/**
 * Nexus Connect — Client-side $socket() rune.
 *
 * Connects to /_nexus/connect/:topic via SSE and returns a reactive
 * state object whose .value updates in real time whenever the server publishes.
 *
 * Usage in a .nx island:
 *   <script>
 *   import { $socket } from '@nexus_js/connect/client';
 *
 *   const captures = $socket('global-captures', { default: { count: 0 } });
 *   // captures.value.count is always up-to-date
 *   </script>
 *   <p>Global captures: {captures.value.count}</p>
 */
export interface SocketState<T> {
    /** Current value — reactive in island components */
    readonly value: T;
    /** Register a callback that fires on every update */
    subscribe: (fn: (value: T, prev: T) => void) => () => void;
    /** Manually close the SSE connection */
    close: () => void;
    /** true while the SSE connection is establishing */
    readonly connecting: boolean;
    /** true if the connection is live */
    readonly connected: boolean;
}
export interface SocketOptions<T> {
    default: T;
    /** Optional transform applied to the raw JSON payload */
    transform?: (raw: unknown) => T;
    /** Called on SSE connection error */
    onError?: (err: Event) => void;
    /** Reconnect automatically on error (default: true) */
    reconnect?: boolean;
}
export declare function $socket<T>(topic: string, opts: SocketOptions<T>): SocketState<T>;
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