API or database editing for import from other chat apps?

Clearly the normal API (https://developers.stoat.chat/api-reference/) is not useful for this. It assumes you're making changes as a specific user with a specific user's permissions, among other limitations.

I'm interested in implementing something that can take an export from some other chat platform and stuff it into a local Stoat server, as if the message history had always been sent through stoat. Intact messages, attachments, message-sent timestamps, etc, etc, including mapping of accounts on the old chat platform to those on the stoat server.

There doesn't seem to be any existing API for this kind of large-scale editing of history. (on eg. discord you could partially achieve this with a bot that's allowed to masquerade as other users, but you couldn't fixup the timestamps) It seems to me that in absence of such an API, the next best thing would be documentation of the current database schema and generally how it's all laid out so I could edit it directly. This does probably have breakage concerns between versions of stoat, but such is life.

If anyone does know of such documentation, or other approaches to this problem, I'd be interested. It doesn't need to be done on-line.