feat(perception): confirm persistent sparse low steps

tests/test_m48_low_step_occupancy.py

@@ -144,6 +144,28 @@ def test_wide_operator_region_cannot_bridge_two_spatial_components() -> None:
     assert snapshot.failed_frames == 0
 
 
+def test_sparse_component_requires_bounded_causal_persistence() -> None:
+    points = np.asarray(
+        ((0.00, 0.0, 5.00), (0.04, 0.0, 5.00)),
+        dtype=np.float64,
+    )
+    store = _Store(_frame(points), np.ones(2, dtype=np.uint8))
+    provider = M48AdditiveLowStepGeometryProvider(  # type: ignore[arg-type]
+        store=store,
+        profile=load_m48_low_step_occupancy_profile(PROFILE_PATH),
+    )
+
+    first = provider.associate(_packet(0), ())
+    second = provider.associate(_packet(1), ())
+    third = provider.associate(_packet(2), ())
+
+    assert first == ()
+    assert second == ()
+    assert len(third) == 1
+    assert third[0].source_point_ids == (0, 1)
+    assert "additive-low-step-current-component" in third[0].reason_codes
+
+
 def test_frame_1856_preserves_baseline_posts_and_splits_low_hemisphere_support() -> None:
     store = RecordedGeometryStore.from_repository(REPOSITORY_ROOT)
     provider = M48AdditiveLowStepGeometryProvider(