feat: integrate SimpleCADAPI 2.0.2 CAD workflows

text-to-cad/skills/cad-router/SKILL.md

@@ -5,7 +5,7 @@ description: Route natural-language or image-guided CAD generation and modificat
 
 # CAD Router
 
-Choose a backend before modeling, keep its source as the editable authority, and normalize every result into one handoff contract. Use two projects by role: text-to-cad owns orchestration, general CAD, refinement, validation, repair, and viewing; SimpleCADAPI owns specialized mechanical families.
+Choose a backend before modeling, keep its source as the editable authority, and normalize every result into one handoff contract. `text-to-cad` is the backend-neutral orchestrator and DesignIR owner, not a backend that must win by default. `build123d` and SimpleCADAPI 2.0.2 are equal-priority authoring backends selected from evidence. Uploaded STEP reconstruction is executed by SurfaceIR and independently checked by both the existing geometry validator and SimpleCADAPI B-Rep comparison.
 
 ## Required workflow
 
@@ -47,8 +47,8 @@ Choose a backend before modeling, keep its source as the editable authority, and
    publication. A route decision alone is not a completed reconstruction.
 3. Follow the selected route unless a hard environmental constraint makes it unavailable. If overriding it, record the reason in the task manifest.
 4. Load only the selected backend reference from `references/capabilities.md` and the matching installed Skill:
-   - `build123d`: use `$cad`; this is the default for general STEP-first mechanical parts, assemblies, and existing STEP modification.
-   - `simplecadapi`: use an installed SimpleCADAPI Skill/runtime; prefer it for gears, racks, ring gears, bearings, cycloidal parts, reducers, replayable graphs, and semantic tags.
+   - `build123d`: use `$cad`; prefer it for custom brackets, housings, shafts, flanges, fixtures, source-level assemblies, and freeform/custom surface work.
+   - `simplecadapi`: use an installed SimpleCADAPI 2.0.2 Skill/runtime; prefer it when a standard factory exists, or when replayable ModelResult graphs, semantic lineage, physical units, tolerance chains, scene packages, or CAD translators materially improve the result. Its standard library includes gears, racks, ring and bevel gears, bearings, bolts, nuts, roller-chain sprockets, cycloidal parts, and reducer families.
 5. When the route reports `requirement_refinement` or `visual_repair`, refine the brief, generate, execute, inspect multiple views, and repair no more than three visual mismatch rounds before asking the user.
 6. Generate into a task-owned directory and start CAD Viewer with that task directory as `--dir`; do not expose the repository-wide fixture library for a task review. Write one DesignIR 3.0 `*.designir.json` per part and treat it as the editable geometry contract; keep `cad-task.json` as the execution record. Read `references/designir-3.0.md` for both semantic authoring and uploaded STEP reconstruction. `references/designir-2.0.md` is migration-only. Never change backend during an edit unless conversion is explicitly requested; modify the recorded authoritative layer.
    For a supplied STEP/STP, use `scripts/route.py --execute`; do not manually
@@ -60,21 +60,39 @@ Choose a backend before modeling, keep its source as the editable authority, and
    The DesignIR and generator must not import STEP, embed B-Rep or meshes, retain
    face references, or use the source model as a base feature. The acceptance
    agent alone compares the teacher and reconstructed STEP.
+   Dense SurfaceIR may be stored losslessly in the DesignIR 3.0
+   `gzip+base64+json` envelope. CAD runtimes verify and decode it; LLM prompts
+   receive only the semantic layer, edit interface, and validated parameter
+   catalog, never the encoded geometry payload.
    Only expose parameters listed by `parameters.json`; every listed parameter
    has passed an isolated perturbation test. Other inferred names remain
    evidence, not a promised edit interface.
+   The acceptance zone also runs the installed SimpleCADAPI 2.0.2 strict B-Rep
+   comparator. `brep_exact` requires both the bidirectional geometric-set check
+   and the geometry-labelled incidence graph check. A geometry-equal but
+   topology-different result is returned as `review_required`, not silently
+   described as an exact reconstruction. Failure or absence of the supplemental
+   comparator must be recorded separately and must not be confused with a pass.
 7. Validate against the brief. Run STEP geometry inspection and snapshot review.
    For experience-informed generation, record which generalized methods were
    applied, including the reconstruction grammar ID and instantiated symbolic
    roles. Validate against the user's brief and held-out targets, never against
    parameters exposed from the same source case.
 8. Write a `cad-task.json` manifest using the contract in `references/backend-contract.md`. Hand the STEP artifact to `$cad-viewer` and return its live link.
+9. Export URDF or MJCF only on explicit request. Run the deterministic
+   DesignIR robot-description exporter lazily and return its portable ZIP with
+   XML, STL visual/collision geometry, and export manifest. When authoritative
+   assembly/joint/material evidence is absent, export one fixed `base_link`;
+   never invent joints, limits, actuators, mass, or inertia.
 
 ## Routing rules
 
 - Prefer an explicit user backend when it can produce the editable STEP contract.
-- Prefer SimpleCADAPI when a supported standard mechanical factory or replay/semantic requirement materially reduces custom modeling.
-- Prefer build123d for general machined parts such as brackets, connecting rods, housings, shafts, flanges, fixtures, and source-driven assemblies.
+- Preserve the backend of an explicitly supplied DesignIR or Python generator unless conversion is requested.
+- Do not assign a permanent default backend. Score native-source continuity, factory coverage, semantic/replay needs, geometry vocabulary, assembly needs, and validation needs.
+- Prefer SimpleCADAPI when a supported standard mechanical factory or its model graph, semantic topology, unit/tolerance, scene, or translator capabilities materially improve editability and verification.
+- Prefer build123d for custom machined parts, source-driven assemblies, and freeform or surface-heavy work not covered by a SimpleCADAPI factory or tested operation vocabulary.
+- For uploaded STEP, report SurfaceIR as the effective reconstruction engine. The selected authoring backend describes future semantic repair/edit work; it is not allowed to read the teacher STEP during reconstruction.
 - Prefer source quality and future modification over the shortest first generation.
 
 ## V1 boundaries