/**
 * @jorvel/ssr — request-time ISR (Incremental Static Regeneration).
 *
 * Stale-while-revalidate for SSR HTML: serve a cached page instantly; when it's
 * older than `revalidateMs`, serve the stale copy AND re-render in the
 * background so the next request is fresh. Complements build-time
 * `revalidateStaticPages` and the `LruHtmlCache`.
 *
 * Bring any {@link HtmlCache} (in-memory default, or a Redis/KV-backed one for
 * multi-instance). Deduplicates concurrent background regenerations per key.
 */
import type { HtmlCache } from './html-cache.js';
export interface IsrRenderResult {
    html: string;
    status?: number;
    etag?: string;
}
export interface ServeIsrOptions {
    cache: HtmlCache;
    key: string;
    /** Produce a fresh page. Called on miss and (in the background) when stale. */
    render: () => Promise<IsrRenderResult> | IsrRenderResult;
    /** Serve cached HTML younger than this without regenerating (ms). */
    revalidateMs: number;
    /** Clock (testable). */
    now?: () => number;
}
export interface ServeIsrResult {
    html: string;
    status: number;
    etag: string;
    /** true when served from cache (fresh OR stale). */
    cached: boolean;
    /** true when served stale + a background revalidation was kicked off. */
    stale: boolean;
}
/**
 * Serve `key` with ISR semantics. Fresh → cache hit; stale → serve stale +
 * background regenerate; miss → render synchronously and cache.
 */
export declare function serveWithISR(opts: ServeIsrOptions): Promise<ServeIsrResult>;
/** Await any in-flight background regeneration for a key (tests / graceful shutdown). */
export declare function awaitIsrRevalidation(key: string): Promise<void>;
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