Restore before the first render with bootstrap

A key-value mirror normally restores asynchronously: restore reads the store and its MirrorRestored arrives later through update, leaving the first render on defaults. When the store's keys are already in hand at boot — Flags the server embedded in the page, a synchronous read, a test fixture — fold them into the initial Model instead, with no Command and no flash:

import type { Encoded } from 'foldkit-mirror'

const init = (flags: { prefs: Encoded }, url: Url): Return => ({
  model: Mirror.bootstrap(
    initial,
    Prefs.bootstrap(flags.prefs),
    model => Filters.reduce(model, url),
  ),
})

What each piece does, and does not do:

• Prefs.bootstrap(keys) is a pure step applying pre-read keys to the fields still at their initial value — the same conservative read reduce applies to a MirrorRestored, run before the first render instead of after a Command. It sends no Message and runs no Effect.
• model => Filters.reduce(model, url) is the URL mirror's step: the starting URL as the whole slice, the same call Mirror.routing folds into makeApplication's init.
• Mirror.bootstrap(model, ...steps) folds the steps in list order: stores first, the URL last. Either order keeps URL > store > initial, but listing the URL last states the precedence.

A step that changes nothing returns the Model it was given, so an empty store renders nothing extra. Flags carry the store's keys as the store holds them (Encoded: Record<string, string>), and the mirror decodes them with its own codecs — the Flags schema does not repeat the text format.

When the store can only be read asynchronously, keep the restore Command (Prefs.wiring()'s init, foldPrefs.init): bootstrapping needs the keys, and restore is how they arrive. A bootstrapped value also wins over a later restore for the fields it set, and the usual Subscription writes it outward like any Model change — so bootstrapping from Flags while still running restore is safe, not a conflict.

This is deliberately not part of Wiring: Wiring.init runs startup Commands after the Model exists, while a bootstrap runs before it, inside init itself. One is Bootstrap / Flags into the initial Model; the other is the Model into Commands.