/**
 * Background NEXUS reindex after a merge into the base branch (T14010).
 *
 * The CLEO `post-merge` hook starts nothing unless the repository's git config
 * carries the {@link REINDEX_ON_MERGE_GIT_KEY} marker and HEAD is on the base
 * branch; both are checked in shell, so a disabled project pays no process
 * start on a merge or pull. `cleo nexus reindex-on-merge --enable` sets that
 * marker together with `nexus.reindexOnMerge.enabled`.
 *
 * When it runs, it is the lowest-priority heavy work on the machine: it never
 * joins the `cleo run` FIFO queue. It tries admission without waiting, only
 * when nothing is queued, and backs off between tries until its timeout
 * (default 300s), then records `deferred`. One runs at a time per project (a
 * lock file), and only real outcomes (ran, deferred, failed) are written to
 * `.cleo/nexus-reindex-on-merge.json` for `cleo nexus status`.
 *
 * Code placed in `packages/core/` per Package-Boundary Check — verified against AGENTS.md.
 *
 * @module nexus/reindex-on-merge
 * @task T14010
 */
/** File under `.cleo/` holding the last real outcome (ran, deferred, failed). */
export declare const REINDEX_ON_MERGE_OUTCOME_FILE = "nexus-reindex-on-merge.json";
/** Lock file under `.cleo/`; holds the pid of the running reindex. */
export declare const REINDEX_ON_MERGE_LOCK_FILE = "nexus-reindex.lock";
/** Git config key the `post-merge` hook checks before starting anything. */
export declare const REINDEX_ON_MERGE_GIT_KEY = "cleo.nexusReindexOnMerge";
/** Default seconds to keep trying for admission before recording `deferred`. */
export declare const DEFAULT_REINDEX_TIMEOUT_SECONDS = 300;
/** What a reindex-on-merge did. */
export interface ReindexOnMergeOutcome {
    /** `ran` (index refreshed), `skipped` (not recorded), `deferred` (machine busy) or `failed`. */
    outcome: 'ran' | 'skipped' | 'deferred' | 'failed';
    /** Why. */
    reason: string;
    /** When it finished (ISO 8601). */
    at: string;
    /** Wall-clock milliseconds. */
    durationMs: number;
}
/** Result of one admission attempt. */
export interface ReindexRunResult {
    /** Exit code of `cleo run`, or `null` when it could not start. */
    exitCode: number | null;
    /** Tail of its stderr, for the recorded reason. */
    stderr: string;
}
/** One admission attempt of `cleo nexus analyze`; replaceable in tests. */
export type ReindexRunner = (projectRoot: string) => ReindexRunResult;
/** Seams for tests: the attempt, the clock, the wait and the queue probe. */
export interface ReindexOnMergeDeps {
    /** One admission attempt (no `--wait`). */
    runner?: ReindexRunner;
    /** Clock in milliseconds. */
    now?: () => number;
    /** Wait between attempts. */
    sleep?: (ms: number) => Promise<void>;
    /** Whether any run is waiting in the `cleo run` queue. */
    queueBusy?: () => boolean;
}
/**
 * Turn reindex-on-merge on or off: `nexus.reindexOnMerge.enabled` and the git
 * config marker the `post-merge` hook checks, together.
 *
 * @param projectRoot - Project to configure.
 * @param enabled - The new setting.
 * @example
 * ```ts
 * await setReindexOnMerge(root, true);
 * ```
 */
export declare function setReindexOnMerge(projectRoot: string, enabled: boolean): Promise<void>;
/**
 * Reindex after a merge, when enabled, on the base branch, alone and admitted
 * at the lowest priority. Skips are returned, never recorded, so `nexus status`
 * keeps the last real outcome.
 *
 * @param projectRoot - Project whose index is refreshed.
 * @param deps - Test seams (attempt, clock, sleep, queue probe).
 * @returns The outcome.
 * @example
 * ```ts
 * const { outcome, reason } = await runReindexOnMerge(root);
 * ```
 */
export declare function runReindexOnMerge(projectRoot: string, deps?: ReindexOnMergeDeps): Promise<ReindexOnMergeOutcome>;
/**
 * The last recorded reindex-on-merge outcome, for `cleo nexus status`.
 *
 * @param projectRoot - Project to read.
 * @returns The outcome, or `null` when none was recorded or it is unreadable.
 */
export declare function readReindexOnMergeOutcome(projectRoot: string): ReindexOnMergeOutcome | null;
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