feat(perception): qualify conservative static occupancy

src/k1link/perception/geometry.py

@@ -344,6 +344,28 @@ class RecordedGeometryStore:
         points.setflags(write=False)
         return points
 
+    def point_step_candidates_for_frame(self, frame_index: int) -> UInt8Array | None:
+        """Expose the sealed low-step diagnostic in the source point index space.
+
+        The array is evidence only: a non-zero value may add conservative
+        occupied/unknown support, but it never clears a cell or claims free
+        space.  Unavailable and surface-invalid frames remain unavailable.
+        """
+
+        frame = self.frame_for_index(frame_index)
+        if frame is None or not frame.surface_valid:
+            return None
+        offsets = self._source["cloud_offsets"]
+        start, end = int(offsets[frame_index]), int(offsets[frame_index + 1])
+        values = np.asarray(
+            self._surface["point_step_candidate"][start:end],
+            dtype=np.uint8,
+        )
+        if values.shape != (frame.source_point_count,):
+            raise GeometryProviderError("local-surface step evidence changed")
+        values.setflags(write=False)
+        return values
+
     @property
     def maximum_current_point_count(self) -> int:
         """Return the immutable source-pack upper bound for one recorded increment."""