Persist authoritative per-video positions in UserDefaults. Save periodic checkpoints, pause, close, replacement, and quit; restore a validated position before autoplay. Canonical YouTube webpage URLs survive fresh stream extraction, and local symlinks share file progress.
Clear completed or out-of-duration bookmarks. Leave failed opens and live/non-seekable inputs out of persistence. Pending opens hide errors belonging to the previous source.
Verified separate-process restart, source replacement, failed-open recovery, completion, checkpoints, real YouTube short-link resume, live exclusion, and make all check.
Resolve public YouTube URLs through external yt-dlp and play selected streams in the existing native window.
Independent bounded network readers keep one authored timeline. Successful seeks clear FFmpeg's sticky aborted-read AVIO error; manifest seekability uses native format flags rather than a top-level I/O handle.
Verified real YouTube playback, seeking, frame stepping, compact mode, cancellation, and the complete native regression checks.
hl-valdemar