Use the business-file-assistant skill. Work only in examples/billing-check/input and write new results in examples/billing-check/output. Do not read expected files. Compare work.csv with invoice.csv by work_id. Only completed work is billable; expected amount is hours times rate_php, without tax. Write result.json with currency, completed_work_total, invoice_total and issues. Each issue needs kind, work_id and line_ids; include expected_amount/billed_amount for an amount mismatch. Use duplicate_work, amount_mismatch, not_completed, unknown_work or missing_invoice. Calculate using local tools and retain the calculation script.
