feat(stock): add handling for unavailable variants in product selection

src/app/features/store/pages/store-home-page/store-home-page.component.html

@@ -30,6 +30,7 @@
         [items]="group.items"
         [loading]="isGroupLoading(group.id)"
         [loadImages]="!hasMainCarouselImages() || mainCarouselReady()"
+        [unavailableVariantIds]="unavailableVariantIds()"
         (buy)="onBuyProduct($event)"
         (addToCart)="onAddToCart($event)"
         (pageChange)="onPageChange(group.id, $event)"

src/app/features/store/pages/store-home-page/store-home-page.component.ts

@@ -18,7 +18,10 @@ import { CatalogFeaturedGroup } from '../../../../core/services/catalog/catalog.
 import { CatalogService } from '../../../../core/services/catalog/catalog.service';
 import { TenantService } from '../../../../core/services/tenant.service';
 import { ToastService } from '../../../../core/services/toast.service';
-import { CheckoutService } from '../../../../core/services/checkout.service';
+import {
+  CheckoutService,
+  isInsufficientStockResponse,
+} from '../../../../core/services/checkout.service';
 import {
   ProductListComponent,
   ProductListCartEvent,
@@ -60,6 +63,7 @@ export class StoreHomePageComponent implements OnInit, OnDestroy {
   protected readonly error = signal<string | null>(null);
   protected readonly mainCarouselReady = signal(false);
   protected readonly creatingDirectPurchase = signal(false);
+  protected readonly unavailableVariantIds = signal<ReadonlySet<number>>(new Set<number>());
   protected readonly mainCarouselImages = computed(() => this.tenant()?.extras?.carousel ?? []);
   protected readonly heroConfig = computed(() => this.tenant()?.extras?.heroConfig ?? null);
   protected readonly additionalInfo = computed(
@@ -200,6 +204,17 @@ export class StoreHomePageComponent implements OnInit, OnDestroy {
       await this.router.navigate(['/checkout'], { queryParams: { purchase: purchase.id } });
     } catch (error) {
       console.error('Failed to create direct purchase:', error);
+
+      if (error instanceof HttpErrorResponse && isInsufficientStockResponse(error.error)) {
+        const unavailableIds = error.error.unavailable_items
+          .map((item) => item.variant_id)
+          .filter((variantId): variantId is number => variantId !== null);
+
+        this.unavailableVariantIds.update((current) => new Set([...current, ...unavailableIds]));
+        this.toastService.danger(error.error.message);
+        return;
+      }
+
       this.toastService.danger('No se pudo iniciar la compra directa.');
     } finally {
       this.creatingDirectPurchase.set(false);