/**
 * A per-project, single-flight pid lock for NEXUS background work (T14010,
 * T14014): the reindex after a merge and the inline refresh each run at most
 * once at a time per project.
 *
 * The pid is written to a private file that is then hard-linked into place, so
 * a reader never sees an empty lock. A dead holder is cleared by renaming the
 * lock to a unique name and checking the renamed file still holds that dead
 * pid, so two clearers cannot both win: only one rename succeeds, and a
 * clearer that moved a live lock by mistake puts it back. An empty or
 * unparseable lock younger than {@link PID_LOCK_WRITE_GRACE_MS} counts as a
 * holder still writing it. Release removes the lock only when it holds the
 * releaser's pid.
 *
 * Code placed in `packages/core/` per Package-Boundary Check — verified against AGENTS.md.
 *
 * @module nexus/pid-lock
 * @task T14014
 */
/** A lock file younger than this with no readable pid is a holder still writing it. */
export declare const PID_LOCK_WRITE_GRACE_MS = 5000;
/** Test seams: the pid to take the lock as, and how liveness is judged. */
export interface PidLockOptions {
    /** Pid written to the lock. @defaultValue process.pid */
    pid?: number;
    /** Whether a pid is alive. @defaultValue a signal-0 probe */
    isAlive?: (pid: number) => boolean;
}
/**
 * Take a pid lock atomically.
 *
 * @param lockPath - The lock file.
 * @param options - Test seams (pid, liveness).
 * @returns `null` when taken, or the pid of the live holder (`0` when unknown).
 * @example
 * ```ts
 * const holder = takePidLock(join(cleoDir, 'nexus-reindex.lock'));
 * if (holder === null) try { work(); } finally { releasePidLock(lockPath); }
 * ```
 */
export declare function takePidLock(lockPath: string, options?: PidLockOptions): number | null;
/**
 * Release a pid lock taken by {@link takePidLock}: removed only when it still
 * holds this pid, so a lock someone else took over is left alone.
 *
 * @param lockPath - The lock file.
 * @param pid - The holder releasing it. @defaultValue process.pid
 */
export declare function releasePidLock(lockPath: string, pid?: number): void;
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