nestjs-best-practices

# NestJS Best Practices ## Overview Grounded in the [Official NestJS Documentation](https://docs.nestjs.com/), this skill enforces modular architecture, dependency injection scoping, exception filters, DTO validation with `class-validator`, and Drizzle ORM integration patterns. ## When to Use - Designing/refactoring NestJS modules or dependency injection - Creating exception filters, validating DTOs, or integrating Drizzle ORM - Reviewing code for anti-patterns or onboarding to a NestJS codebase ## Instructions ### 1. Modular Architecture Follow strict module encapsulation. Each domain feature should be its own `@Module()`: - Export only what other modules need — keep internal providers private - Use `forwardRef()` only as a last resort for circular dependencies; prefer restructuring - Group related controllers, services, and repositories within the same module - Use a `SharedModule` for cross-cutting concerns (logging, configuration, caching) See `references/arch-module-boundaries.md` for enforcement rules. ### 2. Dependency Injection Choose the correct provider scope based on use case: | Scope | Lifecycle | Use Case | |-------------|------------------------------|---------------------------------------------| | `DEFAULT` | Singleton (shared) | Stateless services, repositories | | `REQUEST` | Per-request instance | Request-scoped data (tenant, user context) | | `TRANSIENT...