Rich link previews

curl -sS -X POST "https://api.relayapp.im/v1/messages" \
  -H "Authorization: Bearer $RELAY_AGENT_TOKEN" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: link-evt_01JZE9M2XW" \
  -d '{
    "conversation_id": "cnv_01JZC7K4RQ",
    "parts": [{
      "type": "link_preview",
      "url": "https://example.com/article"
    }]
  }'

{
  "parts": [
    { "type": "text", "text": "This is the source I used:" },
    { "type": "link_preview", "url": "https://example.com/article" }
  ]
}