Build exchange workspace and shared transaction services (#28)

frontend/packages/sxchnge_analytics/lib/sxchnge_analytics.dart

@@ -2,7 +2,7 @@ import 'dart:async';
 import 'dart:collection';
 import 'dart:math';
 
-enum JourneyKind { login, signup, verification, kyc }
+enum JourneyKind { login, signup, verification, kyc, topUp, exchange, payout }
 
 enum JourneyStep {
   login,
@@ -14,6 +14,10 @@ enum JourneyStep {
   kycSelfie,
   kycSubmission,
   kycStatus,
+  transferDraft,
+  transferQuote,
+  transferSubmission,
+  settlement,
 }
 
 enum JourneySignal {
@@ -27,6 +31,9 @@ enum JourneySignal {
 }
 
 enum JourneyFailure {
+  insufficientFunds,
+  limitExceeded,
+  declined,
   document,
   invalidCredentials,
   emailInUse,
@@ -79,7 +86,13 @@ class AnalyticsEvent {
   final bool simulated;
   final DateTime occurredAt;
   String get name {
-    final area = kind == JourneyKind.kyc ? 'kyc' : 'auth';
+    final area = switch (kind) {
+      JourneyKind.kyc => 'kyc',
+      JourneyKind.topUp => 'top_up',
+      JourneyKind.exchange => 'exchange',
+      JourneyKind.payout => 'payout',
+      _ => 'auth',
+    };
     var stage = step == null ? 'journey' : _snake(step!.name);
     if (kind == JourneyKind.kyc) stage = stage.replaceFirst('kyc_', '');
     return '${area}_${stage}_${signal.name}';
@@ -189,7 +202,7 @@ class JourneyRecorder {
     operation._finished = true;
     journey.pending--;
     journey.simulated |= simulated;
-    final complete = failure == null && !cancelled && terminal;
+    final complete = !cancelled && terminal;
     _emit(
       journey,
       cancelled
@@ -257,8 +270,8 @@ class JourneyRecorder {
     );
   }
 
-  void dispose() {
-    abandon(JourneyExit.disposed);
+  void dispose({bool abandonActive = true}) {
+    if (abandonActive) abandon(JourneyExit.disposed);
     _disposed = true;
     _idle?.cancel();
   }

frontend/packages/sxchnge_kyc/lib/limits_transport.dart

@@ -0,0 +1,2 @@
+/// Shared limit transport contract for service adapters.
+export 'src/transport/contracts.dart' show LimitsDTO, LimitDTO, LimitsMapper;

frontend/packages/sxchnge_wallet/.gitignore

@@ -0,0 +1,3 @@
+.dart_tool/
+build/
+pubspec.lock

frontend/packages/sxchnge_wallet/README.md

@@ -0,0 +1,48 @@
+# SXCHNGE wallet
+
+Shared Flutter domain, injectable services and providers for accounts, quotes,
+operations, limits synchronization and account language. Web and mobile clients
+consume the same models; widgets do not call transport APIs.
+
+`WalletService` returns mapped domain models. `DummyWalletService` is an in-memory
+backend stand-in; `WalletProvider` owns snapshots and pending-operation refresh,
+`TransferProvider` owns draft/review/submission/reconciliation, and
+`WorkspaceLimitsProvider` refetches the separate `LimitsService` projection when
+wallet state changes. The adapter reuses the KYC package's limit DTO and mapper.
+
+## Demo behavior
+
+- Opening balances: EUR 75, USD 0, GBP 0. No invented historical transactions.
+- Fixed demo ratios: EUR/USD 1.1; GBP uses weight 1300 vs EUR 1100 and USD 1000.
+- Top-up fee zero; exchange fee 0.5% rounded down, minimum one minor unit;
+  payout fee 100 minor units. Quote expiry is 60 seconds.
+- Top-ups credit only after settlement. Outgoing total debit includes the fee;
+  it leaves available balance on acceptance. Failed outgoing operations restore
+  that exact total. Exchange destination credits only on completion.
+- Outgoing usage, including fees, is converted upward to EUR minor units.
+  Basic caps: EUR 100/day and 500/month; verified: 2500/day and 10000/month.
+  Top-ups do not consume outgoing capacity. Windows follow the stub's local clock.
+  Policy, usage and remaining are returned by the service, not set in widgets.
+- Submission rechecks balance, limits and expiry, is idempotent by request key,
+  and permits a quote to execute only once. Unknown outcomes reconcile before
+  any resubmission. `nextError`, `loseNextResponse`, `failNextOperation`, injectable
+  clock/delays support deterministic failure testing.
+- Everything resets on application reload. Recipient values are demo text only;
+  no bank details, payment provider, storage or real money movement is connected.
+
+## Integration boundary
+
+Replace `WalletService` and `LimitsService` together with authenticated backend
+adapters. The backend must provide authorization, authoritative quotes/balances,
+atomic limits enforcement, durable idempotency and operation reconciliation.
+Add supported payment methods and validated recipients from that contract, rather
+than interpreting the demo input as production bank validation. Replace profile
+storage with the signed-in account endpoint. No authorization is supplied by
+public demo routes or an available balance.
+
+Analytics use the shared typed recorder: draft, quote, submission and authoritative
+settlement. Retried submissions keep a journey; each accepted operation closes
+once on success/failure. Closing the app while pending does not count as draft
+abandonment. No amounts, account IDs or recipient data enter events. All demo
+signals are simulated. Cross-session outcomes require backend event delivery;
+client-only analytics are not production accounting or conversion evidence.

