Can Zen Cart shopping cart "reserve" store items for fixed amount of time?

[Hermitian]

.Product status was changed to 0, quantity is -1.

Decrement needs to fail if inventory is zero, and return a failure code as well.

[balihr]

Decrement needs to fail if inventory is zero, and return a failure code as well.

It usually does and if customer_2 was on any other page except checkout_confirmation (final step before placing the order), they'd be redirected to the shopping_cart page with a notice the product is currently out of stock. IMO, it's just the existing stock check logic that should be added to the checkout_process module that runs just before the order is created.

[Hermitian]

20 years ago I wrote an entire store from scratch in Perl + SQL. I just don't have time to do it again and maintain it in PHP.

[Hermitian]

There are a lot of checks

As you're probably aware, checks aren't enough. You need SQL or some other gateway to negotiate access to the inventory data.