Placing stops at beginning of combat after combat phase has already started
I had a scenario today where an opponent had an effect to tap my creature on my turn to prevent it from attacking, but I had an instant to untap it. After they used that effect, I placed a stop on the current step, with the expectation that I would hold priority once the stack was empty and could cast my instant before declaring attackers. However, the UI lumps the beginning of combat and declare attackers steps together, and when the stack was empty, I was immediately prompted to declare attackers, with no opportunity to meaningfully cast my instant.
I would suggest either of the following improvements:
A) In combat, add a separate visual marker for the beginning of combat step, distinct from the declare attackers step's marker. (This would be the most preferred fix, but would require some UI work.)
B) When a stop is placed on the declare attackers step while in the beginning of combat step, apply that stop during the beginning of combat step. (This is not as good of a fix in my opinion, but it can be enacted without any UI changes.)