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

@@ -0,0 +1,113 @@
+enum TransferKind { topUp, exchange, payout }
+
+enum OperationStatus { pending, completed, failed }
+
+enum WalletError {
+  unavailable,
+  invalidAmount,
+  insufficientFunds,
+  limitExceeded,
+  expiredQuote,
+  invalidRecipient,
+  unsupported,
+  notFound,
+  uncertain,
+}
+
+class WalletException implements Exception {
+  const WalletException(this.code);
+  final WalletError code;
+}
+
+class CurrencyAccount {
+  const CurrencyAccount({
+    required this.id,
+    required this.currency,
+    required this.precision,
+    required this.available,
+  });
+  final String id, currency;
+  final int precision, available;
+
+  /// Locale-aware decimal input, integer money. Grouping/exponents are rejected.
+  int? parse(String input) {
+    final value = input.trim().replaceAll(',', '.');
+    if (!RegExp(r'^\d+(\.\d+)?$').hasMatch(value)) return null;
+    final parts = value.split('.');
+    if (parts.length > 1 && parts[1].length > precision) return null;
+    final major = int.tryParse(parts[0]);
+    if (major == null || major > 100000000) return null;
+    final fraction = parts.length > 1
+        ? int.parse(parts[1].padRight(precision, '0'))
+        : 0;
+    return major * scale + fraction;
+  }
+
+  int get scale {
+    var v = 1;
+    for (var i = 0; i < precision; i++) {
+      v *= 10;
+    }
+    return v;
+  }
+}
+
+class TransferRequest {
+  const TransferRequest({
+    required this.kind,
+    required this.source,
+    required this.amount,
+    this.destination,
+    this.recipient = '',
+  });
+  final TransferKind kind;
+  final String source;
+  final int amount;
+  final String? destination;
+  final String recipient;
+}
+
+class Quote {
+  const Quote({
+    required this.id,
+    required this.request,
+    required this.fee,
+    required this.debit,
+    required this.credit,
+    required this.expiresAt,
+    required this.rateNumerator,
+    required this.rateDenominator,
+  });
+  final String id;
+  final TransferRequest request;
+  final int fee, debit, credit, rateNumerator, rateDenominator;
+  final DateTime expiresAt;
+}
+
+class WalletOperation {
+  const WalletOperation({
+    required this.id,
+    required this.quote,
+    required this.status,
+    required this.createdAt,
+  });
+  final String id;
+  final Quote quote;
+  final OperationStatus status;
+  final DateTime createdAt;
+}
+
+class WalletSnapshot {
+  WalletSnapshot({
+    required List<CurrencyAccount> accounts,
+    required List<WalletOperation> operations,
+  }) : accounts = List.unmodifiable(accounts),
+       operations = List.unmodifiable(operations);
+  final List<CurrencyAccount> accounts;
+  final List<WalletOperation> operations;
+}
+
+class AccountProfile {
+  const AccountProfile(this.locale);
+  final String locale;
+}

frontend/packages/sxchnge_wallet/lib/src/providers/limits.dart

@@ -0,0 +1,25 @@
+import 'package:sxchnge_kyc/sxchnge_kyc.dart';
+
+import '../models/wallet.dart';
+import 'wallet.dart';
+
+/// Refetch the backend projection when an operation changes the wallet.
+class WorkspaceLimitsProvider extends LimitsProvider {
+  WorkspaceLimitsProvider(super.service, this.wallet) {
+    _snapshot = wallet.data;
+    wallet.addListener(_changed);
+  }
+  final WalletProvider wallet;
+  WalletSnapshot? _snapshot;
+  void _changed() {
+    if (identical(_snapshot, wallet.data)) return;
+    _snapshot = wallet.data;
+    refresh();
+  }
+
+  @override
+  void dispose() {
+    wallet.removeListener(_changed);
+    super.dispose();
+  }
+}

