import { ConversationStreamKey } from './types';
export interface PositionCache {
    /**
     * Replaces the ordered key list; measured heights survive by key, but only
     * for keys still present (plus `retain`). Pruning here is what keeps a
     * reused instance honest when the host swaps datasets: ids that repeat
     * across datasets ("user-1" in every thread) must not inherit another
     * dataset's measurements. `retain` shields the live row, which is measured
     * before its key ever appears in this list.
     */
    syncKeys: (keys: ConversationStreamKey[], retain?: ConversationStreamKey | null) => void;
    /**
     * Records a measured height and returns the delta against what the layout
     * previously assumed — the caller compensates scrollTop with it when the
     * item sits above the viewport.
     */
    setHeight: (key: ConversationStreamKey, height: number) => number;
    heightOf: (key: ConversationStreamKey) => number;
    /** Top offset of the item at `index`; `offsetOf(length)` is the total height. */
    offsetOf: (index: number) => number;
    totalHeight: () => number;
    /** Sum of the first `count` item heights — the prepend anchoring delta. */
    prefixHeight: (count: number) => number;
    /** Half-open `[start, end)` index range covering the viewport plus overscan. */
    visibleRange: (scrollTop: number, viewportHeight: number, overscan: number) => {
        start: number;
        end: number;
    };
}
/**
 * Height bookkeeping for a dynamic-height virtual window. Heights live in a
 * key-indexed map so a prepend — which shifts every index — never invalidates
 * a measurement; offsets are a lazily rebuilt prefix-sum over the current
 * key order.
 */
export declare function createPositionCache(estimatedItemHeight: number): PositionCache;