feat: add candidate ranker with confidence gate

worker/lyra_worker/ranker.py

@@ -0,0 +1,15 @@
+from dataclasses import replace
+
+from lyra_worker.confidence import score_confidence
+from lyra_worker.quality import rank_key
+from lyra_worker.types import Candidate, MBTarget
+
+
+def rank_candidates(
+    target: MBTarget, candidates: list[Candidate], min_confidence: float = 0.7
+) -> list[Candidate]:
+    """Score, gate by confidence, and sort best-first (quality, then confidence)."""
+    scored = [replace(c, confidence=score_confidence(target, c)) for c in candidates]
+    kept = [c for c in scored if c.confidence >= min_confidence]
+    kept.sort(key=lambda c: (rank_key(c), c.confidence), reverse=True)
+    return kept

worker/tests/test_ranker.py

@@ -0,0 +1,42 @@
+from lyra_worker.ranker import rank_candidates
+from lyra_worker.types import Candidate, MBTarget, Quality
+
+HIRES = Quality(fmt="FLAC", lossless=True, bit_depth=24, sample_rate=96000)
+CD = Quality(fmt="FLAC", lossless=True, bit_depth=16, sample_rate=44100)
+MP3 = Quality(fmt="MP3", lossless=False, bitrate_kbps=320)
+TARGET = MBTarget(artist="Radiohead", album="In Rainbows", track_count=10)
+
+
+def _cand(source, quality, artist="Radiohead", album="In Rainbows", tracks=10):
+    return Candidate(source=source, source_ref=f"{source}:{quality.fmt}",
+                     matched_artist=artist, matched_album=album,
+                     quality=quality, track_count=tracks)
+
+
+def test_returns_empty_for_no_candidates():
+    assert rank_candidates(TARGET, []) == []
+
+
+def test_best_quality_wins_among_correct_matches():
+    ranked = rank_candidates(TARGET, [
+        _cand("youtube", MP3),
+        _cand("qobuz", HIRES),
+        _cand("soulseek", CD),
+    ])
+    assert [c.source for c in ranked] == ["qobuz", "soulseek", "youtube"]
+    assert all(c.confidence > 0.9 for c in ranked)
+
+
+def test_confidence_gate_drops_wrong_album_even_if_higher_quality():
+    ranked = rank_candidates(TARGET, [
+        _cand("qobuz", HIRES, album="OK Computer", tracks=12),  # wrong release, hi-res
+        _cand("soulseek", CD),                                   # correct, lossless
+    ])
+    assert [c.source for c in ranked] == ["soulseek"]
+
+
+def test_all_below_threshold_returns_empty():
+    ranked = rank_candidates(TARGET, [
+        _cand("qobuz", HIRES, artist="Nirvana", album="Nevermind"),
+    ])
+    assert ranked == []