/**
 * Minimal FIFO counting semaphore for bounding concurrent runtime runs.
 *
 * Admission-control only: a caller acquires immediately before starting work
 * and releases when done. Callers waiting for a permit hold nothing, so a
 * queued follow-up (waiting in the live-session queue) never occupies a slot —
 * which is what keeps `maxConcurrentRuns` from deadlocking against the
 * per-conversation queue.
 */
export interface Semaphore {
    /**
     * Acquire a permit. If `signal` aborts while waiting for admission, the
     * returned promise rejects with {@link SemaphoreAcquireAbortedError} and the
     * waiter is dropped from the queue without ever consuming a permit.
     */
    acquire(signal?: AbortSignal): Promise<void>;
    release(): void;
    /** Permits currently held. */
    inUse(): number;
}
/** Thrown by {@link Semaphore.acquire} when the wait is aborted before admission. */
export declare class SemaphoreAcquireAbortedError extends Error {
    constructor();
}
export declare function createSemaphore(maxConcurrent: number): Semaphore;
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