Defensive followup to the relevance fix. Deezer's advanced search
syntax (`artist:"X"`) is documented as substring match, but in
practice it's brittle on artist name variants ("Foreigner [US]",
"The Foreigner") and on tracks indexed under non-canonical title
spellings. When the advanced query returns nothing, we'd previously
land at "No matches" — a regression vs. pre-fix behaviour where
free-text would have returned a less-relevant but non-empty set.
Fix: when the advanced query returns 0 results AND the caller used
field-scoped kwargs, fall back to a free-text join of the same
kwargs and re-query. Caller-side rerank still tightens whatever the
fallback returns, so the worst-case post-fix behaviour is the
pre-fix behaviour — never strictly worse.
Pulled the cache + parse + store dance into a private helper
(`_search_tracks_with_query`) so the orchestration can call it
twice (advanced → fallback) without code duplication. Single API
call when the advanced query has results — no wasted requests.
Diagnostic logger.debug fires when the fallback triggers so we can
see in production whether it's happening (and to which queries).
# Tests added (4)
- `test_falls_back_to_free_text_when_advanced_empty` — advanced
query returns 0, free-text returns hits; client returns the
free-text hits + both API calls fire.
- `test_no_fallback_when_advanced_query_has_results` — single hit
on advanced query → no second API call.
- `test_no_fallback_when_legacy_free_text_call` — legacy callers
already exhausted the only path; empty result is final.
- `test_no_fallback_when_query_unchanged` — empty kwargs path
doesn't trigger the fallback branch (used_advanced=False).
# Existing tests updated
The 4 prior `TestSearchTracksQueryWiring` + `TestSearchTracksCacheKey`
tests were stubbing `_api_get` to return empty `{'data': []}` and
asserting `assert_called_once`. With the new fallback, those stubs
trigger a second API call and the assertions break — even though
the FIRST call construction is what the tests cared about. Updated
the stubs to return one fake hit so the fallback doesn't fire, and
switched to `call_args_list[0]` for first-call inspection.
# Verification
- 18/18 deezer query tests pass (14 prior + 4 new)
- 2445 full suite passes (+4 from prior commit)
- Ruff clean
59992d42a8