diff --git a/AGENTS.md b/AGENTS.md
index c1ed5ea..002a572 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -8,6 +8,24 @@
 - For cross-module work, apply every relevant scoped instruction file and
   completion workflow.
 
+## Data and state architecture
+
+Preserve explicit **DTO → mapper → service → data model → provider → UI**
+boundaries across the project. This is a standing requirement for application
+features, shared packages, stub services and future mobile clients.
+
+- DTOs describe transport data; mappers convert it to/from domain data models.
+- Services own external I/O and use mappers. Service contracts return data models,
+  never transport DTOs or untyped response maps to the UI.
+- Data models remain distinct from provider state and transport serialization.
+- Providers sit on top of services, coordinating loading, errors and state and
+  exposing models to the UI. Widgets render models and invoke provider actions.
+- Keep reusable domain models, services and providers in shared packages; clients
+  compose them rather than copy business logic or create alternate data paths.
+- Preserve these boundaries when replacing stubs with real backend adapters.
+  Review every changed feature against them before delivery. Apply the detailed
+  frontend requirements in `frontend/AGENTS.md` to all Flutter clients/packages.
+
 ## UX
 
 For any user-facing interface work, follow the
diff --git a/README.md b/README.md
index da77542..232dcb1 100644
--- a/README.md
+++ b/README.md
@@ -160,6 +160,16 @@ Before backend integration, agree on the customer, KYC, eligibility/limits and
 customer-scoped payment contracts for one complete transaction flow. These are
 intended boundaries, not claims that the required operations already exist.
 
+## Client architecture
+
+Keep **DTO → mapper → service → data model → provider → UI** boundaries in every
+feature and shared package. Services return mapped domain models; providers sit
+on services and expose loading/error/data state. Widgets render models and call
+provider actions. DTO serialization and backend calls belong below this boundary.
+Shared packages own reusable domain logic for web and mobile; stub replacements
+must preserve the same contracts. See the standing rules in `AGENTS.md` and
+`frontend/AGENTS.md`.
+
 ## Contribution workflow
 
 Follow [`AGENTS.md`](AGENTS.md) and the applicable scoped guidelines, including
diff --git a/docs/implementation.md b/docs/implementation.md
index c7a539c..9eab2b1 100644
--- a/docs/implementation.md
+++ b/docs/implementation.md
@@ -256,3 +256,26 @@ Validation: all 115 frontend tests, app analysis, app Dart formatting, web build
 and diff checks pass. Updated existing copy expectations; telemetry tests still
 verify simulated events never count as real business success. No new click events
 were needed for this presentation-only cleanup.
+
+## Data model and provider boundaries — task #30
+
+- `architecture-30`, based on workspace PR #29. Root and frontend agent rules,
+  plus README, now explicitly preserve DTO → mapper → service → data model →
+  provider → UI across app features, shared packages, stubs and future clients.
+  Models cannot be replaced by providers or reused as transport DTOs merely
+  because their fields currently match.
+- Checked application service access: widgets compose providers with service
+  dependencies; they do not parse DTOs or invoke backend operations directly.
+  KYC and wallet transaction services already map transport data to models.
+  Auth success responses now pass through explicit response DTOs and mappers;
+  wallet profile conversion now accepts a ProfileDTO instead of a raw string.
+- Existing models, provider state, asynchronous/error behavior and public service
+  contracts are preserved. DTOs/mappers remain service implementation details.
+  No UI, telemetry semantics or backend integration changed.
+- Frontend review and validation: formatting of all 6 changed Dart files passed;
+  analysis of sxchnge_auth and sxchnge_wallet passed; all 115 frontend tests
+  passed; diff check passed. Existing service, provider and integrated tests
+  exercise the mapping paths. No additional behavioral test was needed for these
+  direct field projections. No security scan requested.
+- Stack order: KYC #21 → limits #23 → workspace #29 → this contribution;
+  retarget each dependent PR to main after its base is merged.
diff --git a/frontend/AGENTS.md b/frontend/AGENTS.md
index 78530b8..6111d07 100644
--- a/frontend/AGENTS.md
+++ b/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.
diff --git a/frontend/packages/sxchnge_auth/lib/src/dto/results.dart b/frontend/packages/sxchnge_auth/lib/src/dto/results.dart
new file mode 100644
index 0000000..79b6dd0
--- /dev/null
+++ b/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;
+}
diff --git a/frontend/packages/sxchnge_auth/lib/src/mappers/results.dart b/frontend/packages/sxchnge_auth/lib/src/mappers/results.dart
new file mode 100644
index 0000000..b1456b1
--- /dev/null
+++ b/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);
+}
diff --git a/frontend/packages/sxchnge_auth/lib/src/services/dummy.dart b/frontend/packages/sxchnge_auth/lib/src/services/dummy.dart
index 2076781..28ba934 100644
--- a/frontend/packages/sxchnge_auth/lib/src/services/dummy.dart
+++ b/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),
+    );
   }
 }
diff --git a/frontend/packages/sxchnge_auth/lib/src/services/verification.dart b/frontend/packages/sxchnge_auth/lib/src/services/verification.dart
index 275e0e7..9ce505e 100644
--- a/frontend/packages/sxchnge_auth/lib/src/services/verification.dart
+++ b/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':
diff --git a/frontend/packages/sxchnge_wallet/lib/src/services/dummy.dart b/frontend/packages/sxchnge_wallet/lib/src/services/dummy.dart
index ec8cde2..8488fb5 100644
--- a/frontend/packages/sxchnge_wallet/lib/src/services/dummy.dart
+++ b/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.
diff --git a/frontend/packages/sxchnge_wallet/lib/src/transport/wallet.dart b/frontend/packages/sxchnge_wallet/lib/src/transport/wallet.dart
index 2614608..445b496 100644
--- a/frontend/packages/sxchnge_wallet/lib/src/transport/wallet.dart
+++ b/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);
 }