The FIXME pointed at #2632 (dotted keys in KQL property restrictions),
which is now merged. Use audio.artist — the originally intended target
field for this regression — so the test matches its name: a nested
string field that is not on the lowercase allowlist.
The bleve compiler lowercased every query value (except Hidden)
before handing it to the engine. This matched the index tokens
for fields whose analyzer folds case — Name, Tags, Favorites,
Content — but silently broke matching for every other field,
whose default keyword analyzer preserves case. A query like
Title:"Some Title" parsed fine, lowercased to "some title", and
missed the indexed token "Some Title".
Replace the blanket lowercasing with an allowlist of the four
fields whose index mapping actually uses a lowercasing analyzer.
Every other field now passes through unchanged, which keeps
values like "deadmau5" or "Motörhead" intact instead of
normalising them to a case the tag writer didn't choose.
