The harness isn't either of those; the harness is quite literally a harness, giving the model/agent sensors and actuators (aka "skills") to interact with its environment. Compare with e.g. the Power Loader from Aliens: https://www.deviantart.com/pynion/art/Aliens-Power-Loader-11...
The model is still the model, and the agent is still the user<->model interface.
The model is still the model, and the agent is still the user<->model interface.