Plug the URL into makeApplication with Mirror.routing

Foldkit's makeApplication takes init(url), update and routing: { onUrlRequest, onUrlChange }. Mirror.routing takes the application's own three and gives back the same three, with the mirrors reading every URL, so the result spreads straight into the runtime config. The Message gains the link variant Foldkit's routing asks for:

import { Runtime } from 'foldkit'
import { UrlRequest } from 'foldkit/navigation'

const Message = defineMessageUnion({
  ClickedLink: { request: UrlRequest },
  UrlChanged: { url: Url },
})

const routed = Mirror.routing({
  mirrors: [Filters],
  urlChanged: 'UrlChanged',
  init: (url: Url) => ({ model: initial }),
  update: (model: Model, message: Message) => ({ model }),
  routing: {
    onUrlRequest: request => Message.ClickedLink({ request }),
    onUrlChange: url => Message.UrlChanged({ url }),
  },
})

Runtime.makeApplication({ Model, ...routed, view, subscriptions, container })

What each piece does, and does not do:

• init calls the application's init and reads the starting URL into the Model it returns. The application's Commands are its own; they were made before the URL was read, so an init whose Commands depend on the slice calls Filters.reduce itself.
• update reads a UrlChanged Message's URL into the Model, then hands the Message to the application's update, which routes the path over slices the mirrors have already read. Every other Message goes straight through.
• routing is the application's own: its links, its URL Message. Nothing is intercepted or added.
• Writing the URL is still Filters.subscriptions, spread into the application's Subscriptions as above.

urlChanged names the tag the mirrors read; it must be the Message onUrlChange makes, and that Message must carry a url, or the call does not compile. A UrlChanged for the URL the Model already shows (the mirror's own write, answered by Foldkit) returns the Model it was given, provided the application's update also returns its Model for a route that did not change. examples/foldkit/query-sync is the full application.