docs: add generation pipeline, 3MF export, and download panel to planning spec

docs/superpowers/specs/2026-04-12-planning-review-gate-design.md

@@ -374,35 +374,203 @@ When the scoring threshold triggers in chat mode, an interactive plan card appea
 - Only one plan card active at a time
 - All labels go through `I18N` / `t()` for i18n support
 
-## Files Changed
+## Generation Pipeline (Post-Approval)
+
+When `phase == "approved"` and the chat turn runs with CAD + CNC agents, the orchestrator executes a full generation pipeline. This is not a new pipeline — it's the existing flow, but now it only runs after explicit user approval.
+
+### Generation Steps
+
+```
+Plan approved (phase = "approved")
+    |
+    v
+1. CAD GENERATION
+   - CAD agent receives approved plan in context
+   - Generates CadQuery code
+   - Executor runs code -> cq.Workplane result
+   - Geometry metadata extracted (volume, bbox, faces, edges)
+   |
+   v
+2. EXPORT 3D FILES
+   - STEP export: output/{part_name}.step (precision CAD format)
+   - STL export:  output/{part_name}.stl  (mesh for 3D preview)
+   - 3MF export:  output/{part_name}.3mf  (slicer-ready format)
+   |
+   v
+3. CNC VALIDATION
+   - Manufacturability check (wall thickness, pocket depth, undercuts)
+   - Axis recommendation (3-axis / 3+2 / 5-axis)
+   - Issues list (errors + warnings)
+   |
+   v
+4. CAM / G-CODE GENERATION
+   - CAM agent creates machining plan (operations, tool config, post-processor)
+   - core/cam.py generates G-code from shape + plan
+   - G-code saved to output/{part_name}.gcode
+   |
+   v
+5. 3D PREVIEW
+   - STL loaded into Three.js viewport
+   - G-code toolpath rendered as 3D lines (if generated)
+   - View toggle: Part / Toolpath / Overlay
+   |
+   v
+6. DOWNLOADS AVAILABLE
+   - All export files served and download buttons shown
+```
+
+### 3MF Export (New)
+
+CadQuery supports 3MF via OCCT. Add `export_3mf()` to `core/executor.py`:
+
+```python
+def export_3mf(result: cq.Workplane, path: str | Path) -> Path:
+    """Export a CadQuery workplane to 3MF format (slicer-ready)."""
+    path = Path(path)
+    cq.exporters.export(result, str(path), exportType="3MF")
+    return path
+```
+
+Update `export_all()` to include 3MF:
+
+```python
+def export_all(result: cq.Workplane, base_path: str | Path) -> dict[str, Path]:
+    """Export to STEP, STL, and 3MF."""
+    base = Path(base_path)
+    return {
+        "step": export_step(result, base.with_suffix(".step")),
+        "stl": export_stl(result, base.with_suffix(".stl")),
+        "3mf": export_3mf(result, base.with_suffix(".3mf")),
+    }
+```
+
+### New Endpoint: GET /api/models/{name}.3mf
+
+```python
+@app.get("/api/models/{name}.3mf")
+async def get_3mf(name: str):
+    path = OUTPUT_DIR / f"{name}.3mf"
+    if not path.exists():
+        return JSONResponse({"error": f"3MF not found: {name}"}, status_code=404)
+    return FileResponse(path, media_type="model/3mf", filename=f"{name}.3mf")
+```
+
+### Updated Preview Response
+
+The preview response returned after generation includes all file URLs:
+
+```json
+{
+    "success": true,
+    "part_name": "bracket",
+    "stl_url": "/api/models/bracket.stl",
+    "step_url": "/api/models/bracket.step",
+    "threemf_url": "/api/models/bracket.3mf",
+    "gcode_url": "/api/models/bracket.gcode",
+    "execution": {
+        "success": true,
+        "volume_mm3": 48000,
+        "bounding_box_mm": [60, 40, 20],
+        "face_count": 14,
+        "edge_count": 24
+    },
+    "validation": {
+        "machinable": true,
+        "axis_recommendation": "3-axis",
+        "issues": [],
+        "error_count": 0,
+        "warning_count": 0
+    },
+    "cam": {
+        "success": true,
+        "operations": ["adaptive", "profile"],
+        "tool_config": {"diameter": 6, "h_feed": 800, "v_feed": 200, "speed": 18000},
+        "post_processor": "grbl"
+    }
+}
+```
+
+### Download Panel (Updated)
+
+The existing download buttons panel gains a 3MF button and is reorganized by purpose:
+
+```
++------------------------------------------+
+|  DOWNLOADS                               |
+|                                          |
+|  3D Files:                               |
+|  [STEP]  [STL]  [3MF]                   |
+|                                          |
+|  CNC Files:                              |
+|  [G-CODE]                                |
+|                                          |
+|  Documentation:                          |
+|  [REPORT]                                |
++------------------------------------------+
+```
+
+- **STEP** — precision CAD interchange format (for CAD software)
+- **STL** — triangulated mesh (for 3D printing, basic viewing)
+- **3MF** — slicer-ready format (for Cura, PrusaSlicer, Bambu Studio)
+- **G-CODE** — CNC machining program (only visible when CAM has run)
+- **REPORT** — design report JSON
+
+Each button is only visible when its corresponding file exists. The G-CODE button remains hidden until CAM generation succeeds. The 3MF button is always shown alongside STL (both are generated by `export_all`).
+
+### Gallery Card Downloads
+
+Gallery cards also updated to show all available formats:
+
+```html
+<div class="gallery-card-downloads">
+    <a href="/api/models/{name}.step" download>STEP</a>
+    <a href="/api/models/{name}.stl" download>STL</a>
+    <a href="/api/models/{name}.3mf" download>3MF</a>
+    <a href="/api/models/{name}.gcode" download>GCODE</a>
+</div>
+```
+
+### 3D Preview Behavior
+
+After generation, the 3D viewer automatically:
+1. Loads the STL into the Three.js viewport
+2. If G-code exists, parses and renders toolpath lines (existing G-code preview feature)
+3. Shows view toggle buttons: Part / Toolpath / Overlay
+4. Shows geometry stats (volume, bounding box, face count)
+5. Shows CNC validation badge (machinable / warnings / errors)
+
+## Files Changed (Updated)
 
