feat: config-authoritative conf gates + cross-model IoU sack suppression

tests/test_config_loader.py

@@ -84,6 +84,7 @@ def test_counting_knobs_match_production_defaults(repo_config_path):
     assert c.exit_overlap_threshold == 0.05
     assert c.camera_noise_deadband == 50
     assert c.duplicate_circle_radius == 30
+    assert c.cross_class_iou == 0.4
     assert c.min_valid_area == 15000
     assert c.max_reid_transit_distance == 400
     assert c.circle_stay_timeout_sec == 10.0

tests/test_counting.py

@@ -96,3 +96,19 @@ def test_multiclass_geometry_sync_and_reset():
     assert c.loading_count == 1
     c.reset()
     assert (c.loading_count, c.box_loading_count, c.box_net_count) == (0, 0, 0)
+
+def test_drop_sacks_overlapping_boxes():
+    from src.counting import drop_sacks_overlapping_boxes
+    box = _det(9, y1=100, cx=500.0, class_name="box")
+    # identical footprint -> IoU 1.0 >= 0.4 -> sack dropped
+    assert drop_sacks_overlapping_boxes([_det(1, y1=100, cx=500.0)], [box]) == []
+    # partial overlap (cx 515) -> IoU ~0.45 -> dropped
+    assert drop_sacks_overlapping_boxes([_det(2, y1=100, cx=515.0)], [box]) == []
+    # no overlap -> kept
+    kept = drop_sacks_overlapping_boxes([_det(3, y1=100, cx=700.0)], [box])
+    assert len(kept) == 1 and kept[0].track_id == 3
+    # no boxes / disabled -> kept
+    assert len(drop_sacks_overlapping_boxes([_det(4, y1=100)], [], 0.4)) == 1
+    assert len(drop_sacks_overlapping_boxes([_det(5, y1=100)], [box], 0.0)) == 1
+    # box dets in sack list never dropped
+    assert len(drop_sacks_overlapping_boxes([_det(6, y1=100, class_name="box")], [box])) == 1