fix(wallet): name wallet records without a seed at the reuse point

lib/core/wallet/domain/inconsistent_wallet_state_exception.dart

@@ -0,0 +1,16 @@
+import 'package:bb_mobile/core/errors/bull_exception.dart';
+
+/// Wallet records exist for [fingerprint] but their seed is no longer in the
+/// seed store (keystore invalidation, interrupted restore), so anything that
+/// derives the xprv is doomed.
+///
+/// Thrown where the records are reused — cold start and default-wallet
+/// creation — so the state is named at detection time instead of surfacing as
+/// a `SeedNotFoundException` inside whichever flow happens to need the xprv
+/// first (#137). The remedy is restoring the wallet from a backup.
+class InconsistentWalletStateException extends BullException {
+  InconsistentWalletStateException({required this.fingerprint})
+    : super('Wallet records without a seed for fingerprint: $fingerprint');
+
+  final String fingerprint;
+}

lib/core/wallet/domain/usecases/create_default_wallets_usecase.dart

@@ -5,6 +5,7 @@ import 'package:bb_mobile/core/settings/data/settings_repository.dart';
 import 'package:bb_mobile/core/utils/logger.dart';
 import 'package:bb_mobile/core/wallet/data/repositories/wallet_repository.dart';
 import 'package:bb_mobile/core/wallet/domain/entities/wallet.dart';
+import 'package:bb_mobile/core/wallet/domain/inconsistent_wallet_state_exception.dart';
 
 class CreateDefaultWalletsUsecase {
   final SeedRepository _seedRepository;
@@ -41,7 +42,14 @@ class CreateDefaultWalletsUsecase {
       );
       final hasBitcoin = existing.any((w) => w.network.isBitcoin);
       final hasLiquid = existing.any((w) => w.network.isLiquid);
-      if (hasBitcoin && hasLiquid) return existing;
+      if (hasBitcoin && hasLiquid) {
+        await _ensureSeedsPresent(
+          existing,
+          mnemonicWords: mnemonicWords,
+          passphrase: passphrase,
+        );
+        return existing;
+      }
 
       final isGenerated = mnemonicWords == null;
       final mnemonic = mnemonicWords ?? _mnemonicGenerator.generate();
@@ -91,10 +99,59 @@ class CreateDefaultWalletsUsecase {
       }
 
       return [...existing, ...created];
+    } on InconsistentWalletStateException {
+      // Its own diagnosis; stringifying it into CreateDefaultWalletsException
+      // would hide the one failure whose remedy is wallet recovery (#137).
+      rethrow;
     } catch (e) {
       throw CreateDefaultWalletsException(e.toString());
     }
   }
+
+  /// Guards the reuse path: records whose seed is gone would otherwise pass as
+  /// "wallets already exist" and blow up later in the first flow that derives
+  /// the xprv. Presence check only — no seed material is read or logged.
+  ///
+  /// When the caller supplied the mnemonic (restore-from-backup) and it is the
+  /// mnemonic these records were built from, the missing seed is simply stored
+  /// back: that is exactly the recovery the exception tells users to perform,
+  /// so it must not itself be rejected as an inconsistent state.
+  Future<void> _ensureSeedsPresent(
+    List<Wallet> wallets, {
+    List<String>? mnemonicWords,
+    String? passphrase,
+  }) async {
+    final fingerprints = wallets.map((w) => w.masterFingerprint).toSet();
+    for (final fingerprint in fingerprints) {
+      if (await _seedRepository.exists(fingerprint)) continue;
+
+      final restorable =
+          mnemonicWords != null &&
+          _seedRepository.fingerprintFor(
+                mnemonicWords: mnemonicWords,
+                passphrase: passphrase,
+              ) ==
+              fingerprint;
+      if (restorable) {
+        await _seedRepository.createFromMnemonic(
+          mnemonicWords: mnemonicWords,
+          passphrase: passphrase,
+        );
+        continue;
+      }
+
+      final inconsistent = InconsistentWalletStateException(
+        fingerprint: fingerprint,
+      );
+      log.severe(
+        message:
+            'CreateDefaultWalletsUsecase: default wallet records without a seed',
+        error: inconsistent,
+        trace: StackTrace.current,
+      );
+      throw inconsistent;
+    }
+  }
 }
 
 class CreateDefaultWalletsException extends BullException {

lib/features/app_startup/domain/usecases/check_for_existing_default_wallets_usecase.dart

