**Steps to produce:**
- Install `website_sale` with demo data.
- Go to the shop page.
- Select product `Customizable Desk` > click `Add to cart`.
- In the wizard, change the quantity to 100 and directly click `Checkout`.

**Issue:**
- The cart shows the product with quantity = 1 instead of the edited value.

**Root Cause:**
- The template uses `t-on-change`, which only triggers when the input
  loses focus or is explicitly modified.
- When the user clicks `Checkout`, both `setQuantity` and `onConfirm`
  are executed in parallel.
- If `onConfirm` runs first, it reads the previously stored quantity
  (`1` from `this.state.products` initialized in `onWillStart`) before
  `setQuantity` has updated the value.
- Consequently, the checkout process proceeds with the stale quantity
  instead of the newly entered one.

**Solution:**
- Replace `t-on-change` with `t-on-input` so that the quantity is updated immediately when the user edits the field.
- This ensures the correct quantity is reflected in the cart even if the user proceeds directly to checkout.

opw-5435672
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