/**
 * Display-resolution cache for frame screenshots. Captures are taken above
 * 1:1 so zoomed frames stay sharp, but an overview showing every frame keeps
 * the full decoded bitmaps resident — gigabytes for a large storyboard, and
 * the canvas pans like it is buffering. When the camera draws below one
 * device pixel per CSS pixel, frames display a CSS-resolution downscale
 * generated here once per screenshot and cached as an object URL.
 *
 * Generation is best-effort: environments without OffscreenCanvas (server
 * rendering, test realms) simply keep the native bitmap.
 */
export declare function subscribeScreenshotBitmaps(listener: () => void): () => void;
/**
 * The CSS-resolution URL for a screenshot, or null while it generates (or
 * when it cannot be generated) — callers fall back to the native bitmap.
 * `width`/`height` are the frame's CSS dimensions.
 */
export declare function getDownscaledScreenshotUrl(key: string, dataUrl: string, width: number, height: number): string | null;
/** Test seam: forget cached and failed entries (object URLs are revoked). */
export declare function __resetScreenshotBitmapsForTest(): void;