Well, to be picky about it, a Wound prevention flip technically happens before Wds are inflicted. There is this whole thing on the forum about how if your prevention flip brings wounds to 0 then you suffer no wounds instead of 0 wounds, and any effects that rely on after damaging fail. That's a whole other bunch of stuff though
The rules manual sez
Meanwhile the Guardian's Protect spell states
So I think the timing is Prevention Flip, and then the effects from Protect resolve.
tl;dr Stone then Gaurdian.