Backend

ytdlp.js: URL validation, argument building and progress parsing, kept out of server.js so the tests can import it without starting the server
playlist download: optional "playlist" flag, --yes-playlist capped by MAX_PLAYLIST_ITEMS, per-item progress on the job, MAX_CONCURRENT_JOBS guard
ID3: promo suffixes stripped, artist/title derived from the video title, playlist name as album, optional EBU R128 normalization (off by default)
AUDIO_FORMAT and AUDIO_QUALITY are env vars instead of hardcoded
/api/health reports version and features, so the extension can hide UI an older backend cannot serve
the API no longer creates the target folder: yt-dlp does. A root API container and a non-root yt-dlp container can no longer split its ownership
test-server.js: 11 assertions covering validators and argument building
Extension

favorite folders and last used folder, one click away in the popup
playlist checkbox, shown only for a playlist URL on a capable backend
background service worker: notifies when a download ends with the popup closed. "notifications" is an optional permission, requested on first use
reopening the popup during a download restores log and progress: nothing is kept locally, the job log is replayed from the API
the API base URL is normalized on save. Without a scheme every request resolved against chrome-extension://, surfacing as "network error"
Docs: new env vars and playlist usage in README; compose runs yt-dlp as 1000:1000 with a writable HOME so its cache works.