Apply the waste-disposal charge

Appends the charge line — quantity 1 at the previewed amount, unit lav, the company's default VAT rate (its first enabled one), last position — recomputes the totals and returns the updated document (as the line-items batch does).

The rules are re-checked server-side and the line is written in one transaction holding the document's row lock, so concurrent calls run one after the other and add the line once. When the charge can't be applied the response is 409 waste_disposal_not_applicable with error.reason (disabled, already_applied, nothing_to_charge, and on worksheets fully_paid).