Alright, attached is a new attempt at this patch. Hopefully, this version is more to your liking.

Changes:
* The primary prompt can now be configured completely through `zstyle ':vcs_info:*:prompt_vcs:*’` statements.
* Accordingly, I renamed the theme to `vcs`. (Naming is hard.)
* I removed customization of the secondary prompt.
* I removed the weird shenanigans with $vcs_info_msg_0_ between chpwd & precmd. (I think I must’ve been tired when I originally wrote that code. It makes no sense to me now.)
* I added plenty of comments everywhere.

My thanks to Daniel for his thorough review and to Bart & Mikael for their zstyle/vcs_info tips. :)

Question for Daniel: If you’re going to add sysexits(3) to PRINT_EXIT_VALUE anyway (workers/48564), should I just get rid of prompt_vcs_precmd()? Or do you think it still adds value?