frontend/packages/sxchnge_wallet/lib/src/providers/transfer.dart

@@ -0,0 +1,213 @@
+import 'dart:math';
+
+import 'package:flutter/foundation.dart';
+
+import 'package:sxchnge_analytics/sxchnge_analytics.dart';
+
+import '../models/wallet.dart';
+import 'wallet.dart';
+
+class TransferProvider extends ChangeNotifier {
+  TransferProvider(this.wallet, this.kind, {String? source})
+    : source = source ?? wallet.data?.accounts.firstOrNull?.id ?? 'eur',
+      recorder = JourneyRecorder(wallet.analytics) {
+    destination =
+        wallet.data?.accounts
+            .where((a) => a.id != this.source)
+            .firstOrNull
+            ?.id ??
+        'usd';
+    final op = recorder.begin(
+      journey,
+      JourneyStep.transferDraft,
+      simulated: wallet.service.isSimulated,
+    );
+    recorder.finish(op, simulated: wallet.service.isSimulated);
+  }
+  final WalletProvider wallet;
+  final TransferKind kind;
+  final JourneyRecorder recorder;
+  String source;
+  String? destination;
+  String amount = '', recipient = '';
+  Quote? quote;
+  WalletOperation? result;
+  WalletError? error;
+  bool noSubmission = false;
+  bool busy = false, uncertain = false, _disposed = false, _handedOff = false;
+  int _revision = 0;
+  String? _key;
+  JourneyKind get journey => switch (kind) {
+    TransferKind.topUp => JourneyKind.topUp,
+    TransferKind.exchange => JourneyKind.exchange,
+    TransferKind.payout => JourneyKind.payout,
+  };
+  bool get hasDraft => amount.isNotEmpty || recipient.isNotEmpty;
+  bool get expired =>
+      quote != null && !DateTime.now().isBefore(quote!.expiresAt);
+  void change({
+    String? source,
+    String? destination,
+    String? amount,
+    String? recipient,
+  }) {
+    if (busy || uncertain) return;
+    this.source = source ?? this.source;
+    this.destination = destination ?? this.destination;
+    this.amount = amount ?? this.amount;
+    this.recipient = recipient ?? this.recipient;
+    quote = null;
+    noSubmission = false;
+    error = null;
+    _key = null;
+    _revision++;
+    notifyListeners();
+  }
+
+  void edit() {
+    if (!busy && !uncertain) {
+      quote = null;
+      error = null;
+      _key = null;
+      notifyListeners();
+    }
+  }
+
+  Future<void> review() async {
+    if (busy || uncertain) return;
+    final money = wallet.account(source)?.parse(amount);
+    if (money == null || money <= 0) {
+      error = WalletError.invalidAmount;
+      notifyListeners();
+      return;
+    }
+    busy = true;
+    noSubmission = false;
+    error = null;
+    notifyListeners();
+    final revision = ++_revision;
+    final op = recorder.begin(
+      journey,
+      JourneyStep.transferQuote,
+      simulated: wallet.service.isSimulated,
+    );
+    try {
+      final q = await wallet.service.quote(
+        TransferRequest(
+          kind: kind,
+          source: source,
+          amount: money,
+          destination: kind == TransferKind.exchange ? destination : null,
+          recipient: recipient.trim(),
+        ),
+      );
+      if (_disposed || revision != _revision) return;
+      quote = q;
+      _key = null;
+      recorder.finish(op, simulated: wallet.service.isSimulated);
+    } catch (e) {
+      if (_disposed) return;
+      error = _code(e);
+      recorder.finish(op, failure: _failure(error!));
+    }
+    if (_disposed) return;
+    busy = false;
+    notifyListeners();
+  }
+
+  Future<void> submit() async {
+    if (busy || quote == null || uncertain) return;
+    if (expired) {
+      error = WalletError.expiredQuote;
+      notifyListeners();
+      return;
+    }
+    busy = true;
+    noSubmission = false;
+    error = null;
+    notifyListeners();
+    _key ??= List.generate(
+      16,
+      (_) => Random.secure().nextInt(256).toRadixString(16).padLeft(2, '0'),
+    ).join();
+    final op = recorder.begin(
+      journey,
+      JourneyStep.transferSubmission,
+      simulated: wallet.service.isSimulated,
+    );
+    try {
+      final r = await wallet.service.submit(quote!.id, _key!);
+      if (_disposed) return;
+      _accepted(r, op);
+    } catch (e) {
+      if (_disposed) return;
+      error = _code(e);
+      // All transport/unexpected failures are ambiguous after execution started.
+      uncertain = [
+        WalletError.unavailable,
+        WalletError.uncertain,
+      ].contains(error);
+      recorder.finish(op, failure: _failure(error!));
+    }
+    if (_disposed) return;
+    busy = false;
+    notifyListeners();
+  }
+
+  void _accepted(WalletOperation value, JourneyOperation op) {
+    result = value;
+    uncertain = false;
+    error = null;
+    recipient = '';
+    recorder.finish(op, simulated: wallet.service.isSimulated);
+    wallet.track(value, recorder, journey);
+    _handedOff = true;
+  }
+
+  Future<void> reconcile() async {
+    if (busy || !uncertain || _key == null) return;
+    busy = true;
+    noSubmission = false;
+    error = null;
+    notifyListeners();
+    final op = recorder.begin(
+      journey,
+      JourneyStep.transferSubmission,
+      simulated: wallet.service.isSimulated,
+    );
+    try {
+      final r = await wallet.service.findSubmission(_key!);
+      if (_disposed) return;
+      if (r != null) {
+        _accepted(r, op);
+      } else {
+        uncertain = false;
+        noSubmission = true;
+        recorder.finish(op, simulated: wallet.service.isSimulated);
+      }
+    } catch (e) {
+      if (_disposed) return;
+      error = _code(e);
+      recorder.finish(op, failure: JourneyFailure.unavailable);
+    }
+    if (_disposed) return;
+    busy = false;
+    notifyListeners();
+  }
+
+  WalletError _code(Object e) =>
+      e is WalletException ? e.code : WalletError.unavailable;
+  JourneyFailure _failure(WalletError e) => switch (e) {
+    WalletError.insufficientFunds => JourneyFailure.insufficientFunds,
+    WalletError.limitExceeded => JourneyFailure.limitExceeded,
+    WalletError.expiredQuote => JourneyFailure.expired,
+    _ => JourneyFailure.unavailable,
+  };
+  @override
+  void dispose() {
+    _disposed = true;
+    recipient = '';
+    if (!_handedOff) recorder.dispose();
+    super.dispose();
+  }
+}

