/**
 * Audio-platform registry — enumerates all known MusicBackend implementations
 * and provides availability helpers.
 *
 * A backend is available iff:
 *   - every var in requiredEnv is set (non-empty) in env, AND
 *   - (!requiresVertex || at least one of GOOGLE_CLOUD_PROJECT / VERTEX_PROJECT
 *     / GCLOUD_PROJECT is set in env), AND
 *   - (!requiresGeminiKey || at least one of GEMINI_API_KEYS / GOOGLE_API_KEYS
 *     / GOOGLE_API_KEY is set in env)
 *
 * The Gemini-key gate (requiresGeminiKey) covers API-key Gemini products such
 * as the Lyria 3 music backend: they declare an empty requiredEnv (no single
 * fixed var) and resolve a key from the pool sources. Gating on the flag — not
 * the backend id — keeps the rule decoupled from backend identity.
 *
 * Vertex credential liveness (ADC token validity) is NOT checked here — that
 * would require a network call. The check is intentionally env-only so it is
 * synchronous, pure, and testable.
 */
import type { MusicBackend, SfxBackend, TtsBackend } from './types.js';
/** All registered music backends, in priority order. */
export declare const MUSIC_BACKENDS: MusicBackend[];
/**
 * All registered TTS backends, in priority order. `gemini-tts` stays first (the
 * documented default), with `elevenlabs-tts` as the Gemini-free alternative —
 * selected explicitly via `--backend elevenlabs-tts` (or auto-picked when it is
 * the only available backend).
 */
export declare const TTS_BACKENDS: TtsBackend[];
/**
 * Returns true if the backend's runtime prerequisites are satisfied in `env`.
 * Pure and synchronous — no network calls.
 */
export declare function isMusicBackendAvailable(b: MusicBackend, env?: NodeJS.ProcessEnv): boolean;
/**
 * Returns all music backends that are currently available in `env`.
 */
export declare function listAvailableMusicBackends(env?: NodeJS.ProcessEnv): MusicBackend[];
/**
 * Returns the MusicBackend with the given `id`, or throws if not found.
 * Does NOT check availability — the caller decides whether to gate on it.
 */
export declare function getMusicBackend(id: string): MusicBackend;
/**
 * Returns true if the TTS backend's runtime prerequisites are satisfied in
 * `env`. Pure and synchronous — no network calls.
 *
 * Backends that set `requiresGeminiKey` (e.g. gemini-tts) declare an empty
 * requiredEnv (an API-key product, not a fixed env-var product), so
 * availability additionally requires a Gemini key from the pool sources: at
 * least one of GEMINI_API_KEYS / GOOGLE_API_KEYS / GOOGLE_API_KEY must be set
 * and non-empty. Gating on the flag (not the backend id) keeps this rule
 * decoupled from backend identity and extensible to future TTS backends.
 */
export declare function isTtsBackendAvailable(b: TtsBackend, env?: NodeJS.ProcessEnv): boolean;
/**
 * Returns all TTS backends that are currently available in `env`.
 */
export declare function listAvailableTtsBackends(env?: NodeJS.ProcessEnv): TtsBackend[];
/**
 * Returns the TtsBackend with the given `id`, or throws if not found.
 * Does NOT check availability — the caller decides whether to gate on it.
 */
export declare function getTtsBackend(id: string): TtsBackend;
/** All registered SFX backends, in priority order. */
export declare const SFX_BACKENDS: SfxBackend[];
/**
 * Returns true if the SFX backend's runtime prerequisites are satisfied in
 * `env`. Pure and synchronous — no network calls.
 */
export declare function isSfxBackendAvailable(b: SfxBackend, env?: NodeJS.ProcessEnv): boolean;
/**
 * Returns all SFX backends that are currently available in `env`.
 */
export declare function listAvailableSfxBackends(env?: NodeJS.ProcessEnv): SfxBackend[];
/**
 * Returns the SfxBackend with the given `id`, or throws if not found.
 * Does NOT check availability — the caller decides whether to gate on it.
 */
export declare function getSfxBackend(id: string): SfxBackend;
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