test(shopping): add missing service tests for stale items, dedup, and household isolation

- generateFromPlan removes stale generated items
- sourceRecipes deduplicates when same recipe appears in two slots
- checkItem throws ResourceNotFoundException on household mismatch

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/test/java/com/recipeapp/shopping/ShoppingServiceTest.java

@@ -468,6 +468,97 @@ class ShoppingServiceTest {
                 .isInstanceOf(ResourceNotFoundException.class);
     }
 
+    // ── Generate removes stale items ──
+
+    @Test
+    void generateFromPlanShouldRemoveStaleGeneratedItems() {
+        var household = testHousehold();
+        var plan = testWeekPlan(household);
+        var existingList = testShoppingList(household, plan);
+
+        var tomato = testIngredient(household, "Tomatoes", false);
+        var onion = testIngredient(household, "Onions", false);
+
+        // Existing list has both tomatoes and onions (generated)
+        var tomatoItem = testItem(existingList, tomato, new BigDecimal("2.00"), "pcs");
+        tomatoItem.setSourceRecipes(new UUID[]{UUID.randomUUID()});
+        existingList.getItems().add(tomatoItem);
+
+        var onionItem = testItem(existingList, onion, new BigDecimal("1.00"), "pcs");
+        onionItem.setSourceRecipes(new UUID[]{UUID.randomUUID()});
+        existingList.getItems().add(onionItem);
+
+        // New plan only has tomatoes — onions removed from recipes
+        var recipe = testRecipe(household, "Sauce");
+        recipe.getIngredients().add(new RecipeIngredient(recipe, tomato, new BigDecimal("3.00"), "pcs", (short) 1));
+        var slot = new WeekPlanSlot(plan, recipe, WEEK_START);
+        setId(slot, WeekPlanSlot.class, UUID.randomUUID());
+        plan.getSlots().add(slot);
+
+        when(weekPlanRepository.findById(plan.getId())).thenReturn(Optional.of(plan));
+        when(shoppingListRepository.findByHouseholdIdAndWeekPlanWeekStart(HOUSEHOLD_ID, WEEK_START))
+                .thenReturn(Optional.of(existingList));
+        when(shoppingListRepository.save(any(ShoppingList.class))).thenAnswer(i -> i.getArgument(0));
+        when(recipeRepository.findAllById(any())).thenReturn(List.of(recipe));
+
+        ShoppingListResponse result = shoppingService.generateFromPlan(HOUSEHOLD_ID, plan.getId());
+
+        assertThat(result.items()).hasSize(1);
+        assertThat(result.items().getFirst().name()).isEqualTo("Tomatoes");
+    }
+
+    // ── Source recipes deduplication ──
+
+    @Test
+    void generateFromPlanShouldDeduplicateSourceRecipesWhenSameRecipeInTwoSlots() {
+        var household = testHousehold();
+        var plan = testWeekPlan(household);
+        var recipe = testRecipe(household, "Pasta");
+        var tomato = testIngredient(household, "Tomatoes", false);
+        recipe.getIngredients().add(new RecipeIngredient(recipe, tomato, new BigDecimal("2.00"), "pcs", (short) 1));
+
+        // Same recipe in two slots
+        var slot1 = new WeekPlanSlot(plan, recipe, WEEK_START);
+        setId(slot1, WeekPlanSlot.class, UUID.randomUUID());
+        var slot2 = new WeekPlanSlot(plan, recipe, WEEK_START.plusDays(2));
+        setId(slot2, WeekPlanSlot.class, UUID.randomUUID());
+        plan.getSlots().add(slot1);
+        plan.getSlots().add(slot2);
+
+        when(weekPlanRepository.findById(plan.getId())).thenReturn(Optional.of(plan));
+        when(shoppingListRepository.findByHouseholdIdAndWeekPlanWeekStart(HOUSEHOLD_ID, WEEK_START))
+                .thenReturn(Optional.empty());
+        when(shoppingListRepository.save(any(ShoppingList.class))).thenAnswer(i -> {
+            ShoppingList sl = i.getArgument(0);
+            if (sl.getId() == null) setId(sl, ShoppingList.class, UUID.randomUUID());
+            return sl;
+        });
+        when(recipeRepository.findAllById(any())).thenReturn(List.of(recipe));
+
+        ShoppingListResponse result = shoppingService.generateFromPlan(HOUSEHOLD_ID, plan.getId());
+
+        assertThat(result.items()).hasSize(1);
+        assertThat(result.items().getFirst().sourceRecipes()).hasSize(1); // deduplicated
+    }
+
+    // ── checkItem household isolation ──
+
+    @Test
+    void checkItemShouldThrowWhenHouseholdMismatch() {
+        var otherHousehold = new Household("Other family", null);
+        setId(otherHousehold, Household.class, UUID.randomUUID());
+        var plan = new WeekPlan(otherHousehold, WEEK_START);
+        setId(plan, WeekPlan.class, UUID.randomUUID());
+        var list = new ShoppingList(otherHousehold, plan);
+        setId(list, ShoppingList.class, UUID.randomUUID());
+
+        when(shoppingListRepository.findById(list.getId())).thenReturn(Optional.of(list));
+
+        assertThatThrownBy(() -> shoppingService.checkItem(
+                HOUSEHOLD_ID, list.getId(), UUID.randomUUID(), new CheckItemRequest(true), UUID.randomUUID()))
+                .isInstanceOf(ResourceNotFoundException.class);
+    }
+
     // ── Generate from plan with empty slots ──
 
     @Test