Multi-disc albums keep their cover in the album-root folder, which the artwork
reader reaches via albumRootParent but which is not in album.folder_ids (only the
disc folders hold media files). A root cover swap therefore advanced the served
cache key without moving the selected artwork version, recreating the stale-hash
deadlock for hash-keyed clients. The version subquery now also considers the
folders' parents. This slightly over-covers (an artist-folder image change can
advance a single-folder album's version), which errs on the side of one spurious
refetch instead of permanent staleness. Plan verified on a 96K-track production
copy: still PK point lookups, outer scan unchanged.
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