Flat channel listing can't return descriptions, so selecting a video showed 'No
description'. Now we do a non-flat single-video extract on demand — the way the
TV nebula lazy-loads guest stars:
- core: video_detail(id) / shape_video() — description, views, likes, duration,
tags, channel, webpage_url (full extract, yt-dlp injectable for tests).
- API: GET /youtube/video/<id> — returns it AND backfills the description onto
the wishlist row (set_wishlist_video_overview), so re-opening is instant.
- Wishlist info bar (youtube): on select, lazy-fetch → real description +
eyebrow (date · duration · views) + a 'Watch on YouTube' link; cached on the
episode object. 'Loading details…' while in flight.
Mirrors the episode lazy-load + art-backfill patterns. 73 youtube+api tests
green; brace/CSS balanced; music untouched.
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