Read-only. Checks whether a public asset exists (an existence probe,
like a HEAD) — confirm an upload landed, or that a URL you hold still
resolves, before referencing it. Verifies your own academy's public
media only.

Provide the asset in one of two ways — send one, not both:

• By URL — pass url with a public asset URL you received from an
  upload or generate result.
• By path — pass bucket and file_path from an upload's
  { bucket, path } reference.

Requires the media.read scope.