The Principles page has a section under “Technology” titled “We reluctantly operate some infrastructure” where it describes your own notification system (instead of CloudKit).

But later on in the same page, the following promise is made under the “Harm Reduction” section:

> Straight to Apple servers. Tact does not store your messages, files, photos, or any other data. They are stored only on Apple servers, and we as the makers of Tact have no access to them. We cannot provide your data to anybody even when requested or forced — we just don’t have it.

This part should have an asterisk and a link to the notifications section, since your systems will be able to see some metadata and data of the messages, and we don’t know how long that’s retained and what kind of backup systems those might end up in for a long duration.