A bare `pip install yt-dlp` lacks mutagen and the YouTube challenge solver

Fact

Every dependency of the yt-dlp package sits behind an extra; the bare install pulls in nothing. yt-dlp[default] adds, among others, mutagen and yt-dlp-ejs, and two features fail without them:

• Cover art in ogg, opus and flac is written only through mutagen. Without it, the thumbnail step raises module mutagen was not found and the whole video counts as failed. mp3 and m4a embed through ffmpeg, so a test on mp3 passes.
• YouTube's JavaScript challenge needs a runtime (Deno by default) and the solver script from yt-dlp-ejs. Installing Deno alone swaps the "No supported JavaScript runtime" warning for "challenge solver script ... were skipped" and "n challenge solving failed: Some formats may be missing".

Why it matters

Both look like environment trouble rather than a packaging gap, and the usual fix (install mutagen, install Deno) each solves half of the problem.

How to apply

• Depend on yt-dlp[default], never bare yt-dlp, in a project that embeds it. yt-dlp[default,deno] also brings Deno through pip.
• Without the extra, --remote-components ejs:github downloads the solver at run time.
• Confirm with a metadata-only run (yt-dlp -s URL): no [jsc] or n challenge lines means the challenge was solved.