/**
 * Ensure the host page's `<meta name="viewport">` carries `viewport-fit=cover`
 * while the mobile chat panel is open.
 *
 * Without `viewport-fit=cover`, iOS Safari clips `position: fixed` elements to
 * the layout viewport, which EXCLUDES the bottom safe-area / home-indicator
 * inset. No matter how tall the opaque backdrop is, host-page content shows
 * through that strip. `viewport-fit=cover` lets the overlay paint edge-to-edge.
 *
 * The change is reversible: the original meta `content` is restored (or the
 * meta we created is removed) when the panel closes.
 */
/**
 * Pure helper: given an existing viewport meta `content` (or null when there is
 * no meta), return the content string that includes `viewport-fit=cover`.
 */
export declare function withViewportFitCover(content: string | null): string;
/** Apply `viewport-fit=cover` to the host page (idempotent, reversible). */
export declare function enableViewportFitCover(): void;
/** Undo {@link enableViewportFitCover}. */
export declare function restoreViewportFit(): void;