Bun AWS Lambda (Clean Architecture)

Handler Pattern - Thin Adapter

Lambda handlers are thin adapters that:

1. Initialize DI Container (cold start)
2. Parse input
3. Resolve Use Case from DI
4. Execute and return result
5. Map domain exceptions to HTTP status

// src/functions/create-category.ts
import type { APIGatewayProxyEventV2, APIGatewayProxyResultV2 } from 'aws-lambda'
import { DIContainer, TOKENS, initializeDI } from '@/backend/di'
import type { CreateCategoryUseCase } from '@/backend/application/category/use-cases'
import { DomainException, NotFoundException } from '@/backend/domain/shared/exceptions'

let initialized = false