Self-hostable enterprise feature flag service with real-time flag propagation via SSE + Redis Pub/Sub — eliminating per-request network round-trips to the flag server. Built with Fastify, PostgreSQL/Drizzle, Redis, and Turborepo. Features a custom recursive rule engine, consistent hashing for sticky rollouts, and optimistic locking for conflict-safe concurrent edits. Shipped a TypeScript SDK with three-tier fallback logic, a Next.js management dashboard with two-level RBAC, and a Fumadocs documentation site. Tech: TypeScript · Fastify · PostgreSQL · Redis · SSE · Docker · Turborepo