/**
 * "Flash on update": a short, non-interactive outline over every Lit element
 * that just finished an update cycle, so re-render churn is visible on the
 * page itself rather than only in the Updates tab.
 *
 * Sibling of the inspector's hover outline, not a reuse of it — many elements
 * can flash in the same frame, and each box has its own fade. Same drawing
 * rules though: one `position: fixed` layer with `pointer-events: none` so the
 * page stays fully interactive underneath.
 *
 * Fed by the lifecycle layer's update hook (see `setUpdateHook` in
 * `lifecycle.ts`), which fires whether or not the timeline is recording. Rects
 * are measured once per animation frame for every element that updated in it,
 * so a tick that updates a hundred components costs one layout, not a hundred.
 *
 * Off by default; the panel turns it on through the settings override.
 */
import type { UpdateHook } from './lifecycle.js';
/**
 * Heat level for `count` updates of one element inside the ramp window.
 * Exported for the unit test; the thresholds are the whole behaviour.
 */
export declare const rampLevel: (count: number) => number;
/** Turn the overlay on or off; off also wipes whatever is mid-fade. */
export declare const setFlashEnabled: (on: boolean) => void;
/** Colour by update frequency instead of the flat colour. */
export declare const setFlashRamp: (on: boolean) => void;
/**
 * The lifecycle layer's update hook. Cheap on the hot path: one Map write and,
 * at most, one `requestAnimationFrame` per frame; all measuring happens in
 * the flush.
 */
export declare const flashUpdate: UpdateHook;
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