import { type RefObject } from 'react';
/**
 * Measures the existing Root slots that are not managed by the chat-layout allocator.
 * Only count separate inline columns: Aside stacks below Main on mobile, and the
 * legacy Panel spans other areas while overlaying. Read the grid rather than duplicating
 * its responsive breakpoints. Border boxes include slot borders and live splitter widths.
 */
export declare function useOccupiedLayoutWidth(layoutRef?: RefObject<HTMLDivElement | null>): number;