動的なターン

$agent = AgentSdk::createAgent(new AgentDefinition(
    id: "support-agent",
    model: fn ($turn) => $turn->run->stepCount > 3
        ? "openai/gpt-5.4"
        : "openai/gpt-5.4-nano",
    instructions: fn ($turn) => "Resolve the request using the current context."
));