Senior Full Stack Engineer - Upgrade Existing NFT Marketplace to Production-Ready Application

_Project Overview We are looking for an experienced Senior Full-Stack Web3 Engineer to upgrade our existing NFT marketplace, CryptoKet, into a reliable, secure, scalable, and production-ready application. The project already has an initial implementation that includes a Next.js frontend, Solidity-based NFT marketplace smart contract, Ethereum wallet integration, IPFS metadata storage, NFT minting, marketplace listings, purchases, and resale functionality. However, the current application needs architectural improvements, backend development, blockchain data synchronization, performance optimization, security reviews, automated testing, and deployment preparation. The selected engineer will be responsible for reviewing the existing source code, identifying technical limitations, proposing a practical upgrade plan, and implementing the agreed improvements without unnecessarily rebuilding working components. We are looking for an engineer who understands the entire Web3 application lifecycle, from frontend interfaces and backend APIs to smart contract interactions, blockchain indexing, data consistency, and production deployment. _Existing Technology Stack Frontend: Next.js 12, React 17, Tailwind CSS Smart contracts: Solidity 0.8.4 and ERC-721 Development framework: Hardhat Blockchain integration: ethers.js 5 and Web3Modal 1 NFT metadata and storage: IPFS Existing functionality: Wallet connection, NFT creation, listing, purchasing, and resale The current configuration targets Ethereum Sepolia. The engineer must verify the deployed contract, current network configuration, and existing functionality before recommending a production network or contract migration. The selected engineer may recommend updated libraries, a modern frontend architecture, a separate backend service, and additional infrastructure when justified by the project's requirements.