feat(enrichment): loose MusicBrainz search fallback (find aliased artists)

The MB text search used a strict field-phrase query
(`recording:"<title>" AND artist:"<artist>"`). A field phrase only matches
MusicBrainz's *primary* artist/title — it never searches ALIASES — so a
recording stored under a non-Latin primary name (大橋純子) whose romanized
form ("Junko Ohashi") is only an alias returns ZERO results, even though MB
has it. Whole swaths of a community library (e.g. romanized J-pop / city-pop
charts) were unsearchable.

- `build_recording_query(..., loose=True)` drops the field scoping + phrases
  for plain AND-ed term groups (`(telephone number) AND (junko ohashi)`),
  which searches the whole document incl. aliases.
- `_mb_search_recordings` runs the strict query first (unchanged, high
  precision) and only on an EMPTY result retries once with the loose query —
  so mainstream matches are untouched and the extra throttled request is spent
  only on a miss. Results are re-scored by rank_candidates, so recall goes up
  without lowering match quality (auto-accept still needs the per-field floors).

Verified live: "Junko Ohashi / Telephone Number" and "Anri / Windy Summer"
(both 0 under the strict query) now surface the real records; "AC/DC /
Highway to Hell" still hits strict at score 1.0 with no loose retry.

Follow-up (separate): alias-aware SCORING so these can auto-confirm, not just
appear as manual candidates.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/mb_match.py

@@ -198,12 +198,29 @@ def _lucene_escape_phrase(s: str) -> str:
     return s.replace("\\", "\\\\").replace('"', '\\"')
 
 
-def build_recording_query(artist, title) -> str:
+def build_recording_query(artist, title, *, loose: bool = False) -> str:
     """Lucene query for /ws/2/recording. Built from the DENOISED fields —
     the noise we strip (author credits, "(Live)", "(v2)") would otherwise
-    poison the search server's own scoring."""
+    poison the search server's own scoring.
+
+    ``loose=True`` drops the field-scoped quoted PHRASES for plain AND-ed
+    term groups (``(telephone number) AND (junko ohashi)``). The point:
+    a field phrase like ``artist:"Junko Ohashi"`` only matches MusicBrainz's
+    *primary* artist name — it never searches ALIASES — so a recording stored
+    under a non-Latin primary (大橋純子) whose romanized name is only an alias
+    is invisible to the strict query. A loose term query searches the whole
+    document, aliases included, and surfaces it. Lower precision by design: it
+    is a FALLBACK for when the strict query returns nothing, and its results
+    are re-scored by ``rank_candidates`` (and, for auto-match, gated by the
+    per-field floors), so noise never auto-applies."""
     t = denoise(title)
     a = denoise(artist)
+    if loose:
+        # denoise() already reduced each field to lowercase [a-z0-9 and] tokens
+        # (punctuation → spaces, diacritics stripped, & → "and"), so no
+        # Lucene-special character survives to need escaping. Group each field's
+        # terms and require both groups.
+        return " AND ".join("(%s)" % g for g in (t, a) if g)
     parts = []
     if t:
         parts.append('recording:"%s"' % _lucene_escape_phrase(t))

server.py

@@ -6236,12 +6236,27 @@ def _mb_http_get(path: str, params: dict) -> dict | None:
 
 
 def _mb_search_recordings(artist, title, limit: int = 8) -> list[dict]:
-    """Text search (tier 2–4): denoised Lucene query over /recording."""
+    """Text search (tier 2–4): denoised Lucene query over /recording.
+
+    Runs the strict field-phrase query first (high precision, unchanged); if it
+    finds nothing, retries ONCE with a loose term query. The strict phrase only
+    matches MusicBrainz's *primary* artist/title, so a recording stored under a
+    non-Latin primary name (大橋純子) whose romanized form ("Junko Ohashi") is
+    only an alias is invisible to it — the loose query searches aliases and
+    rescues it. The retry spends a second throttled request only on a miss;
+    results are re-scored by rank_candidates, so the looser recall doesn't lower
+    match quality (auto-accept still needs the per-field floors)."""
     query = mb_match.build_recording_query(artist, title)
-    if not query:
+    cands: list[dict] = []
-        return []
+    if query:
         body = _mb_http_get("recording", {"query": query, "limit": limit})
-    return mb_match.parse_search_response(body or {})
+        cands = mb_match.parse_search_response(body or {})
+    if not cands:
+        loose = mb_match.build_recording_query(artist, title, loose=True)
+        if loose and loose != query:
+            body = _mb_http_get("recording", {"query": loose, "limit": limit})
+            cands = mb_match.parse_search_response(body or {})
+    return cands
 
 
 def _mb_lookup_recording(mbid: str) -> dict | None:

tests/test_mb_enrichment.py

@@ -97,6 +97,43 @@ def mb_doc(rid="rec-1", title="Thunderstruck", artist="AC/DC", artist_id="art-1"
     }
 
 
+# ── strict-then-loose search fallback ────────────────────────────────────────
+
+def test_search_falls_back_to_loose_when_strict_is_empty(server, monkeypatch):
+    """The strict field-phrase query misses a non-Latin-primary artist; the
+    loose retry (no field scoping) searches aliases and finds it."""
+    calls = []
+
+    def _routed(path, params):
+        q = params.get("query", "")
+        calls.append(q)
+        if q.startswith("recording:"):        # strict phrase → nothing
+            return {"recordings": []}
+        return {"recordings": [mb_doc(rid="rec-x", title="Telephone Number")]}
+
+    monkeypatch.setattr(server, "_mb_http_get", _routed)
+    cands = server._mb_search_recordings("Junko Ohashi", "Telephone Number")
+    assert len(cands) == 1
+    assert len(calls) == 2                     # strict first, then the loose retry
+    assert calls[0].startswith("recording:")   # strict is the field-phrase form
+    assert "artist:" not in calls[1] and '"' not in calls[1]   # loose retry
+
+
+def test_search_does_not_retry_when_strict_hits(server, monkeypatch):
+    """A strict hit must not spend a second (throttled) request on the loose
+    query."""
+    calls = []
+
+    def _routed(path, params):
+        calls.append(params.get("query", ""))
+        return {"recordings": [mb_doc()]}
+
+    monkeypatch.setattr(server, "_mb_http_get", _routed)
+    cands = server._mb_search_recordings("AC/DC", "Thunderstruck")
+    assert len(cands) == 1
+    assert len(calls) == 1
+
+
 # ── offline safety (the pytest-never-hits-network contract) ──────────────────
 
 def test_offline_default_skips_matching(server, monkeypatch):

tests/test_mb_match.py

@@ -160,6 +160,21 @@ def test_build_recording_query_escapes_and_handles_missing_artist():
     assert "artist:" not in q
 
 
+def test_build_recording_query_loose_drops_field_phrases():
+    # The strict form (unchanged) locks to the *primary* artist/title phrase.
+    assert m.build_recording_query("Junko Ohashi", "Telephone Number") == \
+        'recording:"telephone number" AND artist:"junko ohashi"'
+    # The loose form has no field scoping and no phrases, so MusicBrainz also
+    # searches artist ALIASES — rescues non-Latin-primary artists (大橋純子).
+    loose = m.build_recording_query("Junko Ohashi", "Telephone Number", loose=True)
+    assert loose == "(telephone number) AND (junko ohashi)"
+    assert "artist:" not in loose and '"' not in loose
+
+
+def test_build_recording_query_loose_missing_artist():
+    assert m.build_recording_query("", "Fantasy", loose=True) == "(fantasy)"
+
+
 # ── MusicBrainz response parsing ──────────────────────────────────────────────
 
 MB_DOC = {