Laravel Ecommerce Tutorial: Cart, Orders, No Overselling

Two buyers click "Pay" on the last unit in stock, and a checkout that reads the stock, checks it in PHP and writes it back sells it to both. This tutorial builds a Laravel 12 cart, checkout and order pipeline in Docker with integer money, idempotent order creation, queued confirmation emails, and a concurrent test that fails if you remove the stock protection.

The payoff is the measured race table, run on one laptop on 2026-10-07: 40 processes racing for 10 units produced 40 orders with the naive checkout, and exactly 10 orders (30 refused) with either fix.

Versions: Laravel 12.69.3 (php artisan --version prints Laravel Framework 12.69.3), PHP 8.4.26, MySQL 8.0.46, Docker 29.7.2, stripe-mock 0.206.0. The Stripe part ran against stripe-mock, not the live API.

What most Laravel shopping cart tutorials skip

Tutorials such as the phppot walkthrough, Educative's checkout lesson and Codecourse's series build a session cart, an OrderController and Stripe, which works for one buyer at a time. They don't answer:

1. Two requests, one unit left: who wins?
2. The browser retries a checkout POST: do you get two orders?
3. Is 19.99 * 3 safe to store?
4. Does the confirmation email go out for an order that rolled back?

Set up the Laravel lab with Docker

Commands I used (Git Bash on Windows; any Docker host works). The shoplab-php image is this Dockerfile:

FROM php:8.