curl -X POST "https://api.cartesia.ai/agents/documents" \
  -H "X-API-Key: your-api-key" \
  -H "Cartesia-Version: 2025-04-16" \
  -H "Content-Type: application/json" \
  -d '{
    "folder_id": "folder_abc",
    "name": "Return Policy",
    "content": "Customers may return any unopened item within 30 days...",
    "metadata": {"category": "policy", "audience": "customer"}
  }'

{
  "id": "<string>",
  "name": "<string>",
  "content": "<string>",
  "created_at": "2023-11-07T05:31:56Z",
  "metadata": {}
}