fix(engine): 保留并正交化平面 y_dir 方向

backend/engine/cdsl_engine/sketch_solver.py

@@ -44,14 +44,33 @@ def _to_3d(workplane: _Ctx, u: float, v: float) -> list[float]:
     origin = workplane.get("origin_mm") or [0, 0, 0]
     x_dir = workplane.get("x_dir") or [1, 0, 0]
     normal = workplane.get("normal") or [0, 0, 1]
-    y_dir = [
-        normal[1] * x_dir[2] - normal[2] * x_dir[1],
-        normal[2] * x_dir[0] - normal[0] * x_dir[2],
-        normal[0] * x_dir[1] - normal[1] * x_dir[0],
-    ]
+    y_raw = workplane.get("y_dir")
+    y_dir = _default_y_dir(x_dir, normal)
+    if y_raw:
+        magnitude = math.sqrt(sum(component * component for component in y_raw))
+        if magnitude > 1e-12:
+            y_unit = [component / magnitude for component in y_raw]
+            # 与 PlaneSpec.from_mapping 同策略：只有与 x_dir / normal 正交的
+            # y_dir 才尊重（SolidWorks 导出的 y_dir==x_dir 占位数据与 X 平行，
+            # 直接使用会让轮廓塌缩成一条线，必须回退到 normal×x_dir）。
+            if abs(_dot(y_unit, x_dir)) <= 1e-6 and abs(_dot(y_unit, normal)) <= 1e-6:
+                y_dir = y_unit
     return [origin[0] + u * x_dir[0] + v * y_dir[0], origin[1] + u * x_dir[1] + v * y_dir[1], origin[2] + u * x_dir[2] + v * y_dir[2]]
 
 
+def _dot(left: Iterable[float], right: Iterable[float]) -> float:
+    return sum(a * b for a, b in zip(left, right))
+
+
+def _default_y_dir(x_dir: Iterable[float], normal: Iterable[float]) -> list[float]:
+    x, n = list(x_dir), list(normal)
+    return [
+        n[1] * x[2] - n[2] * x[1],
+        n[2] * x[0] - n[0] * x[2],
+        n[0] * x[1] - n[1] * x[0],
+    ]
+
+
 def _transform_contours(contours: list[_Ctx], workplane: _Ctx) -> list[_Ctx]:
     transformed: list[_Ctx] = []
     normal = workplane.get("normal") or [0, 0, 1]