/**
 * The branded door treatment, injected into the HOST document.
 *
 * A door (`data-olotalk-open`, ADR 0243) is the host page's own element, and the
 * assistant's own stylesheet lives inside our shadow root, style isolation that
 * exists precisely so we never leak into an operator's page. So a door cannot be
 * reached by the CSS we already ship: branding one means putting rules in the
 * light DOM, which is a deliberate exception and is why this is opt-in.
 *
 * OPT-IN, twice over. Nothing here matches a bare `data-olotalk-open`; every
 * rule is scoped to `[data-olotalk-open][data-olotalk-door="branded"]`, which the operator (or the
 * Install snippet) puts there on purpose. ADR 0243's premise is "any element the
 * host already has", an element we restyle without being asked is not that.
 *
 * The sheet is installed once per page on first mount, unconditionally, rather
 * than after scanning for a door. A stylesheet already in the document styles
 * elements added later for free, so a door rendered by a framework re-render or
 * a nav that hydrates after us needs no re-scan, the same reasoning that makes
 * the click handler delegated. On a page with no branded door the selectors
 * match nothing and cost nothing.
 *
 * CSP: a constructed stylesheet is script-driven, so it is not subject to
 * `style-src` the way an inline `<style>` is. Operator pages with a strict CSP
 * are exactly where our branding has been dropped before, so the constructable
 * path is tried first and the `<style>` element is the fallback. If both fail
 * the door is unstyled, it still opens, which is the part that matters.
 *
 * No shadow, at rest or on hover (founder, 2026-08-19): the moving rim is the
 * entire hover affordance, and a glow under it competed for the same attention.
 *
 * ⚠️ The palette below duplicates `--ot-door-*` in `packages/styles/variables.css`
 * and the rim constants in `Assistant.svelte`. That is forced, not sloppy: this
 * bundle ships onto pages that never load `@olotalk/styles`, so it cannot read a
 * token. Change one, change all three. Recorded in ADR 0248.
 */
export declare function installDoorStyles(): void;