I've looked into HSMs and I don't think they are intended to handle this scenario due to the needed to be in multiple states at once.

For instance, you partially fill one trade. This spawns a process which must then enter an offsetting trade for that partial amount.

While this is going on, you may partially fill more of your initial trade, which then must spawn an offsetting trade for that amount (and so on).

This quickly escalates out of control when you consider all of the possibilities which can happen at each state along the way (partial fills, cancels, connection issues, circuit breakers).