Prevent oversell by conditioning stock updates and locking SKUs in primary-key order, and record the same concurrent-counter rule in the API spec and agent guide.
Co-authored-by: Cursor <cursoragent@cursor.com>
Keep the REST contract; move domain logic out of route files so checkout, fulfillment, and identity can be reused across customer, shop, and admin surfaces.
Co-authored-by: Cursor <cursoragent@cursor.com>