WooCommerce’s block-based cart and checkout do not run the classic woocommerce_check_cart_items path. They validate through the Store API. A quantity plugin written before the blocks — or one that never caught up — will pass every classic test and still let an invalid quantity through the block cart.
What to check
- Does the plugin mention the Store API or “block cart” explicitly? If not, assume it is unprotected.
- Test with the block cart and block checkout enabled, not just the shortcode pages.
- Check that native block quantity constraints (minimum / maximum / multiple-of) are set — the stepper itself should refuse invalid values.
Warning: Many stores switched to the block cart in the last two WooCommerce releases without re-testing their quantity rules. It is worth a five-minute check.
Quantity Manager wires into the Store API and the native block quantity constraints, so the block cart enforces the same rules as everything else.