Wouldn't ````handle-unprocessable-entity```` instead of ````#(handle-unprocessable-entity %)```` be sufficient?

I find the general idea a great improvement -- especially when you need to short-cut the decision process or handle custom status codes. However, I'm not happy with adding the check to post! as this is a action function intended for side effects only. I think it should be put before post! but there is not clear interception point.

We need to find a way for deeper re-wireing of the decision graph but that's out of scope here.