want a search to find card being commented on+discussion

First let's get _main out of the equation.

If search is _main+mysearch and _main is foo+comment, then search is foo+comment+mysearch. And in the context of WQL, _self would be foo+comment. So to get foo, you just need the card that is plussed to comment to create self.

WQL would be {"right_plus":["comment","_self"]}