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.
hl-valdemar