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

@@ -0,0 +1,150 @@
+import 'dart:async';
+
+import 'package:flutter/foundation.dart';
+
+import 'package:sxchnge_analytics/sxchnge_analytics.dart';
+
+import '../models/wallet.dart';
+import '../services/contracts.dart';
+
+class WalletProvider extends ChangeNotifier {
+  WalletProvider(this.service, this.analytics);
+  final WalletService service;
+  final AnalyticsService analytics;
+  WalletSnapshot? data;
+  bool loading = false,
+      failed = false,
+      profileLoading = false,
+      profileFailed = false,
+      saving = false,
+      saveFailed = false;
+  String? preferredLocale;
+  bool _disposed = false;
+  int _revision = 0;
+  Timer? _poll;
+  final _settlements = <String, (JourneyRecorder, JourneyOperation)>{};
+  CurrencyAccount? account(String? id) {
+    for (final a in data?.accounts ?? <CurrencyAccount>[]) {
+      if (a.id == id) return a;
+    }
+    return null;
+  }
+
+  WalletOperation? operation(String id) {
+    for (final o in data?.operations ?? <WalletOperation>[]) {
+      if (o.id == id) return o;
+    }
+    return null;
+  }
+
+  bool get hasPending =>
+      data?.operations.any((o) => o.status == OperationStatus.pending) ?? false;
+  Future<void> refresh() async {
+    final rev = ++_revision;
+    loading = true;
+    failed = false;
+    notifyListeners();
+    try {
+      final result = await service.fetch();
+      if (_disposed || rev != _revision) return;
+      data = result;
+      for (final o in result.operations) {
+        if (o.status == OperationStatus.pending) continue;
+        final pair = _settlements.remove(o.id);
+        if (pair != null) {
+          pair.$1.finish(
+            pair.$2,
+            simulated: service.isSimulated,
+            failure: o.status == OperationStatus.failed
+                ? JourneyFailure.declined
+                : null,
+            terminal: true,
+          );
+          pair.$1.dispose();
+        }
+      }
+    } catch (_) {
+      if (_disposed || rev != _revision) return;
+      failed = true;
+    }
+    if (_disposed || rev != _revision) return;
+    loading = false;
+    _poll?.cancel();
+    if (hasPending) {
+      _poll = Timer(const Duration(seconds: 3), () {
+        if (!_disposed) refresh();
+      });
+    }
+    notifyListeners();
+  }
+
+  void track(
+    WalletOperation operation,
+    JourneyRecorder recorder,
+    JourneyKind kind,
+  ) {
+    final step = recorder.begin(
+      kind,
+      JourneyStep.settlement,
+      simulated: service.isSimulated,
+    );
+    _settlements[operation.id] = (recorder, step);
+    final snapshot = data;
+    if (snapshot != null) {
+      data = WalletSnapshot(
+        accounts: snapshot.accounts,
+        operations: [
+          operation,
+          ...snapshot.operations.where((o) => o.id != operation.id),
+        ],
+      );
+    }
+    unawaited(refresh());
+  }
+
+  Future<void> loadProfile() async {
+    if (profileLoading) return;
+    profileLoading = true;
+    profileFailed = false;
+    notifyListeners();
+    try {
+      final result = await service.profile();
+      if (_disposed) return;
+      preferredLocale = result.locale;
+    } catch (_) {
+      if (_disposed) return;
+      profileFailed = true;
+    }
+    profileLoading = false;
+    notifyListeners();
+  }
+
+  Future<bool> saveLocale(String locale) async {
+    if (saving) return false;
+    saving = true;
+    saveFailed = false;
+    notifyListeners();
+    try {
+      final result = await service.saveLocale(locale);
+      if (_disposed) return false;
+      preferredLocale = result.locale;
+    } catch (_) {
+      if (_disposed) return false;
+      saveFailed = true;
+    }
+    saving = false;
+    notifyListeners();
+    return !saveFailed;
+  }
+
+  @override
+  void dispose() {
+    _disposed = true;
+    _poll?.cancel();
+    for (final p in _settlements.values) {
+      p.$1.dispose(abandonActive: false);
+    }
+    _settlements.clear();
+    super.dispose();
+  }
+}

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

@@ -0,0 +1,13 @@
+import '../models/wallet.dart';
+
+abstract interface class WalletService {
+  bool get isSimulated;
+  Future<WalletSnapshot> fetch();
+  Future<Quote> quote(TransferRequest request);
+
+  /// Same key must reconcile uncertain submissions without duplicate execution.
+  Future<WalletOperation> submit(String quoteId, String idempotencyKey);
+  Future<WalletOperation?> findSubmission(String idempotencyKey);
+  Future<AccountProfile> profile();
+  Future<AccountProfile> saveLocale(String locale);
+}

