/**
 * Darwin — Metrics Sink (v0.14.0)
 *
 * Every evolution decision as a typed event. The loop emits; you decide where
 * it goes — a JSONL file (built in, zero deps), Prometheus, OpenTelemetry
 * (see `examples/otel-bridge.ts`), or your own dashboard.
 *
 * Design rules, same as the rest of Darwin:
 *   - Zero hard deps. The sink is INJECTED (`DarwinLoopDeps.metrics`) or
 *     wired from the environment (`DARWIN_METRICS_JSONL=path`).
 *   - Fire-and-forget. A throwing/rejecting sink must never break the
 *     evolution loop — {@link emitMetric} swallows sink errors by contract.
 *   - Events are facts, not aggregates. Counters/histograms are the
 *     consumer's job; Darwin reports what happened, with enough payload to
 *     build any aggregate downstream.
 */
export type DarwinMetricEventType = 'run_recorded' | 'rollback' | 'ab_test_started' | 'ab_test_completed' | 'ab_test_timeout' | 'evolution_skipped';
export interface DarwinMetricEvent {
    /** What happened. */
    type: DarwinMetricEventType;
    /** Which agent it happened to. */
    agent: string;
    /** ISO timestamp, stamped at emit time. */
    at: string;
    /**
     * Event payload — intentionally loose. Stable keys per type (see the emit
     * sites in `evolution/loop.ts`): scores, versions, winner, failures, reason.
     */
    data: Record<string, unknown>;
}
export interface MetricsSink {
    /** Receive one event. May be sync or async; errors are swallowed by {@link emitMetric}. */
    emit(event: DarwinMetricEvent): void | Promise<void>;
}
/**
 * Emit `event` on `sink` without ever throwing — sync throws are caught,
 * async rejections attached. The evolution loop calls THIS, never
 * `sink.emit` directly, so a broken sink can not fail a run or an A/B
 * decision. No sink → no-op.
 */
export declare function emitMetric(sink: MetricsSink | undefined, type: DarwinMetricEventType, agent: string, data?: Record<string, unknown>): void;
/**
 * Append-only JSONL file sink — one event per line. The zero-dep default:
 * `tail -f` it, ship it with any log collector, or load it into a notebook.
 *
 * Writes are synchronous appends (events are small and rare — a handful per
 * agent run); the parent directory is created on first construction.
 */
export declare class JsonlMetricsSink implements MetricsSink {
    private readonly path;
    constructor(path: string);
    emit(event: DarwinMetricEvent): void;
}
/**
 * Build the sink the environment asks for, or `undefined` for none.
 * `DARWIN_METRICS_JSONL=<path>` → {@link JsonlMetricsSink} at that path.
 * Invalid paths fail loudly HERE (at wiring time), not silently per event.
 */
export declare function metricsSinkFromEnv(env?: NodeJS.ProcessEnv): MetricsSink | undefined;
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