Splitting from this discussion:
I know this discussion has come up a few times and not made much progress, but we currently have people actively willing to help create a ClassicPress Codex/Developer handbook and think we need to get a decision made and some progress made.
I know there is a Docs site on GitHub, but the tools available to automatically generate a Codex produce HTML output and, to take take advantage of these tools, we should be looking at a ClassicPress site on a subdomain which will allow us to use those tools to automate the process rather than trying to reinvent the wheel.
I reference the WordPress Codex quite a bit, but as it will be diverging from ClassicPress with the new functions and so on created for blocks. we need one based off the ClassicPress codebase.
We can get this done fairly quickly using existing tools if we go with a subdomain site; if we have to create tools to generate Git compatible markdown it will take a long time and (possibly/probably) never actually happen.