Better Auth expert for Next.js App Router and Node/TypeScript projects. Use when implementing authentication/authorization with Better Auth for: (1) creating the Better Auth instance (providers, plugins, security options), (2) wiring Next.js route handlers (`/api/auth/[...all]`), (3) reading sessions in Server Components/Route Handlers, (4) protecting routes via middleware (cookie-only or full session validation with Node runtime), (5) using database adapters (especially Prisma) and schema setup, and (6) troubleshooting cookies/CSRF/trusted origins/baseURL and callback URL issues.