export type WidthMeasureMode = 'box' | 'scroll';
export interface WidthRegistry {
    /**
     * Returns a stable callback ref for `key`. Attach it to the element whose
     * width should be tracked. `scroll` mode measures `scrollWidth` (natural
     * content width, ignoring truncation); `box` measures the border box.
     */
    register: (key: string, mode?: WidthMeasureMode) => (element: HTMLElement | null) => void;
    /**
     * Last known width per key. Keys keep their last value after the element
     * unmounts, so variant widths (e.g. label vs icon-only) stay available
     * once each variant has been rendered at least once.
     */
    widths: Readonly<Record<string, number>>;
}
/**
 * Tracks real, rendered widths of a dynamic set of keyed elements with a
 * single shared ResizeObserver. Used by DynamicToolbar to drive layout
 * planning from measured widths instead of hard-coded estimates.
 */
export declare function useWidthRegistry(): WidthRegistry;