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

@@ -0,0 +1,259 @@
+import 'dart:math';
+
+import 'package:sxchnge_kyc/limits_transport.dart';
+import 'package:sxchnge_kyc/sxchnge_kyc.dart';
+
+import '../models/wallet.dart';
+import '../transport/wallet.dart';
+import 'contracts.dart';
+
+/// Coherent, account-scoped backend stand-in. No network or persistence.
+class DummyWalletService implements WalletService {
+  DummyWalletService(
+    this.identity, {
+    this.delay = const Duration(milliseconds: 350),
+    this.settlement = const Duration(seconds: 2),
+    DateTime Function()? now,
+    String initialLocale = 'en',
+  }) : now = now ?? DateTime.now,
+       _locale = initialLocale;
+  final IdentityService identity;
+  final Duration delay, settlement;
+  final DateTime Function() now;
+  final _accounts = [
+    AccountDTO('eur', 'EUR', 2, 7500),
+    AccountDTO('usd', 'USD', 2, 0),
+    AccountDTO('gbp', 'GBP', 2, 0),
+  ];
+  final Map<String, QuoteDTO> _quotes = {};
+  final _usedQuotes = <String>{};
+  final Map<String, OperationDTO> _submissions = {};
+  String _locale;
+  int _serial = 0;
+  WalletError? nextError;
+  bool failNextOperation = false;
+  bool loseNextResponse = false;
+  @override
+  bool get isSimulated => true;
+  Future<void> _wait() async {
+    await Future<void>.delayed(delay);
+    final error = nextError;
+    nextError = null;
+    if (error != null) throw WalletException(error);
+  }
+
+  AccountDTO _account(String id) => _accounts.firstWhere(
+    (a) => a.id == id,
+    orElse: () => throw const WalletException(WalletError.notFound),
+  );
+  // Fixed demo ratios to EUR; never marketed as live rates.
+  int _weight(String id) => switch (id) {
+    'eur' => 1100,
+    'usd' => 1000,
+    'gbp' => 1300,
+    _ => throw const WalletException(WalletError.unsupported),
+  };
+  int _eur(int minor, String id) => (minor * _weight(id) + 1099) ~/ 1100;
+  void _settle() {
+    for (final o in _submissions.values) {
+      if (o.status != 'pending' || now().isBefore(o.ready)) continue;
+      o.status = o.fail ? 'failed' : 'completed';
+      final q = o.quote;
+      if (o.fail) {
+        if (q.request.kind != 'topUp')
+          _account(q.request.source).available += q.debit;
+      } else if (q.request.kind == 'topUp') {
+        _account(q.request.source).available += q.credit;
+      } else if (q.request.kind == 'exchange') {
+        _account(q.request.destination!).available += q.credit;
+      }
+    }
+  }
+
+  int _usage({required bool monthly, required bool pending}) {
+    final current = now();
+    return _submissions.values
+        .where(
+          (o) =>
+              o.quote.request.kind != 'topUp' &&
+              o.status == (pending ? 'pending' : 'completed') &&
+              o.created.year == current.year &&
+              o.created.month == current.month &&
+              (monthly || o.created.day == current.day),
+        )
+        .fold(
+          0,
+          (total, o) => total + _eur(o.quote.debit, o.quote.request.source),
+        );
+  }
+
+  Future<bool> _verified() async =>
+      (await identity.fetch()).status == IdentityStatus.approved;
+  void _check(QuoteDTO q, bool verified) {
+    if (q.request.kind == 'topUp') return;
+    if (_account(q.request.source).available < q.debit)
+      throw const WalletException(WalletError.insufficientFunds);
+    final charge = _eur(q.debit, q.request.source);
+    if (charge +
+                _usage(monthly: false, pending: false) +
+                _usage(monthly: false, pending: true) >
+            (verified ? 250000 : 10000) ||
+        charge +
+                _usage(monthly: true, pending: false) +
+                _usage(monthly: true, pending: true) >
+            (verified ? 1000000 : 50000))
+      throw const WalletException(WalletError.limitExceeded);
+  }
+
+  @override
+  Future<WalletSnapshot> fetch() async {
+    await _wait();
+    _settle();
+    return WalletSnapshot(
+      accounts: _accounts.map(WalletMapper.account).toList(),
+      operations: _submissions.values
+          .toList()
+          .reversed
+          .map(WalletMapper.operation)
+          .toList(),
+    );
+  }
+
+  @override
+  Future<Quote> quote(TransferRequest r) async {
+    await _wait();
+    _settle();
+    _account(r.source);
+    if (r.amount <= 0 || r.amount > 100000000)
+      throw const WalletException(WalletError.invalidAmount);
+    if (r.kind == TransferKind.exchange &&
+        (r.source == r.destination || r.destination == null))
+      throw const WalletException(WalletError.unsupported);
+    if (r.kind == TransferKind.payout &&
+        (r.recipient.trim().length < 6 || r.recipient.length > 140))
+      throw const WalletException(WalletError.invalidRecipient);
+    if (r.kind == TransferKind.exchange) _account(r.destination!);
+    final fee = switch (r.kind) {
+      TransferKind.topUp => 0,
+      TransferKind.exchange => max(1, r.amount ~/ 200),
+      TransferKind.payout => 100,
+    };
+    final n = r.kind == TransferKind.exchange ? _weight(r.source) : 1;
+    final d = r.kind == TransferKind.exchange ? _weight(r.destination!) : 1;
+    final q = QuoteDTO(
+      'quote-${++_serial}',
+      WalletMapper.request(r),
+      fee,
+      r.kind == TransferKind.topUp ? r.amount : r.amount + fee,
+      r.amount * n ~/ d,
+      now().add(const Duration(seconds: 60)),
+      n,
+      d,
+    );
+    if (q.credit <= 0) throw const WalletException(WalletError.invalidAmount);
+    final verified = await _verified();
+    _settle();
+    _check(q, verified);
+    _quotes[q.id] = q;
+    return WalletMapper.quote(q);
+  }
+
+  @override
+  Future<WalletOperation> submit(String quoteId, String idempotencyKey) async {
+    await _wait();
+    if (_submissions.containsKey(idempotencyKey))
+      return WalletMapper.operation(_submissions[idempotencyKey]!);
+    final q = _quotes[quoteId];
+    if (q == null) throw const WalletException(WalletError.expiredQuote);
+    final verified = await _verified();
+    _settle();
+    if (_submissions.containsKey(idempotencyKey))
+      return WalletMapper.operation(_submissions[idempotencyKey]!);
+    if (!now().isBefore(q.expires))
+      throw const WalletException(WalletError.expiredQuote);
+    if (_usedQuotes.contains(q.id))
+      throw const WalletException(WalletError.expiredQuote);
+    _check(q, verified);
+    _usedQuotes.add(q.id);
+    if (q.request.kind != 'topUp')
+      _account(q.request.source).available -= q.debit;
+    final o = OperationDTO(
+      'op-${++_serial}',
+      q,
+      now(),
+      now().add(settlement),
+      fail: failNextOperation,
+    );
+    failNextOperation = false;
+    _submissions[idempotencyKey] = o;
+    if (loseNextResponse) {
+      loseNextResponse = false;
+      throw const WalletException(WalletError.uncertain);
+    }
+    return WalletMapper.operation(o);
+  }
+
+  @override
+  Future<WalletOperation?> findSubmission(String key) async {
+    await _wait();
+    _settle();
+    final o = _submissions[key];
+    return o == null ? null : WalletMapper.operation(o);
+  }
+
+  @override
+  Future<AccountProfile> profile() async {
+    await _wait();
+    return WalletMapper.profile(_locale);
+  }
+
+  @override
+  Future<AccountProfile> saveLocale(String locale) async {
+    await _wait();
+    if (!['en', 'ru'].contains(locale))
+      throw const WalletException(WalletError.unsupported);
+    _locale = locale;
+    return WalletMapper.profile(_locale);
+  }
+
+  // Kept separate from wallet fetch because LimitsService has a different result.
+  Future<Limits> fetchLimits() async {
+    await _wait();
+    final verified = await _verified();
+    _settle();
+    final rows = <LimitDTO>[];
+    for (final monthly in [false, true]) {
+      final basic = monthly ? 50000 : 10000;
+      final upgraded = monthly ? 1000000 : 250000;
+      final current = verified ? upgraded : basic;
+      final used = _usage(monthly: monthly, pending: false);
+      final pending = _usage(monthly: monthly, pending: true);
+      rows.add(
+        LimitDTO(
+          monthly ? 'month' : 'day',
+          'EUR',
+          basic,
+          upgraded,
+          current,
+          max(0, current - used - pending),
+          used,
+          pending,
+        ),
+      );
+    }
+    return LimitsMapper.fromDTO(
+      LimitsDTO(
+        tier: verified ? 'verified' : 'basic',
+        rows: rows,
+        simulated: true,
+      ),
+    );
+  }
+}
+
+class WalletLimitsService implements LimitsService {
+  const WalletLimitsService(this.wallet);
+  final DummyWalletService wallet;
+  @override
+  Future<Limits> fetch() => wallet.fetchLimits();
+}

