export function previewOnR2FromEnv(value: unknown): boolean;
export const PREVIEW_R2_READY_PATH: string;
export const PREVIEW_R2_READY_PROBE_LABEL: string;
export function makePreviewR2Ready(opts?: {
  previewHostSuffix?: string;
  fetchImpl?: typeof fetch;
  timeoutMs?: number;
}): () => Promise<boolean>;