The public page's "viewed" beacon for a read-only handout (ITE-1712): the only thing that marks one read. The page sends it once the handout has been on screen a moment or the reader scrolls or taps, which mail scanners and link previewers never do. The token is in the body, not the path, so it stays out of logs and falls under the form-submit limit. Idempotent: a repeat is 204 and changes nothing. Anything the token can't mark (unknown, expired, taken back, unpublished, not a read-only handout) is the same 404.