A great part of Head To Head, is that you can take control of the AI, and have a more diverse interaction with the other player. But for most factions, you can't issue a military alliance.
Mulling this script over in my head, which is a bit of a deadend since the documentation for Total War is pretty lacking. I've gotten this far: https://pastebin.com/RnTdMkHY
That script should work, if it had an event that listened for the beginning of a player's turn. But I can't find a list of them anywhere.
The goal of the script is basically:
On first player turn start -> Get player 1 faction -> On second player turn start -> get player 2 faction -> On second player turn end -> Enable alliance diplomacy for both player factions -> Unregister turn start event -> Unregister turn end event
Any idea how I can achieve this? And how do I get this script to run in the game?