Goval is replit's code execution API, it is used by the workspace to connect with running containers. It handles everything from the keystrokes entered in files or the shell to history. There is a debug panel in the workspace that can be enabled by adding the ?debug=1 query parameter. This will add an alien icon to the tool list, that that lets you see all messages, and even change the goval server url. You can read more about it here.
Goval uses Google's protobuf format, the last published version of govals protocol can be found at replit/protocol on github1. The npm package however, is still updated.
In the past there was a closed-alpha developer program for goval. It has since been removed, and its future is unknown. Old documentation from it can be found here, while this documentation is out of date, some of it is still relevant.
This site is unofficial, if you have found any issues please dm PotentialStyx#2158 on discord.
1 A more up-to-date version that was detranspiled from the npm package is available here.