/**
 * Relative-luminance cutoff between "dark enough for white text" and "light
 * enough for black text". WCAG's own crossover for #767676-class greys sits
 * near here; 0.179 is the value this assistant has shipped with.
 */
export declare const LUMINANCE_CUTOFF = 0.179;
/** Returned for anything unparseable, the safe default on a light product. */
export declare const FALLBACK_TEXT = "#000000";
/**
 * Black or white, whichever stays readable on `color`.
 *
 * The Style step offers one swatch per surface and `#585858` is a preset, so
 * without this a dark fill lands black text on near-black.
 *
 * Accepts three- and six-digit hex, with or without `#`. Falling back to black
 * on OTHER notations is deliberate: the built-in default is an `rgba()` string
 * that should keep the original black, and the dashboard picker only ever
 * emits hex.
 *
 * Shorthand was added 2026-08-29. Before it, `#000` failed to parse and fell
 * back to black, black text on a black launcher, invisible. The dashboard
 * never emits shorthand, but the config is writable by API and by
 * `assistant.sh update`, so an operator could always reach it.
 */
export declare function readableTextOn(color: string): string;