langgraph-fundamentals

| Need fine-grained control over agent orchestration | Quick prototyping → LangChain agents | | Building complex workflows with branching/loops | Simple stateless workflows → LangChain direct | | Require human-in-the-loop, persistence | Batteries-included features → Deep Agents |

| Overwrite value | No reducer (default) | Simple fields like counters | | Append to list | Reducer (operator.add / concat) | Message history, logs | | Custom logic | Custom reducer function | Complex merging |

Define state schema with reducers for accumulating lists and summing integers.

在編寫任何 LangGraph 程式碼時呼叫此技能。涵蓋 StateGraph、狀態模式、節點、邊、命令、傳送、呼叫、流和錯誤處理。 來源：langchain-ai/langchain-skills。