Offline-first PWA that runs a furniture showroom and its workshop end to end — quotes to installments to payroll

An Arabic-first (RTL) management system for furniture showrooms that also manufacture their own pieces: purchase invoices for raw materials, sales invoices with installment plans, a live inventory, customer and supplier debts, worker advances and monthly payroll, expenses, account statements and full reports — all in one device. The tricky part was the data model, not the screens. Stock is an append-only ledger, never an editable number, so every movement has an effect that can be reversed when an invoice is voided. Money is stored as integer piasters, so totals never drift from floating-point rounding. Voiding, editing, restoring a backup and running payroll each happen inside a single IndexedDB transaction. It ships as an installable PWA that works with no connection at all after the first load, because showroom Wi-Fi is unreliable. A versioned, checksummed JSON backup replaces the whole database in one transaction, and the repository layer is separated from the screens so the same UI can move to Neon/Postgres later without a rewrite.