@sgrobert I discovered this limitation as well and posted about it on the forum just a few days ago. In case you’re interested:
Given this limitation, what I’m looking at doing instead of using Ghost as a headless CMS with a static site generator is using userbase.com which I haven’t used before, but it looks like it is suitable for what I need to do, which is add user accounts and some minimal data persistence to an otherwise static documentation site.