/**
 * KeyedMutex — serialize async work per key within one process.
 *
 * Used where a read-then-write decision must not interleave for the same
 * logical resource: intake's create-or-join per conversation key, and
 * included-time consumption per case during time-entry approval. Keys chain
 * promises, so concurrent callers for the same key run strictly in arrival
 * order while different keys stay fully parallel; entries clean up when the
 * last waiter finishes.
 *
 * Scope: in-process only. It covers the deployment shape these paths run in
 * (one app process owns intake interceptors / approval actions); multi-
 * replica deployments serialize at the app layer (sticky routing or a
 * DB-level claim), which composes above these seams.
 */
export declare class KeyedMutex {
    private readonly tails;
    /** Run `fn` exclusively for `key`, after every earlier holder of it. */
    run<T>(key: string, fn: () => Promise<T>): Promise<T>;
}
export default KeyedMutex;
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