为某个智能体创建咏唱引擎云会话

POST /v1/agents/sessions

curl -X POST https://agent.example.com/v1/agents/sessions \
  -H "Authorization: Bearer $ARIA_AGENT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"agent_id": "ag_0198a...", "metadata": {"user_id": "u_42"}}'

{
  "id": "sess_0198c...",
  "object": "agent.session",
  "agent_id": "ag_0198a...",
  "status": "active",
  "metadata": {"user_id": "u_42"},
  "created_at": 1735000000
}