fix(engine): 接受 hole_wizard 的 thread 装饰并按光滑孔降级执行

backend/engine/cdsl_engine/runtime.py

@@ -501,8 +501,18 @@ def _execute_hole(node: FeaturePlanNode, session: ExecutionSession, *, wizard: b
         session.adapter.body_span(session.body, inward) + 2.0,
     )
     # 6. 从主体上减去工具实体，登记新主体并返回结果。
+    #    thread 是装饰螺纹（无螺距、不进实体几何，SolidWorks/STEP 的螺纹孔
+    #    即光滑孔）：孔按光滑圆柱孔执行，同时记录 info 级诊断便于批量报告
+    #    追溯降级数量（issue #9，capabilities 已不再拒绝 thread）。
+    diagnostics: list[RuntimeDiagnostic] = []
+    if wizard and node.params.get("thread"):
+        diagnostics.append(RuntimeDiagnostic(
+            code="thread_decoration_ignored",
+            message="Thread decoration is not modeled; the hole falls back to a plain cylindrical bore",
+            feature_id=node.feature_id,
+        ))
     session.register_body(node.feature_id, session.adapter.cut(session.body, tool), replay_node=node)
-    return session.result(node)
+    return session.result(node, diagnostics=diagnostics)
 
 
 def _selector_edges(node: FeaturePlanNode, session: ExecutionSession, *, tangent_propagation: bool = False) -> list[Any]: