import type { AgentEnvironmentEvent } from "@tangle-network/agent-interface/environment-provider";
/**
 * Attaches an execution's running usage to the step frames of its stream.
 *
 * Sandbox reports an execution's usage on its terminal `result` and `done`
 * frames. Before those frames, the only usage on the stream is the OpenCode
 * harness's own `step_finish` event, which the sidecar forwards as a `raw`
 * frame with that step's token counts. No other harness the sidecar runs
 * forwards usage before the terminal frames, so their streams stay unchanged.
 */
export interface StepUsageFold {
    /**
     * The event, carrying the execution's cumulative usage when it reports a
     * step not yet counted. Every other event is returned unchanged.
     */
    observe(event: AgentEnvironmentEvent): AgentEnvironmentEvent;
}
/**
 * Create the fold for one stream that starts at its execution's first frame.
 *
 * A cumulative total counts every step before it, so a stream that resumes
 * after a cursor, or joins at a live tail, must not use this fold.
 *
 * The terminal receipt stays authoritative. Its usage is never replaced, and
 * the step frames are never rewritten to agree with it. A receipt below the
 * streamed total is therefore delivered as reported, and a consumer that folds
 * cumulative usage sees the total fall instead of a silently lowered total.
 */
export declare function createStepUsageFold(): StepUsageFold;