get_media_source_download

Get a same-origin bearer download path for a stored prepared R2 source video, poster, VTT transcript, transcript JSON, keyframe index (keyframes) or one keyframe/contact sheet (keyframe with name from read_video). Default variant video. Requires live editor/read grant again when bytes are fetched. Pins the R2 ETag/version and length; full downloads only, no Range. ETag is a version guard, not a SHA-256 guarantee. GET path under the same Qraft /api/v1 origin with Authorization header; never put tokens in URLs. No provider refresh, preparation, transcription, new frame capture, original source, storage key, private token or arbitrary path. Legacy Stream and older workers refuse.