/**
 * Generates a unique ID, optionally with a prefix.
 *
 * Inside Svelte components prefer `$props.id()` (Svelte 5) — it is
 * deterministic across SSR and the client, so it avoids hydration
 * mismatches. This helper exists for non-component code (tests, build
 * tools) and uses `crypto.randomUUID()` when available, falling back
 * to `Math.random()` only on legacy runtimes.
 *
 * @param prefix - An optional prefix for the ID.
 * @returns A unique string ID.
 */
export declare function id(prefix?: string): string;