Exchange Goal Invitation

Which model a service answers goal turns on: the tape's lane (#2317).

Read off the model the boundary actually built (:meth:~cheshire.model_clients.ModelLane.of), never derived a second time from settings, so what a recording claims and what answered it cannot drift.

The owner's goal, in one read (#1984).

The same sections as the public page (:class:GoalPageSections), plus what only the owner may act on: the goal id every write takes, the conversation's status, where the page is live, and whether an app account holds it. The public read is not a narrower page, it is the same page without the handle.

share_id/slug/published_at are StoredGoal.live_share read-only — all three together or none, the same guarantee that property already holds, not a fourth spelling of it. Settling publishes the goal (#3057), so they are set from the settle on; a goal whose page was taken down reads null.