/**
 * UndoManager — Per-Layer Slice-Snapshot Undo/Redo
 *
 * Phase 6: Replaces the old HTMLImageElement-based undo system.
 *
 * Design:
 * - Each layer has an independent undo and redo stack.
 * - Each entry (MaskDelta) stores a full 2D slice snapshot before and after
 *   the operation (cheaper than full volume, sufficient for single-stroke ops).
 * - maxStackSize: 50 entries per layer.
 * - Undo/redo operations also trigger backend sync via getMask callback.
 */
export interface MaskDelta {
    layerId: string;
    axis: "x" | "y" | "z";
    sliceIndex: number;
    /** Full slice data captured before the drawing operation. */
    oldSlice: Uint8Array;
    /** Full slice data captured after the drawing operation. */
    newSlice: Uint8Array;
}
/** A single delta or a group of deltas treated as one undo unit. */
export type UndoEntry = MaskDelta[];
export declare class UndoManager {
    private undoStacks;
    private redoStacks;
    private activeLayer;
    constructor();
    /** Set the currently active layer (determines which stack undo/redo operates on). */
    setActiveLayer(layer: string): void;
    /** Push a single delta onto the active layer's undo stack and clear the redo stack. */
    push(delta: MaskDelta): void;
    /** Push a group of deltas as a single undo unit (e.g. 3D sphere spanning multiple slices). */
    pushGroup(deltas: MaskDelta[]): void;
    /**
     * Undo the last operation on the active layer.
     * @returns The delta(s) that were undone, or undefined if nothing to undo.
     */
    undo(): UndoEntry | undefined;
    /**
     * Redo the last undone operation on the active layer.
     * @returns The delta(s) that were redone, or undefined if nothing to redo.
     */
    redo(): UndoEntry | undefined;
    canUndo(): boolean;
    canRedo(): boolean;
    /** Clear undo and redo stacks for a specific layer (called on clearActiveLayer). */
    clearLayer(layer: string): void;
    /** Clear all stacks for all layers (called on full dataset reload). */
    clearAll(): void;
}