feat: make server owner of tabs

test/product_service_test.dart

@@ -223,7 +223,7 @@ void main() {
         );
       });
 
-      test('throws when not enough stock', () async {
+      test('goes below zero instead of refusing', () async {
         await database
             .into(database.products)
             .insert(
@@ -237,10 +237,10 @@ void main() {
               ),
             );
 
-        expect(
-          () => service.decreaseStock('low-stock', 5),
-          throwsA(isA<InsufficientStockException>()),
-        );
+        await service.decreaseStock('low-stock', 5);
+
+        final product = await service.getProductById('low-stock');
+        expect(product!.stockQuantity, -2);
       });
     });
 
@@ -296,7 +296,7 @@ void main() {
         );
       });
 
-      test('does not allow concurrent decrements below zero', () async {
+      test('counts every concurrent decrement', () async {
         await database
             .into(database.products)
             .insert(
@@ -310,16 +310,13 @@ void main() {
               ),
             );
 
-        await expectLater(
-          Future.wait([
-            service.decreaseStock('concurrent-stock', 1),
-            service.decreaseStock('concurrent-stock', 1),
-          ]),
-          throwsA(isA<InsufficientStockException>()),
-        );
+        await Future.wait([
+          service.decreaseStock('concurrent-stock', 1),
+          service.decreaseStock('concurrent-stock', 1),
+        ]);
 
         final product = await service.getProductById('concurrent-stock');
-        expect(product!.stockQuantity, 0);
+        expect(product!.stockQuantity, -1);
       });
     });