fix: Make transactions atomic / AutoLogout

test/bar_screen_view_model_test.dart

@@ -1,5 +1,4 @@
 import 'package:flutter_test/flutter_test.dart';
-import 'package:kooltab2/models/product.dart';
 import 'package:kooltab2/models/tab_item.dart';
 import 'package:kooltab2/services/bar_tab_service.dart';
 import 'package:kooltab2/services/product_service.dart';
@@ -27,38 +26,28 @@ void main() {
     );
   });
 
-  test(
-    'does not increase a tab item when its product is out of stock',
-    () async {
-      const product = Product(
-        id: 'prod-1',
-        name: 'Chips',
-        category: 'Snacks',
-        stockQuantity: 0,
-        lowStockThreshold: 5,
-        priceInCents: 150,
-      );
-      const item = TabItem(
-        id: 'item-1',
-        tabId: 'tab-1',
-        productId: 'prod-1',
-        productName: 'Chips',
-        quantity: 20,
-        unitPriceInCents: 150,
-      );
+  test('propagates an insufficient-stock error from the transaction', () async {
+    const item = TabItem(
+      id: 'item-1',
+      tabId: 'tab-1',
+      productId: 'prod-1',
+      productName: 'Chips',
+      quantity: 20,
+      unitPriceInCents: 150,
+    );
 
-      when(
-        () => productService.getProducts(),
-      ).thenAnswer((_) async => [product]);
-      await inventory.load();
+    when(
+      () => barTabService.adjustTabItemQuantity(tabItemId: 'item-1', delta: 1),
+    ).thenAnswer((_) async => throw const InsufficientStockException());
 
-      await expectLater(
-        viewModel.changeItemQuantity(item, 21),
-        throwsA(isA<InsufficientStockException>()),
-      );
+    await expectLater(
+      viewModel.changeItemQuantity(item, 1),
+      throwsA(isA<InsufficientStockException>()),
+    );
 
-      expect(viewModel.errorMessage, isNull);
-      verifyNoMoreInteractions(barTabService);
-    },
-  );
+    expect(viewModel.errorMessage, isNull);
+    verify(
+      () => barTabService.adjustTabItemQuantity(tabItemId: 'item-1', delta: 1),
+    ).called(1);
+  });
 }