fix(dashboard): guard pending-transactions emits against post-close StateError

lib/screens/dashboard/bloc/pending_transactions_cubit.dart

@@ -14,9 +14,14 @@ class PendingTransactionsCubit extends Cubit<List<TransactionDto>> {
   Future<void> _loadPendingTransactions() async {
     try {
       final transactions = await _transactionHistoryService.fetchPendingTransactions();
+      // The fetch is started in the constructor and not awaited, so the cubit
+      // can be closed (page popped) before it resolves. Guard the emit to avoid
+      // a StateError after close (issue #657 P3 #16).
+      if (isClosed) return;
       emit(transactions);
     } catch (e) {
       developer.log('Failed to load pending transactions: $e', name: '$PendingTransactionsCubit');
+      if (isClosed) return;
       emit([]);
     }
   }

test/screens/dashboard/pending_transactions_cubit_test.dart

@@ -1,3 +1,5 @@
+import 'dart:async';
+
 import 'package:flutter_test/flutter_test.dart';
 import 'package:mocktail/mocktail.dart';
 import 'package:realunit_wallet/packages/service/dfx/models/transactions/dto/transactions_dto.dart';
@@ -36,6 +38,25 @@ void main() {
       expect(cubit.state, [tx1, tx2]);
     });
 
+    test('does not emit (no StateError) if closed before the fetch resolves '
+        '(issue #657 P3 #16 regression)', () async {
+      final completer = Completer<List<TransactionDto>>();
+      when(() => service.fetchPendingTransactions())
+          .thenAnswer((_) => completer.future);
+
+      final cubit = PendingTransactionsCubit(service);
+      // Close while the constructor-started fetch is still in flight.
+      await cubit.close();
+
+      // Resolving now would, without the isClosed guard, emit after close and
+      // throw 'Cannot emit new states after calling close'.
+      completer.complete([_StubTx()]);
+      await Future<void>.delayed(Duration.zero);
+
+      // No exception escaped; the closed cubit kept its last state.
+      expect(cubit.isClosed, isTrue);
+    });
+
     test('falls back to an empty list when the service throws', () async {
       when(() => service.fetchPendingTransactions())
           .thenAnswer((_) async => throw Exception('network'));