import type { Sql } from "postgres";
import { type KeyOp } from "../../common/backend.js";
import type { PostgresConfig } from "../types.js";
/**
 * Creates isLocked operation for PostgreSQL backend.
 *
 * **Implementation Pattern:**
 * - Read-only by default (no side effects)
 * - Optional cleanup when cleanupInIsLocked: true (fire-and-forget)
 * - Uses server time for liveness check
 * - Simple boolean return value
 *
 * Flow:
 * 1. Normalize and validate key
 * 2. Query lock by key
 * 3. Check liveness using server time
 * 4. Optionally cleanup expired locks (fire-and-forget, with safety guard)
 * 5. Return boolean result
 *
 * @param sql - postgres.js SQL instance
 * @param config - PostgreSQL backend configuration
 * @returns IsLocked operation function
 *
 * @see docs/specs/interface.md#islocked-operation-requirements - Normative requirements
 */
export declare function createIsLockedOperation(sql: Sql, config: PostgresConfig): (opts: KeyOp) => Promise<boolean>;