import { HostedSpeechEngine } from './hostedTtsSpeechEngine';
import { SpeechEngine } from './types';
export interface SpeechEngineConfig {
    /** Our proxy's URL. Empty/undefined keeps the device engine. */
    endpoint?: string | null;
    getHeaders?: () => Record<string, string>;
    fetchImpl?: typeof fetch;
}
/**
 * Point the assistant at a hosted TTS proxy.
 *
 * Called by the host shell's provider, exactly as `configureGeocoder` is. This
 * is the supported way to turn hosted speech on; the environment variable below
 * only ever works when this package is run directly (dev / standalone).
 *
 * ★ `getHeaders` is not optional in practice, only in the type. The proxy turns
 * text into audio the org is BILLED for, so an endpoint that accepts anonymous
 * POSTs is a metered API open to anyone who reads the bundle. The engine has
 * always supported per-request headers; until now nothing could reach that hook
 * from the host, which meant the only configuration this function could express
 * was an unauthenticated one. It is a function rather than a value because
 * access tokens expire and the engine outlives any one of them — reading a
 * token once at configure time would work until it rotated and then fail
 * exactly where it is hardest to notice, mid-reply.
 *
 * ★ Several callers may configure, and the LAST `getHeaders` given wins, without
 * rebuilding the engine. Only a change of ENDPOINT rebuilds it. A call that
 * repeats the endpoint without `getHeaders` keeps the existing source rather
 * than silently making every later request anonymous (and refused).
 */
export declare function configureSpeechEngine(options: {
    ttsEndpoint?: string | null;
    getHeaders?: () => Record<string, string>;
}): void;
/**
 * Read the rollout config.
 *
 * Order matters: explicit runtime configuration, then a global the host can set
 * before the bundle loads, and only then the build-time variable — which is
 * eliminated in the published package and therefore useful for local dev only.
 */
export declare function readSpeechEngineConfig(): SpeechEngineConfig;
/**
 * The engine to use, or the device engine when hosted TTS is not configured.
 *
 * Returns `null` for `hosted` when off, so callers can tell "hosted is not
 * configured" from "hosted is configured but cannot speak this language".
 */
export declare function createSpeechEngines(config?: SpeechEngineConfig): {
    device: SpeechEngine;
    hosted: HostedSpeechEngine | null;
};
export declare function getSpeechEngine(): SpeechEngine;
/**
 * Be told when `getSpeechEngine()` would return a different engine.
 *
 * ★★ Without this a panel mounted BEFORE the host configured hosted speech kept
 * the device engine it read at mount (BOFF-7283): `AssistantSpeechProvider`
 * read the engine as a default prop, so it only noticed the change if something
 * else happened to re-render it — and until then spoke with the device voice.
 * The provider subscribes through `useSyncExternalStore`.
 */
export declare function subscribeSpeechEngine(listener: () => void): () => void;
/**
 * Drop the singleton so the next call re-reads the config, and tell subscribers.
 *
 * ★ The notification is DEFERRED to a microtask. `configureSpeechEngine` is
 * called during render by the product providers, and a synchronous notify would
 * update another component while this one is rendering — which React rejects.
 * Coalesced, so a burst of resets notifies once.
 */
export declare function resetSpeechEngine(): void;
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