/**
 * AudioManager — handles all audio playback for the browser client.
 *
 * Public interface: unlock(), handleAudioEvent(), dispose().
 * Manages ambient loops and music tracks via the Web Audio API
 * (per-stream MediaElementAudioSourceNode -> GainNode graph) with
 * sample-accurate fade-in / fade-out / cross-fade. SFX uses a bare
 * HTMLAudioElement and is exempt from fades by design (ADR-169).
 *
 * If the browser cannot create an AudioContext, the manager falls
 * back to instant-gain mode: audio still plays via HTMLAudioElement,
 * fade ramps are skipped.
 *
 * Owner context: @sharpee/platform-browser
 */
export declare class AudioManager {
    private ambientChannels;
    private musicTrack;
    private outgoingStreams;
    private audioContext;
    private instantGainMode;
    private unlocked;
    private pendingEvents;
    /**
     * Unlock audio playback. Must be called from a user gesture handler
     * (keydown, click) so the browser allows AudioContext.resume() and
     * Audio.play(). Constructs the AudioContext lazily on first call.
     */
    unlock(): Promise<void>;
    /**
     * Handle an audio event from the engine's event pipeline.
     * Queues events until audio is unlocked by a user gesture.
     *
     * @param event - Object with `type` and `data` fields.
     */
    handleAudioEvent(event: {
        type: string;
        data: any;
    }): void;
    /**
     * Tear down all audio resources. Cuts audio without ramping —
     * dispose is the explicit teardown path. Safe to call before
     * unlock(): the AudioContext close is null-guarded.
     */
    dispose(): void;
    private playAmbient;
    private stopAmbient;
    private stopAllAmbient;
    private playMusic;
    private stopMusic;
    private playSfx;
    /**
     * Construct a new stream: HTMLAudioElement + (optionally) Web Audio
     * graph + fade-in ramp. Returns null only on truly unrecoverable
     * failure (no src). In all other cases returns an ActiveStream,
     * possibly in instant-gain mode (graph nodes null).
     */
    private startStream;
    /**
     * Begin a fade-out on `stream` and schedule its teardown after the
     * fade completes. The stream is moved into `outgoingStreams` until
     * teardown fires.
     */
    private startFadeOut;
    /**
     * Schedule a fade-in ramp from 0 to target on the gain node.
     * Anchors at 0 with setValueAtTime so the ramp has a defined start.
     */
    private scheduleFadeIn;
    /**
     * Tear down a stream's graph + element synchronously, no ramping.
     * Used by dispose() and at the tail of fade-out timers.
     */
    private teardownStreamInstant;
    /**
     * Validate a fade-duration value from event payload.
     * Returns the value in ms, or undefined if invalid (callers fall
     * back to defaults). Per ADR-169: negative, NaN, non-finite, and
     * Infinity are all invalid; 0 is honored (instant cut).
     */
    private validateFadeMs;
}
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