/**
 * Observable write-queue.
 *
 * Tracks outstanding in-flight *logical* writes (a full Collection.put /
 * delete, including ledger + cache + derivation + MV dispatch — not just
 * the adapter call). The hub holds one tracker per instance; it is
 * framework-agnostic (no Vue/React dependency). UI layers subscribe via
 * onChange(); the migration drain (Slice 2) quiesces via onFlush().
 */
/** Public, read-only view of the hub's write-queue. */
export interface WriteQueue {
    /** True while one or more writes are in flight (`depth > 0`). */
    readonly pending: boolean;
    /** Count of outstanding write operations. */
    readonly depth: number;
    /**
     * Subscribe to depth changes (fires on every begin and settle).
     * Returns an unsubscribe function. Intended for reactive wrappers
     * (e.g. `@noy-db/in-vue` turns this into a `ref`).
     */
    onChange(handler: () => void): () => void;
    /**
     * Resolves once `depth` reaches 0. If a write settled with an error
     * while this flush was waiting, the returned promise REJECTS with that
     * error instead — so a drain caller surfaces the failure rather than
     * hanging. Resolves immediately when already idle and error-free.
     */
    onFlush(): Promise<void>;
}
export declare class WriteQueueTracker implements WriteQueue {
    #private;
    get pending(): boolean;
    get depth(): number;
    /** Mark one write as started. */
    begin(): void;
    /** Mark one write as finished. Pass the error if it failed. */
    settle(error?: Error): void;
    onChange(handler: () => void): () => void;
    onFlush(): Promise<void>;
    /**
     * Run `fn` as a tracked write: depth++ on entry, depth-- on settle
     * (success or failure). The fn's resolved value is returned; a thrown
     * error is re-thrown after the queue is decremented.
     */
    track<R>(fn: () => Promise<R>): Promise<R>;
}