Thank-you — `/r/{ulid}/thanks`

Who opens it: the person who just pressed submit, plus anybody they forward the link to.

What they came to do: confirm it worked, and find out what happens next.

True when they leave: they know who is registered, that an email is coming, and — if money is owed — how to pay.

Decisions already made

Its headline says the state, not a hope (Pilot Day, C5): "You're in" only once confirmed; "On the waitlist"; "Received — waiting for approval" while a decision is pending; "Received — payment still to come" when money is owed.
On the form, a full day says "— full, waitlist only", or "— closed" when it keeps no waitlist.
It lists everybody who was registered by name. "Thank you" alone does not answer the question people actually have, which is did all four of us go in.
It is the page that announces completion to an embedding group (postMessage), because a submitted form redirects here — the form itself never learns it succeeded.
It stays silent when it is not inside an iframe, so a normal visit posts nothing anywhere.
It is not signed: it is reached by redirect and shows nothing a registrant did not just type.

It says "we'll email the details soon" — which is true, and vague. Should it say when (T-12 days, per the schedule)?
An unpaid registration currently shows its state but leans on the self-service page to pay. Should paying start here?
No add-to-calendar here, only on the self-service page. This is the moment people would use it.