Cairn is a private chat. Your goal, your notes, your steps and your letters live in one folder of your own on the service's server. Other people who use Cairn never see it, it is not sold, and it is not used to advertise anything to you.
What is kept: the goal and month mark you set, the milestones you approve, the notes you send (text, and voice notes transcribed into text), your plan and step state, and small preferences like the hour you chose and how often you want to be checked in on. That is the whole list.
Outside services are involved. Telegram carries your messages, the same as any Telegram chat. An AI service writes some replies (answers to questions, milestone proposals, small step breakdowns, and your Sunday letters), and the text needed for that reply is sent to it for that moment. And payments, when they begin, run through Stripe, with card details never touching Cairn.
Who reads it: the service itself, to do the things you asked for, like check-ins and letters. Nobody else reads your folder, and the maker does not browse it. If you write through the contact form, the message you send is used to help you and nothing more.
You can export everything or wipe everything from inside the chat, at any time, instantly. Wiping is real: your notes are removed from the service, not hidden. Encrypted backups of the service exist for disaster recovery, are kept for about two weeks, and roll off on their own; wiped data falls out of them as they age.
Questions about any of this go through the contact form.