Crypto Custody & Game Platform Developer

We have a fully built, tested platform and need an experienced backend + blockchain engineer to take it across the last mile to a live mainnet launch. This is not a greenfield build — the code is done and passing tests. The work is provisioning production infrastructure, validating every on-chain path on testnet, hardening the operational layer, and supporting an independent security audit before we handle real customer funds. This is a custodial, real-money crypto product. Apply only if you've shipped (or audited) systems that move real money on-chain and you're comfortable with that responsibility. What's already built Node.js / Express backend, SQLite (better-sqlite3), ~108 passing tests Custodial HD wallet (BIP-39): per-user deposit addresses + hot/cold separation, built on ethers v6 Multi-chain EVM support — Ethereum, Polygon, BSC, Arbitrum — for USDT & USDC (ERC-20) Deposit watcher, cold-storage sweeper, and a tiered withdrawal service (auto/manual approval, nonce-locked signing, stuck-tx rebroadcast) Double-entry ledger in integer micro-units (no floats in any balance math) Real-time game engine with WebSocket delivery and a price oracle, plus pool-scaling exposure/solvency caps Full affiliate program (referral tracking, period-locked monthly commissions, on-chain payouts) Admin dashboard, player app, and affiliate portal Complete .env-driven config and a written go-live checklist What we need done Provision production infra: RPC nodes (own or provider) for all four chains, secret management for the hot-wallet seed (KMS/HSM/secret store), TLS, hosting Verify token contract addresses/decimals against explorers; fund and monitor hot-wallet gas End-to-end testnet validation of every on-chain path: deposit → credit → withdraw → sweep → affiliate payout Coordinate and support an independent third-party security audit (custody, withdrawal/sweep signing, ledger, settlement pricing) and remediate findings Build the operational layer: monitoring/alerting, hot-float top-up automation, rate limiting, automated backups, runbooks Live calibration of the game's pricing curve from realized volatility Mainnet cutover and smoke testing Required skills Strong production Node.js / Express Production EVM/blockchain engineering with ethers.js v6: ERC-20 transfers, gas & nonce management, transaction lifecycle, confirmations/reorg handling Custodial key management & wallet security — HD wallets, hot/cold design, secret stores / KMS / HSM Hands-on experience building or auditing crypto deposit/withdrawal systems SQL/SQLite and a solid grasp of double-entry accounting DevOps: Linux, process/secret management, monitoring, TLS, backups Genuine security mindset; comfortable working through (or alongside) a formal audit Nice to have iGaming / real-money gaming or crash-game experience WebSocket real-time systems at scale Prior launch of a custodial crypto product To apply, please include: A short description of a custodial crypto deposit/withdrawal or wallet system you've taken to production — your role, the chains, and how you handled key security and transaction reliability. How you'd approach end-to-end testnet validation of deposit → withdraw → sweep before mainnet. Confirmation you're comfortable on a real-money platform, and your availability. Start your proposal with the word "[choose a keyword, e.g. LEDGER]" so we know you read this.