langchain-reference-architecture

# LangChain Reference Architecture ## Overview Production architectural patterns for LangChain: layered project structure, provider abstraction for vendor flexibility, chain registry for dynamic management, RAG architecture, and multi-agent orchestration. ## Layered Architecture ``` src/ ├── api/ # HTTP layer (Express/Fastify/FastAPI) │ ├── routes/ │ │ ├── chat.ts # POST /api/chat, /api/chat/stream │ │ └── documents.ts # POST /api/documents/ingest │ └── middleware/ │ ├── auth.ts # JWT/OAuth validation │ └── rateLimit.ts # Per-user rate limiting ├── core/ # Business logic (pure, testable) │ ├── chains/ │ │ ├── summarize.ts # Summarize chain factory │ │ ├── qa.ts # Q&A chain factory │ │ └── rag.ts # RAG chain factory │ ├── agents/ │ │ └── assistant.ts # Agent with tools │ └── tools/ │ ├── calculator.ts │ └── search.ts ├── infra/ # External integrations │ ├── llm/ │ │ └── factory.ts # LLM provider factory │ ├── vectorStore/ │ │ └── pinecone.ts # Vector store setup │ └── cache/ │ └── redis.ts # Response caching ├── config/ │ ├── index.ts # Config loader + validation │ └── models.ts # Model configurations └── index.ts # App entry point ``` ## Provider Abstraction (LLM Factory) ```typescript // src/infra/llm/factory.ts import { ChatOpenAI } from...