Build production LangChain agents with create_agent(), tools, and middleware patterns.

• ›Use create_agent() with model, tools list, and system prompt; configure state persistence with checkpointer and thread_id for conversation memory across invocations
• ›Define tools via @tool decorator (Python) or tool() function (TypeScript) with clear descriptions so agents know when to call them
• ›Add middleware like HumanInTheLoopMiddleware for approval workflows, custom error handling, and human-in-