/**
 * Serve a static file with production-grade cache headers:
 *   - Strong ETag (sha256, first 16 hex chars) computed once per
 *     `(path, mtime)` and cached in-process.
 *   - `Last-Modified` from the file's mtime.
 *   - 304 Not Modified when `If-None-Match` matches OR
 *     `If-Modified-Since` is at-or-after mtime (and ETag didn't mismatch).
 *   - `Cache-Control: public, max-age=31536000, immutable` for paths
 *     that look fingerprinted (e.g. `/_assets/foo.abc12345.js`).
 *   - `Cache-Control: public, max-age=300, must-revalidate` for
 *     everything else.
 *
 * Returns a `404` if the file doesn't exist. Other read errors propagate.
 *
 * @example
 * ```ts
 * import { serveFile } from '@stacksjs/storage'
 * import { resolve } from 'node:path'
 *
 * route.get('/assets/:path', async (req) => {
 *   const url = new URL(req.url)
 *   // url.pathname is e.g. /assets/app.abc12345.js
 *   const filePath = resolve('./public', url.pathname.replace(/^\//, ''))
 *   return serveFile(req, filePath)
 * })
 * ```
 */
export declare function serveFile(req: Request, filePath: string, options?: ServeFileOptions): Promise<Response>;
/**
 * Optional knobs for {@link serveFile}.
 */
export declare interface ServeFileOptions {
  contentType?: string
  cacheControl?: string
  defaultMaxAge?: number
  etag?: boolean
}