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

@@ -0,0 +1,89 @@
+import '../models/wallet.dart';
+
+class AccountDTO {
+  AccountDTO(this.id, this.currency, this.precision, this.available);
+  final String id, currency;
+  final int precision;
+  int available;
+}
+
+class RequestDTO {
+  const RequestDTO(
+    this.kind,
+    this.source,
+    this.destination,
+    this.amount,
+    this.recipient,
+  );
+  final String kind, source, recipient;
+  final String? destination;
+  final int amount;
+}
+
+class QuoteDTO {
+  const QuoteDTO(
+    this.id,
+    this.request,
+    this.fee,
+    this.debit,
+    this.credit,
+    this.expires,
+    this.numerator,
+    this.denominator,
+  );
+  final String id;
+  final RequestDTO request;
+  final int fee, debit, credit, numerator, denominator;
+  final DateTime expires;
+}
+
+class OperationDTO {
+  OperationDTO(
+    this.id,
+    this.quote,
+    this.created,
+    this.ready, {
+    this.status = 'pending',
+    this.fail = false,
+  });
+  final String id;
+  final QuoteDTO quote;
+  final DateTime created, ready;
+  String status;
+  final bool fail;
+}
+
+abstract final class WalletMapper {
+  static CurrencyAccount account(AccountDTO d) => CurrencyAccount(
+    id: d.id,
+    currency: d.currency,
+    precision: d.precision,
+    available: d.available,
+  );
+  static RequestDTO request(TransferRequest r) =>
+      RequestDTO(r.kind.name, r.source, r.destination, r.amount, r.recipient);
+  static TransferRequest fromRequest(RequestDTO d) => TransferRequest(
+    kind: TransferKind.values.byName(d.kind),
+    source: d.source,
+    destination: d.destination,
+    amount: d.amount,
+    recipient: d.recipient,
+  );
+  static Quote quote(QuoteDTO d) => Quote(
+    id: d.id,
+    request: fromRequest(d.request),
+    fee: d.fee,
+    debit: d.debit,
+    credit: d.credit,
+    expiresAt: d.expires,
+    rateNumerator: d.numerator,
+    rateDenominator: d.denominator,
+  );
+  static WalletOperation operation(OperationDTO d) => WalletOperation(
+    id: d.id,
+    quote: quote(d.quote),
+    status: OperationStatus.values.byName(d.status),
+    createdAt: d.created,
+  );
+  static AccountProfile profile(String locale) => AccountProfile(locale);
+}

