/**
 * `HttpClient` — the optional cached-read path.
 *
 * When the host advertised an `httpEndpoint` at handshake, read-only,
 * `open`-gated capabilities route here instead of over the bridge: a plain
 * `POST` the host's Next.js backend can cache (`unstable_cache` / CDN), shared
 * across every mini-app and user.
 *
 * Wire contract (uniform across all capabilities — see `transport.ts`):
 * - `call`      → `POST {endpoint}/{method}` with body `{ capability, args }`,
 *                 response is the capability's JSON return value.
 * - `subscribe` → `EventSource` on
 *                 `GET {endpoint}/subscribe?capability=…&args=…`, one JSON
 *                 frame per event.
 *
 * NOTE for APNA-RD-HOST-008: the host's `/api/nostr/query` + `/api/nostr/subscribe`
 * routes (built in HOST-005/006) currently take `{ filters, relays?, revalidate? }`
 * / `?filters=&relays=`. They must be aligned to this uniform
 * `{ capability, args }` shape so HTTP and bridge are interchangeable transports
 * for the same `(capability, args)` call. Those routes are not wired to anything
 * yet, so the change is safe.
 */
/** Minimal `EventSource` shape — injectable for tests / non-browser runtimes. */
export interface EventSourceLike {
    onmessage: ((event: {
        data: string;
    }) => void) | null;
    onerror: ((event: unknown) => void) | null;
    close(): void;
}
export declare type EventSourceCtor = (url: string) => EventSourceLike;
export interface HttpClientOptions {
    /** Base URL the host advertised, e.g. `https://host/api/nostr`. */
    endpoint: string;
    /** In-flight promise dedup TTL in ms. Default 10000. */
    dedupTtlMs?: number;
    /** Injectable `fetch` (defaults to the global). */
    fetchImpl?: typeof fetch;
    /** Injectable `EventSource` constructor (defaults to the global). */
    eventSourceCtor?: EventSourceCtor;
}
export declare class HttpClient {
    private readonly endpoint;
    private readonly dedupTtlMs;
    private readonly fetchImpl;
    private readonly eventSourceCtor?;
    private readonly inflight;
    constructor(options: HttpClientOptions);
    /** POST a read-only capability call; identical in-flight calls are de-duped. */
    call(capability: string, args?: unknown[]): Promise<unknown>;
    /** Open an SSE stream for a read-only capability. Returns an unsubscribe fn. */
    subscribe(capability: string, args: unknown[], onEvent: (data: unknown) => void): () => void;
}