Senior Fullstack Engineer

About the project Xsolla ZK is building a cross-game infrastructure that empowers gamers to freely trade and use their digital assets without barriers. As a Fullstack Engineer, you'll work across the entire stack: Products: * Xsolla Bazaar — NFT marketplace for trading digital assets * Web3 Backpack — Smart wallet with account abstraction * Web3 SDKs — Developer toolkits for blockchain integration * Admin Panels — Internal tools for managing Web3 operations Tech Stack: Backend: * Language: Go (go-ethereum, ethkit) * Databases: MongoDB, PostgreSQL, Redis * API: REST, WebSocket, gRPC, OpenAPI (Swagger) * Message Queue: NATS, RabbitMQ, Kafka * Blockchain Infrastructure: * ZK Stack / ZKsync Era (EraVM, system contracts, native Account Abstraction) * Account Abstraction (ERC-4337): EntryPoint, UserOperation lifecycle, bundlers, paymasters * Ethereum L1 integration, abigen contract bindings Frontend: * Languages: JavaScript (ES6+), TypeScript * Frameworks: React, Next.js, React Native * State Management: RTK, Zustand * Styling: Tailwind CSS, Tamagui, CSS-in-JS * Web3 Libraries & Standards: * Wallet provider standards: EIP-1193, EIP-6963 (multi-wallet discovery), EIP-5792 (batched calls) * ethers.js, viem for Ethereum interactions * wagmi for React hooks * WalletConnect for multi-wallet support * Embedded/AA wallet SDK (e.g. Sequence, thirdweb, Privy, Dynamic, or equivalent) for social-login smart accounts Infrastructure: * DevOps: Docker, Kubernetes, GitLab CI/CD * Monitoring: Graylog, Prometheus Key Technical Challenges: * Full-Stack Web3 Features: Building end-to-end flows from smart contract events to real-time UI updates * Account Abstraction Integration: Implementing embedded/smart-account wallets with social auth, ERC-4337 UserOperation flows, and gasless transactions via paymasters * ZK Stack Backend: Working with EraVM differences, native Account Abstraction on zkSync-family chains, handling L1↔L2 bridging operations * Signature & Session Handling: Implementing EIP-712 signing, ERC-1271 verification, and session-key-scoped permissions for in-game transactions * Cross-Platform Consistency: Sharing business logic between web and mobile using React/React Native Responsibilities Backend Development: * Develop backend services in Go using go-ethereum/ethkit for wallet operations and blockchain interactions * Implement and monitor the ERC-4337 UserOperation lifecycle (prepare→sign→submit→confirm) against bundlers and paymasters * Implement smart contract interaction layer with abigen-generated Go bindings * Build Account Abstraction support: paymaster gas-sponsorship logic, session-key issuance (ERC-7710 / ERC-7715) for gameplay transactions * Design BFF services orchestrating data from multiple blockchain sources, indexers, and wallet infrastructure providers Frontend Development: * Build responsive applications using React/Next.js integrated with an embedded/AA wallet SDK * Implement Embedded Wallet flows: social auth (Google, Apple), email login, passkey (WebAuthn/P-256) support * Create Web3-enabled UIs using wagmi hooks and viem for contract reads/writes, following EIP-1193/EIP-6963 provider standards * Implement transaction confirmation flows that clearly convey what the player is approving (EIP-712 typed-data signing) * Develop real-time features with WebSocket subscriptions for blockchain events * Build cross-platform components with Tamagui for web and React Native Full-Stack Integration: * Design and implement complete features from smart contract events to UI updates * Handle ZK Stack specifics: EraVM gas model differences, native Account Abstraction, L1↔L2 bridging UI flows * Implement transaction tracking: status polling, reorg handling, user notifications * Create admin panels for managing NFT drops, marketplace settings, and analytics * Write comprehensive tests for both backend (Go) and frontend (Jest, React Testing Library) * Document APIs using OpenAPI/Swagger and maintain technical documentation Nice to Have Required: Backend Skills: * 3+ years of commercial experience with Go * Strong knowledge of REST API design and implementation * Experience with MongoDB and/or PostgreSQL * Understanding of microservices architecture Frontend Skills: * 3+ years of experience with React and modern JavaScript/TypeScript * Proficiency in state management solutions (Redux, Zustand, etc.) * Experience with responsive design and CSS frameworks * Understanding of web performance optimization General: * Experience with Git and CI/CD pipelines * Familiarity with Docker and containerization * Strong problem-solving and communication skills Preferred: Web3 & Blockchain: * Working knowledge of ERC-4337 Account Abstraction: EntryPoint, UserOperation lifecycle, bundler/paymaster roles * Understanding of session keys and delegated permissions (ERC-7710 / ERC-7715) and signature schemes (EIP-712, ERC-1271, WebAuthn/passkey) * Familiarity with wallet provider standards: EIP-1193, EIP-6963, EIP-5792 * Exposure to an embedded/AA wallet SDK (Sequence, thirdweb, Privy, Dynamic, Turnkey, or equivalent): * Embedded Wallet integration (social auth, passkeys) * Indexer/data-availability integration for balance/activity tracking * Gas-sponsorship / transaction-relay APIs * Knowledge of ZK Stack / ZKsync Era: * Understanding of EraVM vs EVM differences * L1↔L2 communication patterns * Native Account Abstraction on zkSync-family chains * Experience with ethers.js, viem, and wagmi for React * Understanding of smart contract interaction: ABI, events, transaction lifecycle * Knowledge of token standards (ERC-20, ERC-721, ERC-1155) Additional: * Experience with Next.js SSR/SSG and App Router * Familiarity with React Native and Tamagui for cross-platform * Understanding of WebSocket for real-time blockchain events * Knowledge of Kubernetes and cloud infrastructure