backend-dev-guidelineslisted

# Backend Development Guidelines ## Purpose Establish consistency and best practices across Langfuse's backend packages (web, worker, packages/shared) using Next.js 14, tRPC, BullMQ, and TypeScript patterns. ## When to Use This Skill Automatically activates when working on: - Creating or modifying tRPC routers and procedures - Creating or modifying public API endpoints (REST) - Creating or modifying BullMQ queue consumers and producers - Building services with business logic - Authenticating API requests - Accessing resources based on entitlements - Implementing middleware (tRPC, NextAuth, public API) - Database operations with Prisma (PostgreSQL) or ClickHouse - Observability with OpenTelemetry, DataDog, logger, and traceException - Input validation with Zod v4 - Environment configuration from env variables - Backend testing and refactoring --- ## Quick Start ### UI: New tRPC Feature Checklist (Web) - [ ] **Router**: Define in `features/[feature]/server/*Router.ts` - [ ] **Procedures**: Use appropriate procedure type (protected, public) - [ ] **Authentication**: Use JWT authorization via middlewares. - [ ] **Entitlement check**: Access resources based on resource and role - [ ] **Validation**: Zod v4 schema for input - [ ] **Service**: Business logic in service file - [ ] **Error handling**: Use traceException wrapper - [ ] **Tests**: Unit + integration tests in `__tests__/` - [ ] **Config**: Access via env.mjs ### SDKs: New Public API Endpoint Checklist (Web) - [