Discarding based on Trace

[telser]

It does not appear that there is any way to discard a possible execution based on the Trace that got us there. This could be very helpful to create assertions based on some part of the execution space.

Full context of what I'm trying to do because there is likely a better way:

I have a networked service that includes some resource locking. I'd like to test with concurrent clients, A and B, such that when A wins the race for the lock and performs task T, the results are X but that when B wins the race and performs task U the results are Y. This would be regardless of interleaving between A and B, but notably the lock primitive is held in the networked service, not between A and B.

In the above I've stated things as if A and B are independent programs, but they really would be separate threads of a single program.