Step 5. A URL goes through the same pipeline as an upload — it just gains a
download step and a source_url.
- The host allowlist is checked on the parsed hostname before yt-dlp is
invoked, so lookalikes and userinfo tricks are refused too
- yt-dlp -J reads metadata synchronously with a 15s timeout; a timeout leaves
the fields blank rather than failing the submission
- Over-long tracks are refused from that metadata, before a byte is downloaded
- Failed URL submissions offer Yritä uudelleen with the typed text intact;
uploads cannot retry, so they offer re-upload
Prefill takes track then title, and artist then creator then uploader, and
leaves a field blank rather than inventing one. testdata/ytdlp-noose.json is a
real dump of an ordinary upload, which has none of the music fields.
Also fixes a URL-only submit being blocked by the file input's required
attribute — HTML cannot express "one of these two", so the server says it.
The image now takes yt-dlp from Alpine 3.24 instead of pip, which drops
python3 and pip entirely; see decision 19.
