Senior Full-Stack Engineer Needed For AI-Powered SaaS Platform (Long-Term)

I am looking for a senior full-stack engineer to join us as a long-term technical partner on an AI-powered SaaS platform currently in active development. This is not a task-by-task engagement. We want someone who takes full ownership of the product, thinks ahead of the requirements, and builds things that hold up in production under real usage. About the product: We are building a multi-tenant B2B platform with AI-assisted workflows, subscription billing, and role-based access across multiple user types. The platform processes documents, generates AI-powered outputs, and integrates with third-party services including payment providers and communication tools. We have an existing codebase and documentation. You will be taking over as the primary technical decision-maker. What you will own: Backend architecture and API design using Node.js and NestJS. Database modeling and migrations in PostgreSQL with proper multi-tenant isolation and row-level security. Authentication and role-based access control across multiple user types. AI integration using OpenAI and Anthropic APIs inside real business logic, not chat wrappers. Background job processing for document and data workflows. Payment integration including subscription lifecycle, webhook handling, and billing edge cases. Frontend implementation in Next.js and React with TypeScript. AWS infrastructure including EC2, S3, RDS, and Lambda. CI/CD pipelines with GitHub Actions and Docker. Mobile support via React Native when needed. What we need from you: Someone who reads the brief and identifies the ambiguities before coding rather than after. Someone who tests normal cases, edge cases, degraded states, and unauthorized access paths without being asked. Someone who has built in fintech or regulated environments and understands what compliance-sensitive systems actually require. Someone who started building before AI was part of the stack and uses AI tools intelligently on top of a solid foundation. Strong preference for: Experience in fintech, payment processing, or regulated environments with audit trail requirements. Experience building multi-tenant platforms where data isolation between tenants is enforced at the database layer. Experience taking a product from zero to production and continuing to own it after launch. Experience with document processing, OCR, or AI-powered data extraction pipelines. What we are not looking for: Someone who needs detailed specs for every decision and treats AI tools as a substitute for engineering judgment. Engagement: This is a long-term role. We are looking for one technical partner who is fully inside the product. To apply, please include: 1. A brief description of a multi-tenant SaaS platform you have built or contributed to significantly. 2. Your experience with payment integrations including any edge cases you have had to solve. 3. ⁠One example of a production bug or architectural decision that required you to think beyond the immediate task. 4. ⁠Your hourly rate and availability.