fix(demo): correct window start metadata and test unpacking

Use buffered frame indices for emitted window bounds to stay accurate across detection gaps, and align select_person tests with the 4-field return contract introduced for frame-space bbox support.

tests/demo/test_window.py

@@ -234,7 +234,7 @@ class TestSelectPerson:
         result = select_person(results)
 
         assert result is not None
-        mask, bbox, tid = result
+        mask, bbox, _, tid = result
         assert mask.shape == (100, 100)
         assert bbox == (10, 10, 50, 90)
         assert tid == 42
@@ -257,7 +257,7 @@ class TestSelectPerson:
         result = select_person(results)
 
         assert result is not None
-        mask, bbox, tid = result
+        mask, bbox, _, tid = result
         assert bbox == (0, 0, 30, 30)  # Largest box
         assert tid == 2  # Corresponding track ID
 
@@ -327,7 +327,7 @@ class TestSelectPerson:
         result = select_person(results)
 
         assert result is not None
-        _, bbox, tid = result
+        _, bbox, _, tid = result
         assert bbox == (10, 10, 50, 90)
         assert tid == 1
 
@@ -341,11 +341,10 @@ class TestSelectPerson:
         result = select_person(results)
 
         assert result is not None
-        mask, _, _ = result
+        mask, _, _, _ = result
         # Should be 2D (extracted from expanded 3D)
         assert mask.shape == (100, 100)
 
-
     def test_select_person_tensor_cpu_inputs(self) -> None:
         """Tensor-backed inputs (CPU) should work correctly."""
         boxes = torch.tensor([[10.0, 10.0, 50.0, 90.0]], dtype=torch.float32)
@@ -356,7 +355,7 @@ class TestSelectPerson:
         result = select_person(results)
 
         assert result is not None
-        mask, bbox, tid = result
+        mask, bbox, _, tid = result
         assert mask.shape == (100, 100)
         assert bbox == (10, 10, 50, 90)
         assert tid == 42
@@ -372,7 +371,7 @@ class TestSelectPerson:
         result = select_person(results)
 
         assert result is not None
-        mask, bbox, tid = result
+        mask, bbox, _, tid = result
         assert mask.shape == (100, 100)
         assert bbox == (10, 10, 50, 90)
         assert tid == 42
@@ -394,6 +393,6 @@ class TestSelectPerson:
         result = select_person(results)
 
         assert result is not None
-        _, bbox, tid = result
+        _, bbox, _, tid = result
         assert bbox == (0, 0, 30, 30)  # Largest box
         assert tid == 2  # Corresponding track ID