/**
 * TTS adapter factory with type guards
 *
 * Uses discriminated unions and lazy loading following SDK patterns.
 */
import type { BrowserSynthesisTTSOptions, TTSAdapter } from './types.js';
/**
 * Options for getting a TTS adapter
 */
export type GetTTSOptions = (BrowserSynthesisTTSOptions & {
    type?: 'browser-synthesis';
}) | {
    type: 'transformers';
};
/**
 * Create a TTS adapter
 *
 * Uses lazy loading to only import the requested adapter.
 *
 * @example
 * ```ts
 * // Browser Speech Synthesis (default)
 * const tts = await getTTS();
 *
 * // Explicit Browser Synthesis
 * const tts = await getTTS({ type: 'browser-synthesis' });
 *
 * // With custom defaults
 * const tts = await getTTS({ defaultRate: 1.2, defaultVoice: 'Google US English' });
 * ```
 */
export declare function getTTS(options?: GetTTSOptions): Promise<TTSAdapter>;
/**
 * Auto-detect and create the best available TTS adapter
 *
 * Selection priority:
 * 1. Browser Speech Synthesis (no download, instant)
 * 2. Transformers.js TTS (requires model download)
 *
 * @throws {Error} If no TTS adapter is available
 *
 * @example
 * ```ts
 * const tts = await getTTSAuto();
 * console.log(`Using ${tts.type} adapter`);
 * ```
 */
export declare function getTTSAuto(options?: Partial<Omit<GetTTSOptions, 'type'>>): Promise<TTSAdapter>;
/**
 * Check if a specific TTS backend is available
 */
export declare function isTTSAvailable(type: 'browser-synthesis' | 'transformers'): boolean;
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