Squashed commit of the following:

commit 1dc4e29c69
Author: ncoronel <ncoronel@quo.ar>
Date:   Wed Aug 19 13:58:03 2026 -0300

    refactor(reservations): unify expiration command

commit 093e894cc3
Author: ncoronel <ncoronel@quo.ar>
Date:   Wed Aug 19 13:48:09 2026 -0300

    feat(cart): expire abandoned stock reservations

commit fdf0f3328f
Author: ncoronel <ncoronel@quo.ar>
Date:   Wed Aug 19 12:53:12 2026 -0300

    refactor(stock): implement expiration for stock reservations and add configuration

commit 8d6bcdcc43
Author: ncoronel <ncoronel@quo.ar>
Date:   Wed Aug 19 12:38:21 2026 -0300

    refactor(cart): invalidate payment on actual changes

commit 3206e293eb
Author: ncoronel <ncoronel@quo.ar>
Date:   Wed Aug 19 12:24:48 2026 -0300

    refactor(cart): own checkout item editing

commit aed99bd05e
Author: ncoronel <ncoronel@quo.ar>
Date:   Wed Aug 19 12:14:57 2026 -0300

    refactor(checkout): remove legacy purchase item reservations

commit f1649e0e4b
Author: ncoronel <ncoronel@quo.ar>
Date:   Wed Aug 19 12:06:29 2026 -0300

    refactor(checkout): materialize purchase items on confirmation

commit e6c4b40a37
Author: ncoronel <ncoronel@quo.ar>
Date:   Wed Aug 19 12:06:19 2026 -0300

    feat(inventory): add traceable cart stock reservations

app/Domains/Cart/Services/CartService.php

@@ -4,15 +4,24 @@ namespace App\Domains\Cart\Services;
 
 use App\Domains\Auth\Models\User;
 use App\Domains\Cart\Models\Cart;
+use App\Domains\Cart\Models\CartItem;
+use App\Domains\Catalog\Services\StockReservationService;
+use App\Domains\Purchase\Models\Purchase;
 use App\Domains\Tenant\Models\Tenant;
 use Illuminate\Http\Request;
 use Illuminate\Support\Facades\Auth;
+use Illuminate\Support\Facades\DB;
 use Illuminate\Support\Str;
+use Illuminate\Validation\ValidationException;
 use Symfony\Component\HttpFoundation\Cookie;
 use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
 
 class CartService
 {
+    public function __construct(
+        private readonly StockReservationService $reservations,
+    ) {}
+
     public function show(Tenant $tenant, Request $request): Cart
     {
         $resolvedIdentity = $this->resolveIdentity($request);
@@ -66,6 +75,107 @@ class CartService
         return $this->loadCart($cart);
     }
 
+    public function updateCheckoutItem(
+        Tenant $tenant,
+        Request $request,
+        Cart $cart,
+        int $cartItemId,
+        int $quantity,
+        ?int $variantId,
+        bool $updateVariant,
+    ): Cart {
+        $user = $request->user() ?? Auth::guard('sanctum')->user();
+
+        if (! $user instanceof User) {
+            throw new NotFoundHttpException('Checkout cart not found.');
+        }
+
+        return DB::transaction(function () use (
+            $tenant,
+            $user,
+            $cart,
+            $cartItemId,
+            $quantity,
+            $variantId,
+            $updateVariant,
+        ): Cart {
+            /** @var Purchase|null $purchase */
+            $purchase = Purchase::query()
+                ->where('cart_id', $cart->getKey())
+                ->where('tenant_codigo', $tenant->codigo)
+                ->where('user_id', $user->getKey())
+                ->whereIn('status', [
+                    Purchase::STATUS_CREATED,
+                    Purchase::STATUS_PENDING_PAYMENT,
+                ])
+                ->whereDoesntHave('items')
+                ->lockForUpdate()
+                ->first();
+
+            if ($purchase === null) {
+                throw new NotFoundHttpException('Checkout cart not found.');
+            }
+
+            if ($purchase->expires_at !== null && $purchase->expires_at->isPast()) {
+                throw ValidationException::withMessages([
+                    'cart' => __('api.purchase.not_editable'),
+                ]);
+            }
+
+            /** @var Cart|null $checkoutCart */
+            $checkoutCart = Cart::query()
+                ->whereKey($cart->getKey())
+                ->where('tenant_codigo', $tenant->codigo)
+                ->where('user_id', $user->getKey())
+                ->where('status', 'checkout')
+                ->lockForUpdate()
+                ->first();
+
+            if ($checkoutCart === null) {
+                throw new NotFoundHttpException('Checkout cart not found.');
+            }
+
+            /** @var CartItem|null $cartItem */
+            $cartItem = $checkoutCart->items()
+                ->whereKey($cartItemId)
+                ->lockForUpdate()
+                ->first();
+
+            if ($cartItem === null) {
+                throw new NotFoundHttpException('Checkout item not found.');
+            }
+
+            $hasChanges = (int) $cartItem->cantidad !== $quantity
+                || ($updateVariant && $cartItem->variant_id !== $variantId);
+
+            if (! $hasChanges) {
+                return $this->loadCart($checkoutCart);
+            }
+
+            $checkoutCart->updateItem(
+                $cartItemId,
+                $quantity,
+                $variantId,
+                $updateVariant,
+                $purchase->getKey(),
+            );
+
+            $purchase->telepagosQr()->delete();
+            $purchase->update([
+                'status' => Purchase::STATUS_CREATED,
+                'payment_method' => null,
+                'transfer_payer_dni' => null,
+                'total' => $checkoutCart->getTotalAmount(),
+                'expires_at' => now()->addMinutes(
+                    max(1, (int) config('purchase.checkout_expiration_minutes', 30)),
+                ),
+            ]);
+            $this->reservations->syncPurchaseExpiration($purchase);
+
+            return $this->loadCart($checkoutCart);
+        });
+    }
+
     public function removeItem(Tenant $tenant, Request $request, int $cartItemId): Cart
     {
         $identity = $this->requireIdentity($request);