Builds a peer-to-peer team of agents that hand control to one another.

Every agent can transfer the conversation to any other agent. The currently active agent is tracked in the :active_agent state key and persisted across invocations via the graph's checkpointer, so a follow-up message resumes with whichever agent last held the conversation.

graph =
  LangEx.Prebuilt.Swarm.create(
    agents: [
      [name: :router, model: "gpt-4o", system_prompt: "Route the user."],
      [name: :refunds, model: "gpt-4o", system_prompt: "Handle refunds."]
    ],
    default_active_agent: :router,
    checkpointer: LangEx.Checkpointer.Memory
  )

{:ok, state} =
  LangEx.invoke(graph, %{messages: [LangEx.Message.human("I want a refund")]},
    config: [thread_id: "t-1"]
  )

Each agent is given a handoff tool (transfer_to_<peer>) for every other agent automatically; no manual wiring is required.