@@ -3,6 +3,7 @@ import 'package:bb_mobile/core/settings/data/settings_repository.dart';
 import 'package:bb_mobile/core/utils/logger.dart';
 import 'package:bb_mobile/core/wallet/data/repositories/wallet_repository.dart';
 import 'package:bb_mobile/core/wallet/domain/entities/wallet.dart';
+import 'package:bb_mobile/core/wallet/domain/inconsistent_wallet_state_exception.dart';
 
 class CheckForExistingDefaultWalletsUsecase {
   final SettingsRepository _settingsRepository;
@@ -85,21 +86,26 @@ class CheckForExistingDefaultWalletsUsecase {
     }
 
     log.fine('FINE: found default wallet');
-    await Future.wait(
-      defaultWallets.map((wallet) async {
-        try {
-          await _seedRepository.get(wallet.masterFingerprint);
-          log.fine('FINE: Seed Found');
-        } catch (e) {
-          log.severe(
-            message: 'Seed not found for default wallet ',
-            error: e,
-            trace: StackTrace.current,
-          );
-          rethrow;
-        }
-      }),
-    );
+    // Presence check only — never reads seed material. Records whose seed is
+    // gone are an inconsistent wallet state named here, at the point the
+    // records are reused, instead of a SeedNotFoundException deep inside the
+    // first flow that derives the xprv (#137). `exists` still propagates
+    // KeychainLockedException, which AppStartupBloc treats as transient.
+    final fingerprints = defaultWallets
+        .map((wallet) => wallet.masterFingerprint)
+        .toSet();
+    for (final fingerprint in fingerprints) {
+      if (await _seedRepository.exists(fingerprint)) continue;
+      final inconsistent = InconsistentWalletStateException(
+        fingerprint: fingerprint,
+      );
+      log.severe(
+        message: 'Seed not found for default wallet',
+        error: inconsistent,
+        trace: StackTrace.current,
+      );
+      throw inconsistent;
+    }
     return true;
   }
 }

lib/features/app_startup/ui/app_startup_widget.dart

@@ -3,6 +3,7 @@ import 'package:bb_mobile/core/utils/build_context_x.dart';
 import 'package:bb_mobile/core/utils/constants.dart';
 import 'package:bb_mobile/core/widgets/buttons/button.dart';
 import 'package:bb_mobile/core/widgets/share_logs_widget.dart';
+import 'package:bb_mobile/core/wallet/domain/inconsistent_wallet_state_exception.dart';
 import 'package:bb_mobile/features/app_startup/presentation/bloc/app_startup_bloc.dart';
 import 'package:bb_mobile/features/app_unlock/ui/app_unlock_router.dart';
 import 'package:bb_mobile/features/onboarding/ui/onboarding_router.dart';
@@ -93,6 +94,17 @@ class AppStartupFailureScreen extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    // Wallet records without their seed have one remedy — restore from backup
+    // — so they get their own copy instead of the generic "restart the app"
+    // advice, which can never resolve them (#137).
+    final isInconsistentWalletState = e is InconsistentWalletStateException;
+    final title = isInconsistentWalletState
+        ? context.loc.walletDataIncompleteTitle
+        : context.loc.appStartupErrorTitle;
+    final message = isInconsistentWalletState
+        ? context.loc.walletDataIncompleteRestoreMessage
+        : context.loc.appStartupErrorMessage;
+
     return Scaffold(
       body: Center(
         child: Padding(
@@ -115,7 +127,7 @@ class AppStartupFailureScreen extends StatelessWidget {
                     Icon(Icons.error_outline, color: context.appColors.error),
                     const Gap(8),
                     Text(
-                      context.loc.appStartupErrorTitle,
+                      title,
                       style: context.font.headlineLarge?.copyWith(
                         color: context.appColors.error,
                       ),
@@ -125,7 +137,7 @@ class AppStartupFailureScreen extends StatelessWidget {
                 subtitle: Padding(
                   padding: const EdgeInsets.only(top: 8.0),
                   child: Text(
-                    context.loc.appStartupErrorMessage,
+                    message,
                     style: context.font.bodyMedium?.copyWith(
                       color: context.appColors.secondary.withValues(alpha: 0.7),
                     ),

