FINALLY figured out how to get my zsh prompt to indicate whether I'm in insert or command mode (editor = vi). Still can't find the documentation on the module I'm using, but experimentation showed me what I needed. I only discovered the module because I found someone else's dotfiles and they were using it. Thanks for sharing your dotfiles, random internet stranger.
https://github.com/benhamill/dotfiles/blob/master/prompt_ben_setup if anyone's interested.