/**
 * Push a history entry when modal opens.
 */
export function pushModalHistoryState(onBackButton: any): void;
/**
 * Clean up history state when modal closes normally.
 */
export function cleanupModalHistoryState(): void;
/**
 * Synchronize the modal to the visual viewport.
 * This is the "Best Fix" for satisfying the following requirements:
 * 1. Open diagram in perfect 1:1 scale even if background is zoomed.
 * 2. Persist background zoom and scroll position on close.
 * 3. Work reliably in Firefox, Chrome, Safari, and Brave.
 *
 * APPROACH: "Scale-Free" — position:fixed + exact visual viewport dimensions.
 *
 * We size the modal to the visual viewport (vv.width × vv.height) and
 * position it using vv.offsetLeft/offsetTop with translate3d only — NO
 * scale() transform on the modal.
 *
 * Why this matters:
 * - Panzoom operates in the modal's CSS pixel space. If we counter-scale
 *   the modal (old approach: scale(1/vv.scale)), Panzoom's coordinate
 *   space is inflated, making pan/zoom feel sluggish when the browser
 *   is pinch-zoomed.
 * - Firefox computes pageLeft/pageTop differently from Chrome when using
 *   position:absolute, causing layout shifts. position:fixed with
 *   offsetLeft/offsetTop is consistent across browsers.
 */
export function startVisualViewportSync(): void;
/**
 * Stop synchronization and cleanup listeners.
 */
export function stopVisualViewportSync(): void;
/**
 * Reset all module-level state.
 */
export function resetViewportState(): void;
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