/**
 * The trail: every result a workflow produced so far, over its own clock.
 *
 * What a workflow reports besides its answer - the steps it took, what they
 * cost over the time the whole thing took, and the first step that failed -
 * used to be kept by each combinator in its own variables, with its own
 * `performance.now()` and its own sum. The pool records into a trail as it
 * plays turns, so a combinator reads the envelope instead of keeping one.
 */
import type { Result } from "./../result.ts";
import { type Usage } from "./../usage.ts";
/** The results a workflow produced, in order, and what they add up to. */
export declare class Trail {
    /** Every result recorded, in the order it was recorded. */
    readonly steps: Result[];
    private readonly startedAt;
    /** Records a result and hands it back, so a step is recorded where it is made. */
    record<T extends Result>(result: T): T;
    /**
     * Every step's usage summed, over the time since the trail was opened.
     *
     * The wall time is the trail's own clock, not a sum: a fan-out of three
     * branches took as long as its slowest branch, and `busyMs / wallMs` is the
     * parallelism it really achieved.
     */
    usage(): Usage;
    /** The first step that failed, if any. What a workflow's `error` usually is. */
    broken(): Result | undefined;
}
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