frontend/packages/sxchnge_wallet/lib/sxchnge_wallet.dart

@@ -0,0 +1,6 @@
+export 'src/models/wallet.dart';
+export 'src/providers/wallet.dart';
+export 'src/providers/transfer.dart';
+export 'src/services/contracts.dart';
+export 'src/services/dummy.dart';
+export 'src/providers/limits.dart';

frontend/packages/sxchnge_wallet/pubspec.yaml

@@ -0,0 +1,17 @@
+name: sxchnge_wallet
+description: Shared currency accounts, transaction flows and account preferences.
+version: 0.1.0
+publish_to: none
+environment:
+  sdk: '>=3.13.0 <4.0.0'
+  flutter: '>=3.47.0'
+dependencies:
+  flutter:
+    sdk: flutter
+  sxchnge_analytics:
+    path: ../sxchnge_analytics
+  sxchnge_kyc:
+    path: ../sxchnge_kyc
+dev_dependencies:
+  flutter_test:
+    sdk: flutter

frontend/packages/sxchnge_wallet/test/wallet_test.dart

@@ -0,0 +1,289 @@
+import 'dart:async';
+
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:sxchnge_analytics/sxchnge_analytics.dart';
+
+import 'package:sxchnge_kyc/sxchnge_kyc.dart';
+
+import 'package:sxchnge_wallet/sxchnge_wallet.dart';
+
+void main() {
+  late DateTime now;
+  late DummyWalletService s;
+  late WalletProvider wallet;
+  late DummyAnalyticsService analytics;
+  setUp(() {
+    now = DateTime(2026, 9, 12, 10);
+    s = DummyWalletService(
+      DummyIdentityService(delay: Duration.zero),
+      delay: Duration.zero,
+      now: () => now,
+    );
+    analytics = DummyAnalyticsService();
+    wallet = WalletProvider(s, analytics);
+  });
+  tearDown(() => wallet.dispose());
+  Future<WalletOperation> transfer(
+    TransferKind kind,
+    int amount, {
+    String source = 'eur',
+    String? to,
+    String recipient = 'Sample recipient',
+    String key = 'one',
+  }) async {
+    final q = await s.quote(
+      TransferRequest(
+        kind: kind,
+        source: source,
+        destination: to,
+        amount: amount,
+        recipient: recipient,
+      ),
+    );
+    return s.submit(q.id, key);
+  }
+
+  test(
+    'funding credits only on completion; history and available balance agree',
+    () async {
+      final o = await transfer(TransferKind.topUp, 2500);
+      expect(o.status, OperationStatus.pending);
+      expect((await s.fetch()).accounts.first.available, 7500);
+      now = now.add(const Duration(seconds: 3));
+      final state = await s.fetch();
+      expect(state.accounts.first.available, 10000);
+      expect(state.operations.single.status, OperationStatus.completed);
+    },
+  );
+  test(
+    'exchange debits total once, then credits target and updates usage',
+    () async {
+      final q = await s.quote(
+        const TransferRequest(
+          kind: TransferKind.exchange,
+          source: 'eur',
+          destination: 'usd',
+          amount: 2000,
+        ),
+      );
+      expect(q.debit, 2010);
+      expect(q.credit, 2200);
+      await Future.wait([s.submit(q.id, 'same'), s.submit(q.id, 'same')]);
+      var data = await s.fetch();
+      expect(data.accounts.first.available, 5490);
+      expect(data.accounts[1].available, 0);
+      expect(data.operations.length, 1);
+      var limits = await s.fetchLimits();
+      expect(limits.rows.first.reservedMinor, 2010);
+      expect(limits.rows.first.usedMinor, 0);
+      now = now.add(const Duration(seconds: 3));
+      data = await s.fetch();
+      expect(data.accounts[1].available, 2200);
+      limits = await s.fetchLimits();
+      expect(limits.rows.first.usedMinor, 2010);
+      expect(limits.rows.first.reservedMinor, 0);
+      expect(limits.rows.first.remainingMinor, 7990);
+      await expectLater(
+        s.submit(q.id, 'different'),
+        throwsA(isA<WalletException>()),
+      );
+    },
+  );
+  test('failed payout restores amount and fee, releases limit usage', () async {
+    s.failNextOperation = true;
+    await transfer(TransferKind.payout, 2000);
+    expect((await s.fetch()).accounts.first.available, 5400);
+    now = now.add(const Duration(seconds: 3));
+    final data = await s.fetch();
+    expect(data.accounts.first.available, 7500);
+    expect(data.operations.single.status, OperationStatus.failed);
+    expect((await s.fetchLimits()).rows.first.remainingMinor, 10000);
+  });
+  test('expired quotes and stale balance cannot execute', () async {
+    final q = await s.quote(
+      const TransferRequest(
+        kind: TransferKind.payout,
+        source: 'eur',
+        amount: 7000,
+        recipient: 'Sample recipient',
+      ),
+    );
+    now = now.add(const Duration(seconds: 61));
+    await expectLater(
+      s.submit(q.id, 'expired'),
+      throwsA(
+        isA<WalletException>().having(
+          (e) => e.code,
+          'code',
+          WalletError.expiredQuote,
+        ),
+      ),
+    );
+    expect((await s.fetch()).accounts.first.available, 7500);
+    final a = await s.quote(
+      const TransferRequest(
+        kind: TransferKind.payout,
+        source: 'eur',
+        amount: 6000,
+        recipient: 'Sample recipient',
