refactor(grasp): extract _points_via_bbox helper

Pure refactor in preparation for the SAM21 branch. _object_points_in_base
keeps its signature and the bbox→ROI→base-frame logic moves into the
private helper. Meta now includes source='bbox_roi'.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/presa_mano/api/grasp_routes.py

@@ -65,9 +65,26 @@ def _object_points_in_base(conf: float | None, class_name: str | None, sw: Stopw
         raise HTTPException(status_code=404, detail="no object detected")
     dets.sort(key=lambda d: d["confidence"], reverse=True)
     top = dets[0]
-    b = top["bbox"]
+    bbox = _bbox_to_roi(top["bbox"])
 
-    u_min, v_min, u_max, v_max = _bbox_to_roi(b)
+    pts_base = _points_via_bbox(nuwa, T_base_cam, bbox, sw)
+    meta = {
+        "detection": top,
+        "T_base_camera": T_base_cam.tolist(),
+        "n_points": int(len(pts_base)),
+        "source": "bbox_roi",
+    }
+    return pts_base, meta
+
+
+def _points_via_bbox(nuwa, T_base_cam: np.ndarray, bbox: tuple[int, int, int, int],
+                     sw: Stopwatch) -> np.ndarray:
+    """Legacy path: bbox → Nuwa ROI cloud → filter outliers → base frame.
+
+    Raises HTTPException(422) on <10 valid depth points (existing behaviour).
+    """
+    cfg = get_config()
+    u_min, v_min, u_max, v_max = bbox
     try:
         with sw.step("pointcloud_roi"):
             pc, _meta = nuwa.pointcloud_roi(
@@ -81,11 +98,10 @@ def _object_points_in_base(conf: float | None, class_name: str | None, sw: Stopw
         cropped = filter_outliers(pc)
     if len(cropped) < 10:
         raise HTTPException(status_code=422, detail=f"too few valid depth points in bbox: {len(cropped)}")
-
     with sw.step("to_base_frame"):
         pts_cv = nuwa_to_cv_frame(cropped[:, :3])
         pts_base = transform_points(T_base_cam, pts_cv)
-    return pts_base, {"detection": top, "T_base_camera": T_base_cam.tolist(), "n_points": len(pts_base)}
+    return pts_base
 
 
 @router.post("/plan")