Senior Full-Stack Engineer

About Hairball Hairball.io is an Inc. 5000 e-commerce integration consultancy with 550+ client relationships in the Shopify, NetSuite, and Celigo ecosystem. We are building a new AI-powered SaaS product for our market. Details about the product will be shared during the interview process. The Role We need a senior full-stack engineer to build the multi-tenant platform foundation for a new SaaS product over a 6-month contract engagement. You will be the primary architect and builder of the core infrastructure. A junior JavaScript developer on the team will work alongside you, learning the stack and eventually owning day-to-day development after your engagement ends. This is a founding-level role. You are not joining a team — you are building the platform that a team will grow around. The architecture decisions you make in the first 8 weeks will shape this product for years. What You Will Build Months 1-2: Platform Spine • Multi-tenant database schema with PostgreSQL Row-Level Security (RLS) enforcement on every tenant-scoped table • Authentication integration with Clerk, including multi-organization switching (one user, many tenants) • Role-based access control for six user roles with JSONB-based extensible permissions and ABAC extensions • API call logging pipeline with full attribution chain (tenant → service → execution → result) • Super Admin and Tenant Admin interfaces Months 3-4: Billing & Integrations • Stripe Billing integration: subscriptions, metered usage-based pricing, Customer Portal •External API integration pipeline with encrypted credential storage per tenant •Connection management UI for tenant-managed third-party credentials •Configuration inheritance system: platform defaults → tenant overrides → user preferences •Feature flag and module entitlement system for gating product capabilities per plan Months 5-6: Hardening & Handoff •Security hardening: immutable audit trails, environment separation (sandbox + production per tenant) •Performance optimization and production readiness review •Architecture Decision Records (ADRs) and documentation for the team inheriting the codebase •Code review and mentoring of the junior developer to ensure smooth transition Technology Stack Layer Technology Notes Framework Next.js 14 App Router + TypeScript Hosted on Vercel Database PostgreSQL 16+ (Neon) Drizzle ORM. RLS is non-negotiable. Cache / Queue Upstash Redis Job queuing, rate limiting Auth Clerk Multi-organization support required AI Anthropic Claude (primary) Multi-LLM gateway planned Billing Stripe Billing Subscriptions + usage-based metering CI/CD GitHub + Vercel Branch-based deploys, PR workflow Required Experience These are non-negotiable. If you have not done these things in production, this is not the right role. • Multi-tenant SaaS architecture: You have personally built (not just contributed to) a multi-tenant application with tenant data isolation. You understand the difference between application-level tenant filtering and database-level enforcement. PostgreSQL Row-Level Security: You have implemented RLS policies in production. You know how to set tenant context per transaction and test for cross-tenant data leakage. Next.js 14+ App Router: You are current with App Router (not Pages Router). You understand server components, server actions, route handlers, and middleware. TypeScript: You write TypeScript fluently, not JavaScript with type annotations bolted on. Stripe Billing integration: You have wired up subscriptions, handled webhooks with signature verification, and implemented metered/usage-based billing. Multi-org authentication: You have implemented multi-organization auth (Clerk, Auth0, or similar) in a SaaS product. You understand session scoping per organization. Strongly Preferred Experience with Drizzle ORM (or Prisma with willingness to learn Drizzle) AI/LLM application development — calling LLM APIs, streaming responses, token tracking Vercel deployment and optimization Experience mentoring junior developers Prior work in e-commerce, fintech, or financial data platforms What We Provide Complete architecture spec: A detailed specification covering every subsystem you will build. You are implementing a well-defined plan, not designing from scratch. Deep domain expertise: The product owner has deep expertise in the target market. You will never be guessing about business requirements. Working prototype: The backend pipeline and database schema already exist. You are building on a foundation, not from zero. AI development tooling: Claude Code is available as a pair programmer. The spec documents are structured for AI-assisted implementation. Autonomy: You make the technical decisions within architectural boundaries. No micromanagement. Weekly video check-in, daily async on Slack. How We Evaluate Step 1 — Portfolio review (async). Send links to multi-tenant SaaS products you have built. We want to see architecture decisions, not algorithm skills. Step 2 — Architecture conversation (60 min). We share the product spec and ask you to walk through how you would implement the multi-tenant isolation layer. We are looking for awareness of edge cases and honest assessment of complexity. Step 3 — Paid trial task (8-10 hours). Implement a specific piece of the platform against the actual codebase. Compensated at your hourly rate. Logistics Schedule: 30-35 hours/week, flexible. Overlap with US Eastern for 3-4 hours daily. Communication: Slack (daily async), weekly 30-minute video check-in, GitHub PRs for all code. Documentation: Every architectural decision gets a brief ADR in the repo. Payment: Biweekly invoicing, Net-15. Rate negotiable based on experience Location Remote Department Engineer/Developer Employment Type Contractor Minimum Experience Experienced