Planechase - Planar Die timing not correct

While I'm submitting issues, I saw one when I was playing Planechase against madbot the other day. Three players, and on every one of my first mains, usually in response to something, it would activate the ability. No idea how that works because it breaks every rule of the Planar Die.

Start by reproducing a Planechase game with three players against madbot, focusing on the Planar Die ability activating during the first main phase. Trace when the ability is triggered relative to game actions and responses; done means its timing follows the Planar Die rules.

Written by the indexing model from the issue text.