I'm concluding that pd runs csound (via [csound6~] ) directly in some way -- and that the instance of csound it's running does have access to the system outside the csound6~ interface:
for example, if I put a widget in the .csd file I'm playing, it normally won't get displayed. But If I put it in a widget panel in the file, it does -- not through pd, correct?
If I just wanted to use pd to send controls ( via [HID] for example), I'd expect I wouldn't need to run pd at dsp rate, could have the csound instance send audio directly to dac...