Beyond Auto-Generated Apps. Production-Grade Software.

Build a SaaS dashboard with user authentication, billing management, and usage analytics. Use React and Node.js.

You are a senior full-stack architect building production SaaS applications.

Build a user dashboard for: [Next.js App Router / Express + React]
- Auth: [Auth.js / Clerk / Supabase Auth] with RBAC (admin/member/viewer)
- Database: [PostgreSQL / MySQL] with Prisma ORM
- Billing: Stripe integration with webhook handling

Requirements:
1. Auth middleware: session validation, CSRF protection, rate limiting (100 req/min)
2. Dashboard layout: collapsible sidebar, breadcrumbs, responsive grid (mobile: stacked)
3. Usage analytics: time-series chart with date range picker, export CSV
4. Billing page: current plan, usage meter, upgrade/downgrade flow, invoice history
5. Role-based UI: conditionally render admin controls, hide billing from viewers
6. Loading states: skeleton screens matching final layout dimensions
7. Error boundaries: per-widget isolation, retry buttons, error reporting
8. Optimistic updates for settings changes with rollback on failure

Security: parameterized queries, helmet headers, CORS whitelist, input sanitization via Zod.
Performance: React.lazy per route, stale-while-revalidate for analytics, connection pooling.

Create a REST API with user registration, login, and CRUD operations for a blog. Include JWT authentication.

You are a senior backend engineer building production REST APIs.

Create an authenticated CRUD API for: [Express / Fastify / Hono]
- Database: [PostgreSQL + Prisma / MongoDB + Mongoose]
- Auth: JWT with refresh token rotation

Endpoints:
1. POST /auth/register — email validation, password hash (bcrypt, 12 rounds), welcome email
2. POST /auth/login — rate limited (5 attempts/15min), returns access + refresh tokens
3. POST /auth/refresh — rotate refresh token, invalidate old token
4. GET /posts — paginated (cursor-based), filterable by author/tag, cached (60s TTL)
5. POST /posts — auth required, Zod body validation, slug auto-generation
6. PUT /posts/:id — ownership check, optimistic locking via version field
7. DELETE /posts/:id — soft delete with 30-day retention

Middleware stack: cors, helmet, compression, request-id, morgan logging, error handler.
Error format: { error: { code, message, details? } } with appropriate HTTP status codes.
Tests: Jest + Supertest — happy path + auth failures + validation errors + edge cases.
Docs: OpenAPI 3.1 spec auto-generated from Zod schemas.

Build a real-time chat app with rooms, user presence, and message history. Use WebSockets.

You are a senior real-time systems engineer building production chat applications.

Build a real-time chat system for: [Next.js + Socket.io / Express + ws]
- Database: [PostgreSQL / Redis] for message persistence
- Auth: [JWT / session-based] with WebSocket auth handshake

Requirements:
1. Room management: create/join/leave rooms, room list with member counts
2. WebSocket auth: validate token on connection, reject expired sessions
3. Message delivery: at-least-once guarantee, client-side deduplication by message ID
4. Presence system: online/offline/typing indicators with 30s heartbeat
5. Message history: cursor-based pagination (50 messages/page), lazy load on scroll-up
6. Rate limiting: 10 messages/second per user, exponential backoff on limit
7. Reconnection: auto-reconnect with backoff (1s, 2s, 4s, max 30s), message gap sync
8. Optimistic UI: show sent message immediately, mark as delivered on server ack

Accessibility: ARIA live region for new messages, keyboard navigation between rooms, screen reader announcements for presence changes.
Scalability: Redis pub/sub for horizontal scaling, connection pooling, graceful shutdown drain.
Edge cases: handle duplicate tabs, stale connections, message ordering on reconnect.