/**
 * `ExtensionChannel` — the channel for the host-extension topology, where the
 * mini-app IS the top-level page and the host is a browser extension.
 *
 * The mini-app and a content-script relay share the page's `window`, so a
 * plain `ApnaMessage` posted to `window` can't tell "outbound to host" from
 * "inbound from host". This channel wraps every message in a tiny
 * direction-tagged `RelayEnvelope`:
 *
 *   SDK  --{ __apnaRelay: 'to-host', message }-->  content-script relay  -->  extension background
 *   SDK  <--{ __apnaRelay: 'to-app',  message }--  content-script relay  <--  extension background
 *
 * No host-extension exists yet, so this is lightly exercised (a mock relay in
 * unit tests) — but it implements the exact same `Channel` interface as
 * `IframeChannel`, so the protocol/bridge layers run over it unchanged.
 */
import { ApnaMessage } from '../protocol';
import { Channel } from './index';
/** Direction tags the SDK and the content-script relay agree on. */
export declare const RELAY_TO_HOST: "apna-relay:to-host";
export declare const RELAY_TO_APP: "apna-relay:to-app";
export interface ExtensionChannelOptions {
    /** Window to post to / listen on. Default: `window`. */
    window?: Window;
    /** Expected origin for validation. Default `'*'`. */
    targetOrigin?: string;
}
export declare class ExtensionChannel implements Channel {
    private readonly win;
    private readonly targetOrigin;
    private readonly handlers;
    private listening;
    private disposed;
    constructor(options?: ExtensionChannelOptions);
    send(message: ApnaMessage): void;
    onMessage(handler: (message: ApnaMessage) => void): () => void;
    /**
     * Resolves immediately — the content-script relay is injected at
     * `document_start`, so it is present before the mini-app's SDK runs. Real
     * protocol readiness is established by the handshake at the bridge layer.
     */
    ready(): Promise<void>;
    dispose(): void;
    private readonly onWindowMessage;
    private ensureListening;
    private stopListening;
}