Fix detached instance errors in physical product handling test

The test was failing due to SQLAlchemy DetachedInstanceError when
accessing object properties after transaction.manager.commit().

Changes:
- Save cart and shop UUIDs before commit to avoid detached access
- Re-query cart from database after commit using get_cart_by_id
- Pass shop_id parameter in cart URL to properly set request.shop
- Use saved UUID variables instead of accessing detached objects

This ensures request.shop_location is correctly resolved so the
handling options (local pickup, delivery, shipping) render properly
in the cart template.

All 357 tests now pass including the physical product handling test.

make_post_sell/tests/test_physical_product_handling.py

@@ -139,15 +139,25 @@ class PhysicalProductHandlingTests(unittest.TestCase):
         self.dbsession.add(cart)
         self.dbsession.flush()
 
+        # Save IDs before commit
+        cart_id = cart.id
+        cart_uuid_str = cart.uuid_str
+        shop_uuid_str = shop.uuid_str
+
         # Commit transaction
         transaction.manager.commit()
 
+        # Re-query cart to avoid detached instance error
+        from ..models.cart import get_cart_by_id
+        cart = get_cart_by_id(self.dbsession, cart_id)
+
         # Verify cart has physical products
         self.assertEqual(cart.count, 1)
         self.assertTrue(len(cart.physical_products) > 0, "Cart should have physical products")
 
         # 5. Get cart page and verify handling options section appears
-        cart_res = self.testapp.get(f"/cart/{cart.id}")
+        # Need to pass shop_id so request.shop is set correctly
+        cart_res = self.testapp.get(f"/cart/{cart_id}?shop_id={shop_uuid_str}")
         cart_body = cart_res.body.decode()
 
         # Verify handling options form is present
@@ -156,10 +166,10 @@ class PhysicalProductHandlingTests(unittest.TestCase):
 
         # 6. Submit handling option form with CSRF token
         # This is the critical test - the form MUST include CSRF token
-        csrf_token = self.get_csrf_token(shop.uuid_str)
+        csrf_token = self.get_csrf_token(shop_uuid_str)
 
         handling_res = self.testapp.post(
-            f"/cart/{cart.uuid_str}/handling-option",
+            f"/cart/{cart_uuid_str}/handling-option",
             {
                 "handling_option": "local_pickup",
                 "csrf_token": csrf_token,
@@ -188,9 +198,9 @@ class PhysicalProductHandlingTests(unittest.TestCase):
             ("local_shipping", 750),
             ("international_shipping", 1500),
         ]:
-            csrf_token = self.get_csrf_token(shop.uuid_str)
+            csrf_token = self.get_csrf_token(shop_uuid_str)
             res = self.testapp.post(
-                f"/cart/{cart.uuid_str}/handling-option",
+                f"/cart/{cart_uuid_str}/handling-option",
                 {
                     "handling_option": option,
                     "csrf_token": csrf_token,