Senior Backend Engineer for Payment Ledger, Webhook Ingestion, and JIT Routing Core

We are looking for a senior backend engineer to help initialize a secure payment-routing backend foundation. The work involves setting up a clean backend scaffold, PostgreSQL transaction ledger, webhook ingestion layer, idempotency controls, and a high-speed authorization flow for payment/card-related events. This is not a simple CRUD API. The right developer should understand transaction safety, webhook retries, duplicate prevention, database row locks, secure secrets handling, and clean backend architecture. Primary responsibilities: * Initialize a clean backend foundation from an empty or near-empty repository * Build PostgreSQL ledger and reconciliation tables * Implement webhook intake, validation, and event persistence * Add idempotency and duplicate-processing protection * Prepare TypeScript/Node.js backend structure * Use Go where low-latency webhook or routing modules make sense * Work inside an approved cloud workspace only, without local source-code downloads * Keep credentials out of code and use secure environment/secret injection patterns Ideal candidate: * Senior backend engineer * Strong PostgreSQL and transaction-safety experience * Payment, fintech, ledger, banking, card, or webhook-heavy system experience preferred * Able to reason through ambiguous technical documents and identify blockers early * Can move quickly without overbuilding or making unsafe assumptions Please reply with: * Relevant backend/payment/webhook experience * Preferred stack for this type of work * Availability over the next 3-4 weeks * Any experience with PostgreSQL row-level locks, idempotency, Go modules, or secure cloud workspaces