/**
 * Who runs background sync on this machine, decided again on every tick.
 *
 * The watch service owns continuous sync while it runs, and the MCP process
 * stays a light tool server. When the service is not running, the MCP process
 * syncs. The MCP process used to ask this question once, at startup, and keep
 * the answer: on 2026-09-16 the service stopped, every MCP daemon that had
 * started while it ran kept standing by, and nothing synced for eight days.
 *
 * The answer can change in both directions, so it is asked on every interval:
 * the MCP process takes over when the service goes away and stands by again
 * when it comes back.
 *
 * Two writers never run at once. Every writer — the service, and each MCP
 * process — goes through `syncIncremental()`, which takes one O_EXCL lock and
 * skips its tick when another writer holds it. A tick this process already
 * started when the service came back finishes under that lock, and the service
 * waits for it.
 */
export type SyncScope = 'full' | 'changed';
export type SyncOwner = 'service' | 'mcp';
export interface SyncSupervisorOpts {
    /** Is the watch service running right now? A throw counts as "no". */
    serviceRunning: () => boolean;
    /** One sync pass. Errors are the caller's to log; a rejection is ignored here. */
    tick: (scope: SyncScope) => Promise<void>;
    /** Time between checks, and between sync passes while this process owns sync. */
    intervalMs: number;
    /** Time before the first check, so startup finishes before any sync work. */
    firstCheckMs: number;
    /** Called once, the first time this process takes over sync. */
    onFirstTakeover?: () => void;
    log?: (msg: string) => void;
}
export interface SyncSupervisor {
    /** Run one check now (the timers call this too). */
    check(): Promise<void>;
    /** Who owned sync at the last check; null before the first one. */
    owner(): SyncOwner | null;
    stop(): void;
}
export declare function createSyncSupervisor(opts: SyncSupervisorOpts): SyncSupervisor;
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