feat(cart): prevent automatic variant replacement and handle selection errors

src/app/shared/components/cart-item/cart-item.component.html

@@ -31,8 +31,9 @@
         class="cart-item-variant-selector"
         [variants]="variants()"
         [selectedVariant]="selectedVariant()"
+        [autoSelectFirst]="false"
         [compact]="true"
-        (selectedVariantChange)="onVariantChange($event)"
+        (selectionValuesChange)="onVariantChange($event.selectedVariant)"
       />
     } @else {
       <div class="d-grid cart-item-attributes">

src/app/shared/components/cart/cart.component.spec.ts

@@ -3,13 +3,14 @@ import { signal } from '@angular/core';
 import { TestBed, getTestBed } from '@angular/core/testing';
 import { By } from '@angular/platform-browser';
 import { BrowserTestingModule, platformBrowserTesting } from '@angular/platform-browser/testing';
-import { of, throwError } from 'rxjs';
+import { of, Subject, throwError } from 'rxjs';
 import { afterEach, beforeAll, describe, expect, it, vi } from 'vitest';
 
 import { CartService } from '../../../core/services/cart/cart.service';
 import { ModalService } from '../../../core/services/modal.service';
 import { ToastService } from '../../../core/services/toast.service';
 import { CartComponent } from './cart.component';
+import { VariantSelectorComponent } from '../variant-selector/variant-selector.component';
 
 describe('CartComponent', () => {
   beforeAll(() => {
@@ -22,6 +23,7 @@ describe('CartComponent', () => {
 
   afterEach(() => {
     TestBed.resetTestingModule();
+    vi.restoreAllMocks();
   });
 
   it('shows an empty cart message when there are no items', async () => {
@@ -565,6 +567,57 @@ describe('CartComponent', () => {
     expect(quantityChange).not.toHaveBeenCalled();
   });
 
+  it('does not automatically replace an unavailable variant or retry a rejected selection', async () => {
+    const response = new Subject<unknown>();
+    const updateItemVariant = vi.fn().mockReturnValue(response);
+    const danger = vi.fn();
+    vi.spyOn(console, 'error').mockImplementation(() => {});
+    await TestBed.configureTestingModule({
+      imports: [CartComponent],
+      providers: [
+        { provide: CartService, useValue: { cart: signal(null), updateItemVariant } },
+        { provide: ModalService, useValue: {} },
+        { provide: ToastService, useValue: { success: vi.fn(), danger } },
+      ],
+    }).compileComponents();
+    const fixture = TestBed.createComponent(CartComponent);
+    const item = {
+      cartItemId: 10,
+      imageUrl: null,
+      product: 'Entrada',
+      originalPrice: null,
+      discountedPrice: 1000,
+      discountPercentage: null,
+      attributes: [],
+      quantity: 2,
+      variantId: 20,
+      variants: [{ id: 20, values: { fecha: '09/10' } }],
+    };
+    fixture.componentRef.setInput('items', [item]);
+    fixture.detectChanges();
+
+    const rescheduledItem = {
+      ...item, variants: [{ id: 21, values: { fecha: '20/10' } }],
+    };
+    fixture.componentRef.setInput('items', [rescheduledItem]);
+    fixture.detectChanges();
+    expect(updateItemVariant).not.toHaveBeenCalled();
+
+    const selector = fixture.debugElement.query(By.directive(VariantSelectorComponent));
+    (selector.componentInstance as any).onValueChange('fecha', '20/10');
+    fixture.detectChanges();
+    expect(updateItemVariant).toHaveBeenCalledExactlyOnceWith(10, 2, 21);
+
+    response.error({ status: 422, error: { message: 'Variante no disponible.' } });
+    fixture.detectChanges();
+    fixture.componentRef.setInput('items', [{
+      ...rescheduledItem, variants: [...rescheduledItem.variants],
+    }]);
+    fixture.detectChanges();
+    expect(updateItemVariant).toHaveBeenCalledTimes(1);
+    expect(danger).toHaveBeenCalledOnce();
+  });
+
   it('persists a variant selected from a cart row', async () => {
     const updateItemVariant = vi.fn().mockReturnValue(
       of({