So my Warrior Tripped. As long as he's standing still, I figured I'd have him play Shift, Team! which says "All other allies may move 1." He was prevented due to the Halt effect from Trip. Technically, Halt says "Target may not play Move cards." It is working as the rules state. However, could Shift, Team! and related cards reasonably include the line "You may play this while Halted," just like Shrug It Off says "You may play this while Stunned"? Edit: Huh, this should probably be in "feedback."
I'm inclined not to make an exception as it makes those cards much more powerful by allowing them to work around Halt states.
You can't do anything involving movement at all, I guess - if you're HALTed, you can't even play an attack card with Step on it, not even just use the attack and not Step at all. Although that's probably because you can't not use the step. Actually, that raises a question - sometimes I seem to be able to use the Step part of an attack card to rotate in place (so I can stay where I am), and other times I have to move one square and cannot simply rotate instead. I haven't tracked down which circumstances require one or the other. Jon, can you confirm, or should it always be one or the other and something odd is going on?