 | File | Change |
 |------|--------|
 | `agents/design_state.py` | Add `phase`, `plan` fields to `DesignState`; add `DesignPlan` model; add `compute_score()` function |
 | `agents/crew_orchestrator.py` | Add phase branching, plan generation, plan trigger keyword detection, approved-phase context injection, routing override |
-| `agents/base.py` | No changes (interface unchanged) |
 | `config/settings.py` | Add `PlanningConfig` model, add `planning` field to `Settings` |
 | `config/config.yaml` | Add `planning` section with threshold, weights, caps, keywords, approved_agents |
-| `server/routes.py` | Add `POST /api/plan/approve` and `POST /api/plan/reject` endpoints; add `PlanApproveRequest`, `PlanRejectRequest` models |
-| `web/index.html` | Add tab switcher, guided wizard UI, plan card component, state sync logic, i18n entries |
+| `server/routes.py` | Add `POST /api/plan/approve` and `POST /api/plan/reject` endpoints |
+| `server/web.py` | Add `GET /api/models/{name}.3mf` endpoint |
+| `core/executor.py` | Add `export_3mf()` function; update `export_all()` to include 3MF |
+| `web/index.html` | Add tab switcher, guided wizard UI, plan card component, state sync, download panel with 3MF button, gallery card 3MF download, i18n entries |
 
 ## Files Not Changed
 
 | File | Reason |
 |------|--------|
 | `agents/orchestrator.py` (MockChatBackend) | Mock backend does not need planning — it's for testing only |
+| `agents/base.py` | Interface unchanged |
 | `agents/routing.py` | Routing logic unchanged; override happens in orchestrator |
 | `agents/definitions.py` | No new agents |
 | `agents/tools.py` | No new tools |
-| `core/executor.py` | Execution pipeline unchanged |
 | `core/validator.py` | Validation unchanged |
-| `core/cam.py` | CAM pipeline unchanged |
+| `core/cam.py` | CAM pipeline unchanged — already generates G-code when CAM agent is active |
 
 ## Testing Strategy
 
 - **Unit tests for `compute_score()`** — verify scoring with various `DesignState` configurations, cap behavior, threshold edge cases
 - **Unit tests for plan generation** — verify `DesignPlan` is correctly synthesized from `DesignState`
 - **Unit tests for phase transitions** — verify all state machine transitions (exploring->planning->approved, approved->exploring on NOT READY, etc.)
+- **Unit tests for `export_3mf()`** — verify 3MF export produces valid file
 - **Integration test for `chat_turn` with planning** — verify auto-trigger when score crosses threshold, verify manual trigger via keywords, verify approved phase routes to CAD+CNC
-- **API tests** — verify `/api/plan/approve` and `/api/plan/reject` endpoints
-- **Frontend manual testing** — tab switching, wizard step navigation, state sync between tabs, plan card approve/reject, i18n
+- **Integration test for generation pipeline** — verify that approved phase produces all outputs: STEP, STL, 3MF, G-code (when CAM active), validation results
+- **API tests** — verify `/api/plan/approve`, `/api/plan/reject`, and `/api/models/{name}.3mf` endpoints
+- **Frontend manual testing** — tab switching, wizard step navigation, state sync between tabs, plan card approve/reject, download buttons visibility (STEP/STL/3MF always, G-CODE only after CAM), gallery card downloads, i18n