Strictly speaking, this may not belong here,* but it peeves me summat rotten that I don't know the answer:

If B thinks doing X will help A, then discusses it with A before doing it, it's a conspiracy.

If B thinks doing X will help A, and does X anyway without asking, what is it? "Collusion" is a milder synonym for conspiracy, so it ain't that; the nearest I can get is "aiding without abetting", which is ugly, or "giving aid and succour", which is needlessly legalistic.

I open the query to the floor. Have at it, gentlecatters.

* And I may well have asked this elsewhere already. I blame bit rot in the wetware.