I had considered that, but decided it was unnecessary. The reason is that you should just send a WINDOW_UPDATE with stream id 0 with whatever delta to increase the session window size accordingly. In order to shrink it, you just let the sender send data and don't send WINDOW_UPDATE for the session window until it goes below the desired size.

The reason to prefer a SETTINGS frame is just for persistence. I don't think we're considering persisting it as of yet.

I did consider whether or not to rename the SETTINGS id to indicate it's only for the stream window. I can do that if desired.