fix: stop re-gating gallery scores in the live path

`score_crop` returns only scores the gallery already accepted: the raw 0.55
line, or the fine-tuned head's own 0.40. The live path then ranked that
aggregate with `decide_identity(scale="cosine")`, whose defaults rewrite to
COSINE_ACCEPT 0.60 / COSINE_AMBIGUOUS 0.50 - a second, higher line. Every head
match between 0.40 and 0.60 was therefore refused or downgraded to ambiguous,
which is the live regression: the head's own training views score 0.57-0.77.

`engine.inspect` and `_classify_with_gallery` already avoid this by ranking
through `decision_for_match`, which applies only the published margin. The live
path now does the same: on the cosine scale it passes explicit zero accept
lines, so the margin gate is the only extra gate.

Regression tests: a 0.45 head-scale match is labelled (fails on the previous
code), and a 0.45/0.44 pair inside the margin stays unnamed.

Verified: `python -m unittest discover -s code -p 'test_*.py'` - 257 tests, OK,
2 skipped.

recognization/code/live.py

@@ -1146,9 +1146,17 @@ class LiveSession:
             from identity import aggregate_votes, decide_identity
 
             mean_scores = aggregate_votes(track.observations)
-            decision = decide_identity(
-                mean_scores, method=method, scale=getattr(self.engine, "identity_scale", "inlier")
-            )
+            if getattr(self.engine, "identity_scale", "inlier") == "cosine":
+                # score_crop only returns a score the gallery already accepted, so
+                # the aggregate must not be re-gated at COSINE_ACCEPT: that line is
+                # above the head's own 0.40 and refused matches the gallery had
+                # accepted. Only the margin gate is left to apply.
+                decision = decide_identity(
+                    mean_scores, method=method, scale="cosine",
+                    min_score=0.0, min_confidence=0.0,
+                )
+            else:
+                decision = decide_identity(mean_scores, method=method)
             track.candidates = [
                 {"sku_id": row.get("sku_id"), "score": row.get("score")}
                 for row in (decision.get("ranked_candidates") or [])[:3]

recognization/code/test_live.py

@@ -63,6 +63,18 @@ class FakeMatcher:
         return self.score_crop(crop)
 
 
+class CosineEngine(RecognitionEngine):
+    """A gallery-scale engine: score_crop only returns scores the gallery accepted."""
+
+    @property
+    def identity_scale(self):
+        return "cosine"
+
+    def score_crop(self, crop, method=None):
+        scores, _ = self.matcher.score_crop(crop, method or "hybrid")
+        return scores
+
+
 class FakeInventory:
     """Stateful stand-in for InventoryManager, so stock assertions are real."""
 
@@ -94,11 +106,11 @@ class FakeInventory:
         return True
 
 
-def make_session(matcher=None, settings=None):
+def make_session(matcher=None, settings=None, engine_cls=RecognitionEngine):
     detector = FakeDetector()
     matcher = matcher or FakeMatcher()
-    engine = RecognitionEngine(detector, matcher, FakeInventory(),
-                               settings=__import__("engine").EngineSettings(classify_workers=2))
+    engine = engine_cls(detector, matcher, FakeInventory(),
+                        settings=__import__("engine").EngineSettings(classify_workers=2))
     session = LiveSession("test", engine, settings=settings or LiveSettings(method="hybrid"))
     session.refresh_catalog()
     return session, engine, detector, matcher
@@ -203,6 +215,37 @@ class LabelLifecycleTests(unittest.TestCase):
         engine.shutdown()
 
 
+class CosineScaleTests(unittest.TestCase):
+    """A gallery-scale score is gated by the gallery, not re-gated by the live path."""
+
+    def test_a_head_scale_match_is_labelled(self):
+        """0.45 clears the head's own 0.40 line but not COSINE_ACCEPT (0.60).
+
+        score_crop only returns scores the gallery already accepted, so the live
+        aggregate must not re-apply the cosine accept line: that refused every
+        head match the gallery had accepted, which is the live regression.
+        """
+        session, engine, _, _ = make_session(FakeMatcher(score=0.45), engine_cls=CosineEngine)
+        for frame_id in range(1, 5):
+            process(session, frame_id)
+        self.assertTrue(wait_for(lambda: any(
+            track["identity"]["state"] == "recognized" for track in process(session, 5)["tracks"]
+        )), "a gallery-accepted head match must be labelled")
+        engine.shutdown()
+
+    def test_a_close_cosine_pair_stays_ambiguous(self):
+        """The margin gate still applies: two near-equal scores must not name a SKU."""
+        session, engine, _, _ = make_session(FakeMatcher(score=0.45), engine_cls=CosineEngine)
+        engine.matcher.score_crop = lambda crop, method=None: {"sku_a": 0.45, "other": 0.44}
+        for frame_id in range(1, 8):
+            process(session, frame_id)
+        result = process(session, 9)
+        for track in result["tracks"]:
+            self.assertIsNone(track["identity"]["sku_id"],
+                              "a cosine pair inside the margin must not be named")
+        engine.shutdown()
+
+
 class TagPassIntegrationTests(unittest.TestCase):
     """The tag pass must reach the live result without blocking frames."""