/**
 * CircuitBreaker — pure state-machine functions for the Nygard breaker
 * pattern.
 *
 * Refactored from a class-with-instance-state to PURE FUNCTIONS that
 * take a state record and return a new one. Reasons:
 *
 *   1. **No hidden runtime state.** Breaker state lives in scope where
 *      it's visible to commitLog, narrative, and rules — the footprintjs
 *      "everything in scope" principle. The closure used to be the
 *      source of truth and scope held only a projection; now scope IS
 *      the source of truth.
 *
 *   2. **Round-trippable across gate invocations.** Because state is a
 *      plain record, gate's outputMapper writes it back to agent scope;
 *      agent scope persists across the ReAct loop's many LLM-call gate
 *      invocations; gate's inputMapper reads it back in for the next
 *      call. Per-process persistence comes from the agent scope, not
 *      from a closure that hides between runs.
 *
 *   3. **Distributable later.** A future v2.12 `BreakerStateStore`
 *      adapter (Redis/DynamoDB) just needs to serialize/deserialize the
 *      state record. No class instances to reconstruct.
 *
 *   4. **Testable in isolation.** Pure functions; no instance setup.
 *
 * Pattern: Nygard *Release It!* — three states (CLOSED → OPEN →
 *          HALF-OPEN) with cooldown and probe-success thresholds.
 */
import type { CircuitBreakerConfig } from './types.js';
export type CircuitState = 'closed' | 'open' | 'half-open';
/** Plain serializable record holding one breaker's full state. */
export interface BreakerState {
    state: CircuitState;
    consecutiveFailures: number;
    consecutiveSuccesses: number;
    openedAt: number;
    lastErrorMessage?: string;
}
/**
 * Thrown by `assertAdmit()` when the breaker is OPEN and the cooldown
 * window has not elapsed. The reliability gate stage catches this,
 * classifies via `classifyError` → `'circuit-open'`, and lets the
 * post-decide rules route on it.
 */
export declare class CircuitOpenError extends Error {
    readonly code: "ERR_CIRCUIT_OPEN";
    readonly cause: unknown;
    readonly retryAfter: number;
    constructor(providerName: string, lastErrorMessage: string | undefined, retryAfter: number);
}
/** Initial state for a freshly-CLOSED breaker. */
export declare function initialBreakerState(): BreakerState;
/**
 * Decide whether to admit a call. Returns the (possibly-updated) state
 * AND whether to admit. If OPEN and cooldown elapsed, transitions to
 * HALF-OPEN and admits. Pure: caller must use the returned state.
 *
 * Usage in the gate stage:
 * ```ts
 * const { admitted, nextState } = admitCall(scope.breakerStates[name], config);
 * scope.breakerStates[name] = nextState;
 * if (!admitted) throw new CircuitOpenError(name, nextState.lastErrorMessage, ...);
 * ```
 */
export declare function admitCall(state: BreakerState, config: CircuitBreakerConfig | undefined): {
    admitted: boolean;
    nextState: BreakerState;
};
/** Record a successful call. Returns the (possibly-updated) state. */
export declare function recordSuccess(state: BreakerState, config: CircuitBreakerConfig | undefined): BreakerState;
/** Record a failed call. Returns the (possibly-updated) state. */
export declare function recordFailure(state: BreakerState, err: unknown, config: CircuitBreakerConfig | undefined): BreakerState;
/** Compute the next probe time given a state + config. */
export declare function nextProbeTime(state: BreakerState, config: CircuitBreakerConfig | undefined): number;