feat: unify CAD workflows on DesignIR 3.0

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

@@ -70,14 +70,17 @@ Write `cad-task.json` beside the task artifacts with this minimum shape:
 
 Paths are relative to the task directory unless an external input must remain absolute.
 Do not store authoritative model parameters in `cad-task.json`. Every part must
-have a sibling `*.designir.json` that owns its coordinate system, datums,
-parameters, expressions, features, constraints, edit interface, and validation
-contract. See `designir-2.0.md`.
+have a sibling `*.designir.json` as its editable source of truth. Authored
+feature models use semantic DesignIR 3.0; uploaded STEP reconstruction uses
+DesignIR 3.0 / SurfaceIR. See `designir-3.0.md`; `designir-2.0.md` is retained
+only for legacy migration.
 
-For an uploaded STEP, keep teacher geometry in `designir-pipeline/input/` and
-all private evidence, DesignIR candidates, rebuilds, and acceptance reports in
-`designir-pipeline/runs/`. The reconstruction task receives evidence but no
-teacher STEP or imported B-Rep.
+For an uploaded STEP, use `scripts/route.py --execute` with an explicit source
+and task directory. Do not move an ordinary upload into or scan the
+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.
 
 ## Backend adapter requirements