Do not namespace the body that contains the frame during mjs_attachFrame.

PiperOrigin-RevId: 730912252
Change-Id: I026993af648766c09d569709d268430207d83169

src/user/user_objects.cc

@@ -917,8 +917,10 @@ mjCBody& mjCBody::operator+=(const mjCFrame& other) {
   CopyList(lights, subtree->lights, fmap, &other);
 
   if (!model->deepcopy_) {
+    std::string name = subtree->name;
     subtree->SetModel(model);
     subtree->NameSpace(other_model);
+    subtree->name = name;
   }
 
   int nbodies = (int)subtree->bodies.size();

test/user/user_api_test.cc

@@ -1193,6 +1193,9 @@ TEST_F(MujocoTest, AttachFrame) {
   // check that the spec was copied
   EXPECT_THAT(mjs_findSpec(parent, "child"), NotNull());
 
+  // check that the parent body was not namespaced
+  EXPECT_THAT(mjs_findBody(child, "world"), NotNull());
+
   // compile new model
   mjModel* m_attached = mj_compile(parent, 0);
   EXPECT_THAT(m_attached, NotNull());