/**
 * Share one in-flight promise per key: callers that ask again while a request
 * for the same key is still pending get that request instead of a new one.
 */
export function dedupeInFlight<T>(): (key: string, run: () => Promise<T>) => Promise<T> {
  const pending = new Map<string, Promise<T>>();
  return (key, run) => {
    const existing = pending.get(key);
    if (existing) return existing;
    const p = run().finally(() => pending.delete(key));
    pending.set(key, p);
    return p;
  };
}