diff --git a/backend/engine/cdsl_engine/build123d_adapter.py b/backend/engine/cdsl_engine/build123d_adapter.py
index 511f117d..109d5c1c 100644
--- a/backend/engine/cdsl_engine/build123d_adapter.py
+++ b/backend/engine/cdsl_engine/build123d_adapter.py
@@ -9,12 +9,10 @@ from build123d import Axis, Edge, Face, Plane, Solid, Vector, Wire, export_step
 
 from .runtime_types import AxisSpec, HoleSpec, PlaneSpec, TopologyRecord, Vector3, canonical_plane_signature
 
-
 def _vector(value: list[float] | tuple[float, float, float]) -> Vector:
     # 将三元坐标（list 或 tuple）转换为 build123d 的 Vector 对象。
     return Vector(float(value[0]), float(value[1]), float(value[2]))
 
-
 def _arc_midpoint(edge: dict[str, Any], start: Vector, end: Vector, center: Vector) -> Vector:
     # 计算圆弧中点（配合 Edge.make_three_point_arc 三点画弧），支持显式法向与顺时针/逆时针方向。
     # 1. 半径：优先取 edge.radius_mm，缺省时由圆心到起点的距离推算。