import type { EmailDriver } from "../types.mjs";
/** Circuit-breaker states:
*   - `closed` — requests pass through
*   - `open` — requests short-circuit with a CANCELLED error
*   - `half-open` — a probe request is allowed; success closes, failure re-opens */
export type CircuitState = "closed" | "open" | "half-open";
export interface CircuitBreakerOptions {
	/** Consecutive failures that trip the breaker. Default: 5. */
	threshold?: number;
	/** How long to stay `open` before transitioning to `half-open`. Default: 30s. */
	cooldownMs?: number;
	/** Called on state transitions — useful for telemetry. */
	onStateChange?: (state: CircuitState) => void;
	/** Injected for tests. */
	now?: () => number;
}
/** Wrap a driver in a circuit breaker. Prevents cascading failures when a
*  provider is down by short-circuiting after `threshold` consecutive
*  errors. */
export declare function withCircuitBreaker(driver: EmailDriver, options?: CircuitBreakerOptions): EmailDriver;