ),
+              ),
+            ),
+            Positioned(
+              left: 0,
+              top: 0,
+              bottom: 0,
+              child: IgnorePointer(
+                child: Padding(
+                  padding: const EdgeInsets.symmetric(horizontal: 8),
+                  child: Center(
+                    child: SyncStatusIndicator(
+                      status: widget.syncStatus,
+                      errorMessage: widget.syncErrorMessage,
+                    ),
                   ),
                 ),
               ),

lib/widgets/app_title_bar_stub.dart

@@ -1,7 +1,15 @@
 import 'package:flutter/material.dart';
+import 'package:notas/widgets/sync_status_indicator.dart';
 
 class AppTitleBar extends StatelessWidget {
-  const AppTitleBar({super.key});
+  const AppTitleBar({
+    this.syncStatus = SyncStatus.idle,
+    this.syncErrorMessage,
+    super.key,
+  });
+
+  final SyncStatus syncStatus;
+  final String? syncErrorMessage;
 
   @override
   Widget build(BuildContext context) {

lib/widgets/sync_status_indicator.dart

@@ -0,0 +1,62 @@
+import 'package:flutter/material.dart';
+
+enum SyncStatus {
+  idle,
+  syncing,
+  synced,
+  error,
+}
+
+class SyncStatusIndicator extends StatelessWidget {
+  const SyncStatusIndicator({
+    required this.status,
+    this.errorMessage,
+    super.key,
+  });
+
+  final SyncStatus status;
+  final String? errorMessage;
+
+  @override
+  Widget build(BuildContext context) {
+    switch (status) {
+      case SyncStatus.idle:
+        return const SizedBox.shrink();
+
+      case SyncStatus.syncing:
+        return const Tooltip(
+          message: 'Sincronizando...',
+          child: SizedBox(
+            width: 16,
+            height: 16,
+            child: CircularProgressIndicator(
+              strokeWidth: 2,
+              valueColor: AlwaysStoppedAnimation<Color>(
+                Color.fromARGB(255, 150, 150, 150),
+              ),
+            ),
+          ),
+        );
+
+      case SyncStatus.synced:
+        return const Tooltip(
+          message: 'Sincronizado',
+          child: Icon(
+            Icons.check_circle,
+            size: 16,
+            color: Colors.green,
+          ),
+        );
+
+      case SyncStatus.error:
+        return Tooltip(
+          message: errorMessage ?? 'Error al sincronizar',
+          child: const Icon(
+            Icons.error,
+            size: 16,
+            color: Colors.red,
+          ),
+        );
+    }
+  }
+}

pubspec.lock

@@ -162,13 +162,21 @@ packages:
     source: hosted
     version: "3.1.2"
   crypto:
-    dependency: transitive
+    dependency: "direct main"
     description:
       name: crypto
       sha256: c8ea0233063ba03258fbcf2ca4d6dadfefe14f02fab57702265467a19f27fadf
       url: "https://pub.dev"
     source: hosted
     version: "3.0.7"
+  cryptography:
+    dependency: "direct main"
+    description:
+      name: cryptography
+      sha256: "3eda3029d34ec9095a27a198ac9785630fe525c0eb6a49f3d575272f8e792ef0"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.9.0"
   cupertino_icons:
     dependency: "direct main"
     description:
@@ -360,6 +368,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.0.3"
+  http:
+    dependency: "direct main"
+    description:
+      name: http
+      sha256: "5895291c13fa8a3bd82e76d5627f69e0d85ca6a30dcac95c4ea19a5d555879c2"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.13.6"
   http_multi_server:
     dependency: transitive
     description:
@@ -893,6 +909,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.4.0"
+  uuid:
+    dependency: "direct main"
+    description:
+      name: uuid
+      sha256: "1fef9e8e11e2991bb773070d4656b7bd5d850967a2456cfc83cf47925ba79489"
+      url: "https://pub.dev"
+    source: hosted
+    version: "4.5.3"
   vector_math:
     dependency: transitive
     description:

pubspec.yaml

@@ -44,6 +44,10 @@ dependencies:
   flutter_secure_storage: ^10.2.0
   local_auth: ^3.0.1
   sqlite3: ^3.3.1
+  http: ^0.13.6
+  crypto: ^3.0.6
+  cryptography: ^2.7.0
+  uuid: ^4.0.0
 
 dev_dependencies:
   flutter_test:
@@ -70,7 +74,7 @@ flutter:
   # the material Icons class.
   uses-material-design: true
 
-assets:
+  assets:
     - assets/icon.png
 
 hooks: