curl --request POST \
  --url https://your-instance.example.com/api/email/messages/attachments/rehydrate \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "messageId": "665f1a0c0e0a4b001a2c9f60"
}
'

{
  "message": {
    "_id": "665f1a0c0e0a4b001a2c9f60",
    "conversationId": "665f1a0c0e0a4b001a2c9f70",
    "channelType": "email",
    "body": "Attached the signed lease for review.",
    "attachments": [
      {
        "url": "https://r2.tetherai.ca/org-64a1b/email/lease.pdf?signature=...",
        "contentType": "application/pdf",
        "size": 184320,
        "filename": "lease.pdf"
      }
    ]
  },
  "rehydrated": 1
}