feat(cadfs): 补齐核心建模能力并建立代表性回归

- 新增 loft、双向切除、through-all/up-to-next 等 CADFS lowering 与 engine 支持
- 支持多种 reference plane、B-spline profile 和 circular pattern replay
- 保留 transform 历史，并烘焙安全的单源平移/旋转变换
- 改进 selector 绑定、拓扑快照和 pattern 变换处理
- 建立 17 个代表样本的转换、重建与比较回归工具链
- 补充 schema、author guidance、运行时和几何回归测试

cadfs_to_cdsl/README.md

@@ -14,3 +14,28 @@ PYTHONPATH=backend:. python -m cadfs_to_cdsl pipeline
 All stages are resumable. Use `--force` after changing converter behavior.
 The original CADFS directory is read-only; generated evidence is written under
 `cadfs_to_cdsl/output/samples/<sample_id>/`.
+
+## Representative regression pool
+
+Generate the checked-in representative manifest after a full corpus conversion:
+
+```bash
+PYTHONPATH=backend:. python -m cadfs_to_cdsl regression-select
+```
+
+The selector deterministically covers every observed FeatureScript modeling
+operation, sketch entity type, lowered CDSL atomic operation, unsupported
+operation, and unsupported engine-capability variant. It records which atomic
+operations have a successful engine baseline and which are diagnostic-only;
+the latter are never reported as passing builds. A normal engine change has a
+small, executable STEP regression command:
+
+```bash
+PYTHONPATH=backend:. python -m cadfs_to_cdsl regression --tier engine --stage rebuild
+```
+
+The command reruns by default; use `--resume` only to inspect cached results.
+Use `--tier conversion --stage convert` to verify feature lowering and
+diagnostics, or `--tier all --stage pipeline` for the complete representative
+conversion/rebuild/compare pass.  Unsupported CADFS features remain diagnostic
+coverage, not expected successful engine builds.