Polish National e-Invoice System (KSeF) accounting assistant (English). Use when working with KSeF 2.0 API, FA(3) invoices, Polish VAT compliance, e-invoice processing, payment matching, VAT registers (JPK_V7), corrective invoices, split payment mechanism (MPP), or Polish accounting workflows. Provides domain knowledge for invoice issuance, purchase processing, cost classification, fraud detection, and cash flow forecasting in the KSeF ecosystem.