feat: integrate SimpleCADAPI 2.0.2 CAD workflows

text-to-cad/skills/cad-router/references/backend-contract.md

@@ -23,6 +23,10 @@ Capture these fields when known:
 Record:
 
 - `selected_backend`: `build123d` or `simplecadapi`.
+- `routing_policy.effective_execution_engine`: the actual engine. It is
+  `surfaceir` for an uploaded STEP even though `selected_backend` records the
+  preferred semantic authoring backend for later edits.
+- `routing_policy.validation_engines`: validators required by the chosen mode.
 - Origin project and optional executable adapter.
 - `runner_skill`: installed Skill responsible for generation.
 - Ranked backend scores and human-readable reasons.
@@ -81,6 +85,11 @@ distillation corpus. The task publishes the independent DesignIR, reconstructed
 STEP, validated parameter catalog, geometry report, edit report, and
 `cad-task.json`. The reconstruction subprocess receives no teacher STEP path;
 only extraction and acceptance may read the explicit uploaded source.
+The acceptance stage records both SurfaceIR geometry validation and the
+SimpleCADAPI B-Rep comparator. A B-Rep report may be `passed`, `mismatch`, or
+`unavailable`; only `passed` earns the `brep_exact` quality tier. Geometry
+equality with a topology mismatch remains usable for review but is not an exact
+reconstruction.
 
 ## Backend adapter requirements