+      ),
+    );
+    final b = await s.quote(
+      const TransferRequest(
+        kind: TransferKind.payout,
+        source: 'eur',
+        amount: 6000,
+        recipient: 'Sample recipient',
+      ),
+    );
+    await s.submit(a.id, 'first');
+    await expectLater(
+      s.submit(b.id, 'second'),
+      throwsA(
+        isA<WalletException>().having(
+          (e) => e.code,
+          'code',
+          WalletError.insufficientFunds,
+        ),
+      ),
+    );
+  });
+  test('limits block a funded account independently of balance', () async {
+    await transfer(TransferKind.topUp, 20000);
+    now = now.add(const Duration(seconds: 3));
+    await s.fetch();
+    await expectLater(
+      s.quote(
+        const TransferRequest(
+          kind: TransferKind.payout,
+          source: 'eur',
+          amount: 11000,
+          recipient: 'Sample recipient',
+        ),
+      ),
+      throwsA(
+        isA<WalletException>().having(
+          (e) => e.code,
+          'code',
+          WalletError.limitExceeded,
+        ),
+      ),
+    );
+  });
+  test('decimal parser accepts locale decimal, rejects grouping and excess precision', () {
+    const a = CurrencyAccount(
+      id: 'eur',
+      currency: 'EUR',
+      precision: 2,
+      available: 0,
+    );
+    expect(a.parse('12,34'), 1234);
+    expect(a.parse('12.3'), 1230);
+    expect(a.parse('1,000.00'), null);
+    expect(a.parse('1.234'), null);
+    expect(a.parse('-2'), null);
+    expect(a.parse('1e5'), null);
+  });
+  test(
+    'preferences are service-owned; failed save preserves stored locale',
+    () async {
+      expect((await s.profile()).locale, 'en');
+      await wallet.saveLocale('ru');
+      expect((await s.profile()).locale, 'ru');
+      s.nextError = WalletError.unavailable;
+      expect(await wallet.saveLocale('en'), false);
+      expect((await s.profile()).locale, 'ru');
+      expect(wallet.saveFailed, true);
+    },
+  );
+  test(
+    'provider reconciles lost response and records settlement once',
+    () async {
+      // Use real-clock quote lifetime for the provider UI expiry check.
+      final service = DummyWalletService(
+        DummyIdentityService(delay: Duration.zero),
+        delay: Duration.zero,
+        settlement: Duration.zero,
+      );
+      final p = WalletProvider(service, analytics);
+      addTearDown(p.dispose);
+      await p.refresh();
+      final draft = TransferProvider(p, TransferKind.exchange);
+      addTearDown(draft.dispose);
+      draft.change(amount: '20');
+      await draft.review();
+      service.loseNextResponse = true;
+      await draft.submit();
+      expect(draft.uncertain, true);
+      expect(draft.result, null);
+      await draft.reconcile();
+      expect(draft.uncertain, false);
+      expect(draft.result, isNotNull);
+      await p.refresh();
+      await p.refresh();
+      await Future<void>.delayed(Duration.zero);
+      expect(p.data!.operations.length, 1);
+      expect(
+        analytics.events
+            .where((e) => e.step == JourneyStep.settlement && e.terminal)
+            .length,
+        1,
+      );
+      expect(
+        analytics.events.every(
+          (e) =>
+              !e.properties.containsKey('amount') &&
+              !e.properties.containsKey('recipient'),
+        ),
+        true,
+      );
+    },
+  );
+  test(
+    'pending operations refresh balances and limits without a detail screen',
+    () async {
+      await wallet.refresh();
+      final limits = WorkspaceLimitsProvider(WalletLimitsService(s), wallet);
+      addTearDown(limits.dispose);
+      await limits.refresh();
+      s.failNextOperation = true;
+      await transfer(TransferKind.payout, 2000);
+      await wallet.refresh();
+      expect(wallet.account('eur')!.available, 5400);
+      now = now.add(const Duration(seconds: 3));
+      final done = Completer<void>();
+      void changed() {
+        if (wallet.operation(wallet.data!.operations.single.id)?.status ==
+                OperationStatus.failed &&
+            !done.isCompleted)
+          done.complete();
+      }
+
+      wallet.addListener(changed);
+      await done.future.timeout(const Duration(seconds: 5));
+      wallet.removeListener(changed);
+      await Future<void>.delayed(const Duration(milliseconds: 20));
+      expect(wallet.account('eur')!.available, 7500);
+      expect(limits.data!.rows.first.remainingMinor, 10000);
+    },
+  );
+  test(
+    'closing a pending operation does not report draft abandonment',
+    () async {
+      final r = JourneyRecorder(analytics);
+      final op = r.begin(
+        JourneyKind.exchange,
+        JourneyStep.settlement,
+        simulated: true,
+      );
+      expect(op, isNotNull);
+      r.dispose(abandonActive: false);
+      await Future<void>.delayed(Duration.zero);
+      expect(
+        analytics.events.any((e) => e.signal == JourneySignal.abandoned),
+        false,
+      );
+    },
+  );
+}