Senior Full Stack Engineer for SaaS Scaling

Senior engineers only. We’re staffing an engagement on an established multi-tenant B2B SaaS platform with live users. The work is scaling and hardening the system, not building greenfield features. Scope includes scaling a stateful Node.js/TypeScript app, improving queue-driven async architecture, handling real-time WebSocket fan-out under load, optimizing PostgreSQL performance, managing Redis caching and rate limiting, ensuring durable ingestion with zero data loss, and improving HA/failover, observability, and CI/CD. You’ll also help refactor a large codebase into enforceable module boundaries. You should have 6+ years of experience with production backend systems, proven work under real concurrency, and comfort working inside a large existing codebase. English is required. Full context will be shared after NDA. To apply, send: 1) one system you scaled with before/after numbers, 2) how you guarantee zero message loss and no duplicate processing during partial outages, and 3) your hourly rate and weekly availability.