The unit specs for these helpers lived in the readers #5856 patched, both
deleted here, leaving the album-root promotion and the artist-folder climb
covered only end-to-end. A layout can show which image won but not why, so
these pin the parts behind it: that the parent is fetched only when it could
qualify as an album root, that a failed fetch propagates or degrades, and
that commonDir keeps a shared name fragment from reading as a shared folder.
Each spec was checked against a mutant: removing the library-root guard, the
other-album audio check, the single-folder short circuit, the single-root
climb, or commonDir's separator all turn one red.
Master's remaining specs were dropped as redundant — they cover sources this
branch already exercises under different names.
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