- search: paste a playlist link → it resolves to a 'YouTube playlist' chip
(cover, owner, count) with Add-to-watchlist; clicking the chip opens it.
(isPlaylistRef + playlistCard + followPlaylist/unfollowPlaylist helpers.)
- routing: /video-detail/youtube/playlist/<PL…> deep-links like a channel
(string id); the open-detail event handles kind='playlist'.
- detail view: a FLAT list in the curator's order (no year-seasons, no season
nav / view toggle, no catalog streaming — it's a partial set). Billboard shows
'Playlist · N videos · owner'. Reuses the show-detail shell + the new
duration/views cards.
- watchlist: followed playlists sit beside channels in the Channels tab (rounded
square + a list badge), open on click, ✕ to unfollow.
Live-validated (Lex Fridman playlist resolves + renders in order). The 2 shell
test 'failures' are the pre-existing window.-assertion (no new globals added).
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