What it owns, and what it does not

It owns the handover: which slice crosses, how it is written into the page, and the checks that the browser can start from it.

• Rendering and adoption stay Foldkit's. SSR.render calls Foldkit's renderToString and SSR.hydrate calls Runtime.hydrate, which adopts the server's nodes. SSR.hydrate compares the page's build id with its own before it reads the envelope, so a Model serialized by another deployment is never decoded.
• The Model stays the application's. A plan names fields of it; it adds no state of its own, and every change after boot goes through update.
• Data belongs to its package. Remote's store crosses through Remote's own part (Remote.resume), which decides what to capture.