fix(demo): clear stale classification overlay after tracking loss

tests/demo/test_pipeline.py

@@ -790,12 +790,7 @@ def test_pipeline_visualizer_updates_on_no_detection() -> None:
             assert call["confidence"] is None  # No confidence when no detection
 
 
-def test_pipeline_visualizer_uses_cached_detection_on_no_detection() -> None:
-    """Test that visualizer reuses last valid detection when current frame has no detection.
-
-    This is a regression test for the cache-reuse behavior when person temporarily
-    disappears from frame. The last valid silhouette/mask should be displayed.
-    """
+def test_pipeline_visualizer_clears_bbox_on_no_detection() -> None:
     from opengait.demo.pipeline import ScoliosisPipeline
 
     # Create a minimal pipeline with mocked dependencies
@@ -884,7 +879,6 @@ def test_pipeline_visualizer_uses_cached_detection_on_no_detection() -> None:
         assert mask_raw_calls[0] is not None, "Frame 0 should have valid mask"
         assert mask_raw_calls[1] is not None, "Frame 1 should have valid mask"
 
-        # Frames 2 and 3 should reuse the cached mask from frame 1 (not None)
         assert mask_raw_calls[2] is not None, (
             "Frame 2 (no detection) should display cached mask from last valid detection, "
             "not None/blank"
@@ -902,10 +896,21 @@ def test_pipeline_visualizer_uses_cached_detection_on_no_detection() -> None:
         assert segmentation_inputs[1] is not None
         assert segmentation_inputs[2] is not None
         assert segmentation_inputs[3] is not None
+        bbox_calls = [call["bbox"] for call in mock_viz.update_calls]
+        assert bbox_calls[0] == dummy_bbox_frame
+        assert bbox_calls[1] == dummy_bbox_frame
+        assert bbox_calls[2] is None
+        assert bbox_calls[3] is None
         assert bbox_mask_calls[0] == dummy_bbox_mask
         assert bbox_mask_calls[1] == dummy_bbox_mask
-        assert bbox_mask_calls[2] == dummy_bbox_mask
-        assert bbox_mask_calls[3] == dummy_bbox_mask
+        assert bbox_mask_calls[2] is None
+        assert bbox_mask_calls[3] is None
+        label_calls = [call["label"] for call in mock_viz.update_calls]
+        confidence_calls = [call["confidence"] for call in mock_viz.update_calls]
+        assert label_calls[2] is None
+        assert label_calls[3] is None
+        assert confidence_calls[2] is None
+        assert confidence_calls[3] is None
 
         if mask_raw_calls[1] is not None and mask_raw_calls[2] is not None:
             assert mask_raw_calls[1] is not mask_raw_calls[2], (