Thanks a lot for the detailed feedback! You are right, I completely forgot to mention anywhere that the opponent can curse too - welp!
The king being able to move into unsafe squares is both by design and by lack of time. I was going to add it in, but kinda felt that the game did feel more "cursed" if the King could die. This resulted in a design shift to make the game about scoring points rather than winning, but the higher pieces of course grant more points if they survive the game.
I was not able to implement the promotion and en passant. And frankly, I didn't even remember castling while implementing chess... I will definitely be adding those in a post-jam version of the game.
Thanks again for the detailed feedback, appreciate it a lot!