Preserve explicit model and provider architecture (#30)

frontend/AGENTS.md

@@ -12,6 +12,13 @@ skill to perform this completion workflow.
 
 ## Preserve the frontend architecture
 
+This applies to `frontend/app`, every shared package and future web/mobile
+clients, including in-memory stubs. Keep an explicit data model even when it
+currently resembles the DTO; do not use a provider as a substitute for that model.
+The UI depends on providers/models; providers depend on service contracts; service
+implementations own DTO conversion through mappers. Replacing a service must not
+require DTO or networking changes in widgets or providers.
+
 - Strictly preserve the existing `dto` -> `mapper` -> `service` -> `model` ->
   `provider` flow. Widgets consume models and provider state; they must not
   bypass the flow by parsing transport data or calling backend APIs directly.

frontend/packages/sxchnge_auth/lib/src/dto/results.dart

@@ -0,0 +1,11 @@
+/// Stub response contracts, replaced by generated transport types at integration.
+class AuthDTO {
+  const AuthDTO({required this.userId, required this.simulated});
+  final String userId;
+  final bool simulated;
+}
+
+class VerificationDTO {
+  const VerificationDTO({required this.simulated});
+  final bool simulated;
+}

frontend/packages/sxchnge_auth/lib/src/mappers/results.dart

@@ -0,0 +1,13 @@
+import '../dto/results.dart';
+import '../models/auth.dart';
+import '../models/verification.dart';
+
+abstract final class AuthMapper {
+  static AuthResult fromDTO(AuthDTO dto) =>
+      AuthResult(userId: dto.userId, isSimulated: dto.simulated);
+}
+
+abstract final class VerificationMapper {
+  static VerificationResult fromDTO(VerificationDTO dto) =>
+      VerificationResult(isSimulated: dto.simulated);
+}

frontend/packages/sxchnge_auth/lib/src/services/dummy.dart

@@ -1,3 +1,5 @@
+import '../dto/results.dart';
+import '../mappers/results.dart';
 import '../models/auth.dart';
 import 'contracts.dart';
 import 'verification.dart';
@@ -18,7 +20,9 @@ class DummyLoginService implements LoginService, SimulationInfo {
   Future<AuthResult> login(LoginRequest request) async {
     await Future<void>.delayed(delay);
     if (failure case final error?) throw AuthException(error);
-    return const AuthResult(userId: 'demo-user', isSimulated: true);
+    return AuthMapper.fromDTO(
+      const AuthDTO(userId: 'demo-user', simulated: true),
+    );
   }
 }
 
@@ -36,6 +40,8 @@ class DummySignupService implements SignupService, SimulationInfo {
   Future<AuthResult> signup(SignupRequest request) async {
     await Future<void>.delayed(delay);
     if (failure case final error?) throw AuthException(error);
-    return const AuthResult(userId: 'demo-user', isSimulated: true);
+    return AuthMapper.fromDTO(
+      const AuthDTO(userId: 'demo-user', simulated: true),
+    );
   }
 }

frontend/packages/sxchnge_auth/lib/src/services/verification.dart

@@ -1,3 +1,5 @@
+import '../dto/results.dart';
+import '../mappers/results.dart';
 import '../models/verification.dart';
 
 abstract interface class SimulationInfo {
@@ -30,7 +32,7 @@ class DummyVerificationService implements VerificationService, SimulationInfo {
   }) async {
     await Future<void>.delayed(delay);
     if (sendFailure case final error?) throw VerificationException(error);
-    return const VerificationResult(isSimulated: true);
+    return VerificationMapper.fromDTO(const VerificationDTO(simulated: true));
   }
 
   @override
@@ -38,7 +40,9 @@ class DummyVerificationService implements VerificationService, SimulationInfo {
     await Future<void>.delayed(delay);
     switch (token) {
       case 'demo-valid':
-        return const VerificationResult(isSimulated: true);
+        return VerificationMapper.fromDTO(
+          const VerificationDTO(simulated: true),
+        );
       case 'demo-expired':
         throw const VerificationException(VerificationError.expired);
       case 'demo-internal':

frontend/packages/sxchnge_wallet/lib/src/services/dummy.dart

@@ -204,7 +204,7 @@ class DummyWalletService implements WalletService {
   @override
   Future<AccountProfile> profile() async {
     await _wait();
-    return WalletMapper.profile(_locale);
+    return WalletMapper.profile(ProfileDTO(_locale));
   }
 
   @override
@@ -213,7 +213,7 @@ class DummyWalletService implements WalletService {
     if (!['en', 'ru'].contains(locale))
       throw const WalletException(WalletError.unsupported);
     _locale = locale;
-    return WalletMapper.profile(_locale);
+    return WalletMapper.profile(ProfileDTO(_locale));
   }
 
   // Kept separate from wallet fetch because LimitsService has a different result.

frontend/packages/sxchnge_wallet/lib/src/transport/wallet.dart

@@ -53,6 +53,11 @@ class OperationDTO {
   final bool fail;
 }
 
+class ProfileDTO {
+  const ProfileDTO(this.locale);
+  final String locale;
+}
+
 abstract final class WalletMapper {
   static CurrencyAccount account(AccountDTO d) => CurrencyAccount(
     id: d.id,
@@ -85,5 +90,5 @@ abstract final class WalletMapper {
     status: OperationStatus.values.byName(d.status),
     createdAt: d.created,
   );
-  static AccountProfile profile(String locale) => AccountProfile(locale);
+  static AccountProfile profile(ProfileDTO dto) => AccountProfile(dto.locale);
 }