It was all going so well. I tested forward and brake for both channels and it was working perfectly.
That is the magic smoke being released from the left braking mosfet. It was quite the event and I can tell you that mosfet never gave up.. it was positively glowing before I cut power. Perhaps I should have actually included the fuses in the test. :)
Somehow it seems to have taken the two drive mosfets with it during its demise. So it seems I will need to rebuild half of my board here to fix it. Ugh.
I have since discovered that the 2N3904 transistors I picked to drive my braking P channel mosfets have two different ratings online. One group is rated for 40v, the other for 60v. My battery voltage maxes out at 42v, so can only assume I have the cheaper ones. I am driving the P channel via a voltage divider to keep the gate voltage within the max Vgs of my mosfet here, so I'm basically left with that.
Currently rebuilding it with spade connectors, and seeing if I have some higher voltage rated NPN transistors here. Cross your fingers.