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Mastering Codex and the OpenAI Agents SDK in 5 Days

D4 The OpenAI Agents SDK: Agents, Handoffs, Guardrails, Sessions, Tracing

• When should you split one agent into several connected by handoffs, and when is a single agent with many tools the better design?什么时候该把一个 Agent 拆成多个、用 handoff 交接？什么时候「一个大 Agent 加很多工具」反而更好？

  Common in ChinaCommon overseasIntermediate#agents-sdk#handoffs#architecture

  How to reason about it · think before answering

  1. This tests your splitting criterion, not API fluency; 'split when there are many tools' is the common wrong answer.
  2. First separate handoffs from tools: a tool call fetches an answer and returns; a handoff transfers the whole conversation so the receiving agent owns it, even though it is implemented as a transfer_to_xxx tool.
  3. The criterion is whether instructions conflict: when two task groups need independent, clashing background, constraints and tone, one instruction block forces constant context switching, longer prompts and more errors, so split; many tools sharing one background do not justify a split.
  4. Name the costs: an extra model call for triage, possible misrouting, input guardrails only on the first agent, and history trimming across agents via inputFilter.
  5. Expect the follow-up: what if triage misroutes? Use RECOMMENDED_PROMPT_PREFIX, assert on lastAgent in regression tests, inspect the handoff turn in tracing, and allow experts to hand back.

  分析过程 · 先想清楚再作答

  1. 这题考的是拆分判据，不是会不会用 API。答「工具多了就拆」是最常见的错误，工具数量不是判据。
  2. 先说清 handoff 与工具的区别：调工具是替你去问一句再回来，handoff 是把对话整个交给另一个 Agent，之后由它负责；实现上 handoff 也是一个名为 transfer_to_xxx 的工具，但语义是转移控制权。
  3. 判据是「指令会不会互相打架」：两组任务需要的背景知识、约束、语气彼此独立且冲突时，塞进一份 instructions 会让模型反复切换上下文、提示越长越贵、出错率上升，这时拆；工具虽多但共享同一套背景的，不拆。
  4. 补拆分的代价：多一次模型调用（分诊那一跳）、路由可能错、输入护栏只在第一个 Agent 上跑、跨 Agent 的历史要靠 inputFilter 裁剪。
  5. 可预期的追问：分诊错了怎么办？用 RECOMMENDED_PROMPT_PREFIX 提高交接准确率，用 lastAgent 做回归断言，用 tracing 看交接发生在哪一轮，必要时让专家 Agent 也能交接回分诊台。

  Key points

  • A handoff transfers conversational control; a tool call only fetches a result
  • Split on conflicting instructions, not on tool count
  • Costs: an extra hop, possible misrouting, input guardrails only on the first agent
  • Control routing quality with the recommended prefix, lastAgent assertions and tracing

  答题要点

  • handoff 转移的是对话控制权，工具调用只是取一次结果
  • 拆分判据是指令是否互相打架，不是工具数量
  • 拆的代价：多一跳、可能路由错、输入护栏只在第一个 Agent 生效
  • 用前缀提示、lastAgent 断言与 tracing 控制路由质量