YouTube's flat playlist extraction returns ONLY the title (verified: no artist/channel/uploader
field at all), so a track starts as 'Unknown Artist' and only gains a name if per-video recovery
succeeds. When recovery comes up empty (no cookies / age-gated / bot-checked) but the track still
matched confidently, the worker threw the match's artist away and left the column 'Unknown Artist'
— the #909 symptom.
Now the displayed yt_artist falls back to the matched artist when it's still Unknown. Display-only:
the match itself, track['artists'], cache, and download flow are untouched, so a real recovered
name always wins and an unmatched/error row honestly stays Unknown. Extracted resolve_display_artist
as a pure, tested seam; applied in the cache-hit and fresh-match result paths (the error path has
no match to draw from).
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