/**
 * PNG export for the Schema Builder canvas.
 *
 * Reference: `docs/plans/20260501-universal-wysiwyg-schema-ux-v1.00W.md`
 * §3.6 item 8.
 *
 * Uses `html-to-image` against a DOM element (typically the React Flow
 * `.react-flow` wrapper) to produce a high-DPI PNG data URL, then triggers a
 * browser download via an invisible anchor element.
 *
 * The `filter` callback strips the minimap, controls, and floating toolbar
 * overlays so the exported image shows only the pure schema diagram (matching
 * user expectation from Figma / dbdiagram).
 */
/**
 * Default filename derived from the current timestamp. Colons/dots are
 * replaced so the filename is valid on Windows filesystems.
 */
export declare function defaultPngFilename(): string;
/**
 * Render the given element to a PNG and trigger a download.
 *
 * @param element - DOM element to snapshot (typically `.react-flow` wrapper).
 * @param filename - Optional filename. Defaults to `schema-<ISO-timestamp>.png`.
 * @returns a promise that resolves once the download has been initiated, or
 *   rejects if the snapshot fails. Callers should surface rejection to a toast.
 */
export declare function exportCanvasToPng(element: HTMLElement, filename?: string): Promise<void>;
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