Capture mjs_attach error message in the Python bindings.

PiperOrigin-RevId: 682409212
Change-Id: I391ee48626e7dcd985f65a231370ef5ec16124d7

src/user/user_api.cc

@@ -521,13 +521,20 @@ mjsDefault* mjs_addDefault(mjSpec* s, const char* classname, const mjsDefault* p
 
 
 
-// get objects
+// get spec from body
 mjSpec* mjs_getSpec(mjsBody* body) {
   return &(static_cast<mjCBody*>(body->element)->model->spec);
 }
 
 
 
+// get spec from frame
+mjSpec* mjs_getSpecFromFrame(mjsFrame* frame) {
+  return &(static_cast<mjCFrame*>(frame->element)->model->spec);
+}
+
+
+
 // find spec (model asset) by name
 mjSpec* mjs_findSpec(mjSpec* s, const char* name) {
   mjCModel* model = static_cast<mjCModel*>(s->element);

src/user/user_api.h

@@ -188,6 +188,9 @@ MJAPI mjsMaterial* mjs_addMaterial(mjSpec* s, mjsDefault* def);
 // Get spec from body.
 MJAPI mjSpec* mjs_getSpec(mjsBody* body);
 
+// Get spec from frame.
+MJAPI mjSpec* mjs_getSpecFromFrame(mjsFrame* frame);
+
 // Find spec (model asset) by name.
 MJAPI mjSpec* mjs_findSpec(mjSpec* spec, const char* name);