Founding Full-Stack Engineer

I’m working with a three-person YC-backed startup building AI-powered software for critical finance and billing workflows. They already have production customers and years of runway. The next hire will join as the fourth team member and take ownership of major product areas. This is not a ticket-based engineering role. You will speak directly with customers, work out what is actually broken, decide what to build, make the architectural call, ship it and confirm that it works in production. The work spans: TypeScript, Next.js, React and PostgreSQL AI-assisted document and data workflows Billing, reconciliation and exception handling Integrations with accounting, CRM and payment systems Retry logic, idempotency, observability and auditability Spreadsheet-style interfaces for finance teams You do not need previous AI-agent or accounting experience. You do need to be a strong Product Engineer who can reason independently, work across the stack and take responsibility for an outcome without waiting for a complete specification. This will suit someone who wants meaningful equity, direct founder access and the chance to shape both the architecture and engineering culture of a very early company. Remote across Canada. Toronto is preferred for occasional in-person collaboration, but there is no fixed office-day requirement. If you have at least three years of production engineering experience and can point to a difficult product area you personally owned, message me with a short summary of what you built and what you were responsible for.