A clip fetched its range signed out, so a video behind YouTube's per-video "not a bot" wall could
never be clipped while its download went through with the user's cookie - and the failure copy told
the user to add a cookie the clip would not use. The clip asset is private by construction
(`clip.asset_ref` names its user), so `usable_clip_cookie` attaches the user's YouTube cookie on that
identity, and a failed range fetch now carries the download catalog's diagnosis
(`youtube.bot_wall` / `youtube.cookie_rejected`) instead of a bare category.
POST /api/downloads/clip takes a source (a YouTube id or a Plex rating key), a range of at most
ten minutes and, for Plex, the audio track being heard. The clip becomes a per-user asset in the
library like an editor clip, shareable as soon as it is ready. A YouTube clip fetches only its
range (yt-dlp download_ranges: 3-7 s whatever the video's length); a Plex clip reads the library
file in place. Both then go through one re-encode: frame-exact at the marks, H.264 at most 1080p
with HDR tonemapped to SDR, stereo AAC, no chapter track, .mp4.
Job kinds are a JobKind StrEnum now, and Re-download refuses every kind but a download.
peter