lib/features/onboarding/domain/onboarding_failure.dart

@@ -8,6 +8,12 @@ final class OnboardingUnexpectedFailure extends OnboardingFailure {
   const OnboardingUnexpectedFailure([super.logMessage]);
 }
 
+/// Default wallet records are on the device without their seed, so onboarding
+/// cannot reuse them; the user has to restore from a backup (#137).
+final class OnboardingInconsistentWalletStateFailure extends OnboardingFailure {
+  const OnboardingInconsistentWalletStateFailure([super.logMessage]);
+}
+
 final class OnboardingBackupVerificationPersistenceFailure
     extends OnboardingFailure {
   const OnboardingBackupVerificationPersistenceFailure([super.logMessage]);

lib/features/onboarding/domain/usecases/create_onboarding_wallets_usecase.dart

@@ -1,6 +1,7 @@
 import 'package:bb_mobile/core/utils/logger.dart';
 import 'package:bb_mobile/core/utils/result.dart';
 import 'package:bb_mobile/core/wallet/domain/entities/wallet.dart';
+import 'package:bb_mobile/core/wallet/domain/inconsistent_wallet_state_exception.dart';
 import 'package:bb_mobile/core/wallet/domain/usecases/create_default_wallets_usecase.dart';
 import 'package:bb_mobile/features/onboarding/domain/onboarding_failure.dart';
 import 'package:meta/meta.dart';
@@ -32,6 +33,17 @@ class CreateOnboardingWalletsUsecase {
         return const Err(failure);
       }
       return Ok(wallets);
+    } on InconsistentWalletStateException catch (error, trace) {
+      log.severe(
+        message: 'createOnboardingWallets found wallet records without a seed',
+        error: error,
+        trace: trace,
+      );
+      return Err(
+        OnboardingInconsistentWalletStateFailure(
+          'wallet records without a seed for ${error.fingerprint}',
+        ),
+      );
     } on CreateDefaultWalletsException catch (error, trace) {
       log.severe(
         message: 'createOnboardingWallets failed',

lib/features/onboarding/presentation/onboarding_failure_l10n.dart

@@ -5,6 +5,8 @@ import 'package:flutter/widgets.dart';
 extension OnboardingFailureL10n on OnboardingFailure {
   String toTranslated(BuildContext context) => switch (this) {
     OnboardingUnexpectedFailure() => context.loc.walletSetupErrorTryAgain,
+    OnboardingInconsistentWalletStateFailure() =>
+      context.loc.walletDataIncompleteRestoreMessage,
     OnboardingBackupVerificationPersistenceFailure() =>
       context.loc.onboardingBackupVerificationSaveFailed,
   };

localization/app_en.arb

@@ -17978,5 +17978,13 @@
   "backupSettingsMetadataAttentionNeeded": "Attention needed",
   "@backupSettingsMetadataAttentionNeeded": {
     "description": "Muted line under the metadata backup status row when a write was rejected or recovery is blocked; never shown for a write that is merely queued"
+  },
+  "walletDataIncompleteTitle": "Wallet data incomplete",
+  "@walletDataIncompleteTitle": {
+    "description": "Title shown when wallet records exist on this device but their seed is missing, so the wallet must be restored from a backup."
+  },
+  "walletDataIncompleteRestoreMessage": "This device still has your wallet records, but the seed that unlocks them is gone. Restore your wallet from your backup on this device to use it again.",
+  "@walletDataIncompleteRestoreMessage": {
+    "description": "Body copy shown when wallet records survive without their seed: the only remedy is restoring the wallet from a backup."
   }
 }