Add search and filters inside Watch Later and playlists

The submitted context

Add playlist-scoped search plus filters for channel, watched status, duration, and date added, especially in Watch Later. Large saved lists become impractical to retrieve from by scrolling; a current community request describes trying to find one video among thousands of saved items. YouTube's Watch Later help covers adding and removing videos but no in-list search. The desired outcome is fast retrieval on every device without exporting account data or granting a third-party extension access. Evidence reviewed 2026-08-09: https://www.reddit.com/r/youtube/comments/1ravutj/how_to_search_inside_watch_later_playlist/ https://support.google.com/youtube/answer/56101?hl=en