[`MJX`] `data.cfrc_ext` is missing

[Kallinteris-Andreas]

Hi,

I'm a maintainer of Gymnasium & Gymnasium-Robotics, and I'm trying to use MuJoCo-MJX for "prototyping MJX-based RL environments in Gymnasium".

data does not seem to have the cfrc_ext member variable, is named something else or is it missing? The documentation does not indicate it would be missing https://mujoco.readthedocs.io/en/3.0.1/mjx.html#feature-parity

Here is the model tested: Gymnasium/Ant (though it should not matter for the question)

Thanks!

[yuvaltassa]

This will be added when sensors are implemented (this field is required for force/torque sensors), so it's "mentioned" in Feature Parity because Sensors are in the "Under Development" section.