audio DSP nodes advertise no params
audio-dsp nodes (which are in fact, spa audioconvert) have no params listed as available in pipewire-cli. However, the code clearly shows that you can set profiles and properties such as volume/mute, and in fact they work if you set them.
Also, when you set the params (for instance, setting the volume prop), there is no change notification on clients that have subscribed with subscribe_params().
It looks like audioconvert should advertise a spa_node_info and also listen for changes to the underlying spa node's info and propagate them.