import type { Pool } from "pg";
export declare const REFILL_INTERVAL_MS = 10000;
export interface HostBudget {
    capacity: number;
    refillPerInterval: number;
}
export declare const DEFAULT_HOST_BUDGET: Readonly<HostBudget>;
export interface HostBudgetOptions {
    pool: Pick<Pool, "connect">;
    hostClasses?: Readonly<Record<string, HostBudget>>;
    /** Test clock only. Production uses the DB clock sampled after acquiring the row lock. */
    now?: () => Date;
}
export declare function retryAfterDeadline(headers: Headers, now: number): number | undefined;
export declare class HostBudgets {
    private readonly options;
    constructor(options: HostBudgetOptions);
    private configuration;
    private locked;
    consume(host: string, hostClass: string): Promise<void>;
    /** Header hints can only tighten a shared budget; parking is monotone under concurrent responses. */
    observe(host: string, hostClass: string, status: number, headers: Headers): Promise<void>;
}