Moving agent calls into the worker bypassed two behaviors of the aggregate provider:
Agents.GetArtistImages' guard for Unknown/Various Artists (a direct retriever call
could assign an unrelated image to a synthetic artist), and auxAlbum/auxArtist.Name's
DevPreserveUnicodeInExternalCalls normalization (records with typographic quotes/dashes
missed exact-name searches). Re-apply both before enumerating retrievers.