Preserve explicit model and provider architecture (#30)

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':