Appeals Committee. Disputed situations in tournaments.

A simple option for mirror match templates: make the Overkill Halt (OH) trigger after one of the players breaks through to the opponent's plane.

This isn't a simple option. On Diamond, the portal can easily be broken through on turn 112. And even on X3DM1, it's often broken through on the first turn, although this encounter isn't particularly likely.

Regarding the main topic: I believe that the current OH logic required a replay of the blue player's last turn, but Zee should have requested this immediately (it seems from the stream that he immediately understood what happened and could have not waited for the outcomes of all the battles). But by then, after the red player had already moved and won 3 battles against the blue player, the opportunity had passed. You formally agreed with what was happening as soon as you started moving in the first combat encounter.