AgentFileRelay public temporary file service

POST /upload
  multipart/form-data: file=<file>, ttlSeconds=<optional>
  application/json: {"filename":"name.ext","contentBase64":"...","ttlSeconds":7200}
  application/octet-stream: raw body, filename from ?filename= or X-Filename

GET /f/{file_id}/{filename}
GET /d/{file_id}/{delete_token}

Files are public, unlisted, random-url addressed, and automatically expire.