/**
 * Per-turn rolling token-usage accumulator for `$eve.*` observability
 * tags. Lives on `session.state` so the totals survive workflow step
 * boundaries the way the rest of the harness state does.
 *
 * The harness runs each turn as a sequence of `"use step"` invocations
 * (one per tool-loop iteration). Each step knows its own
 * `result.usage`, but the dashboard cares about totals **per turn**.
 * The workflow runtime's attribute store is "last write wins" per key,
 * so the simplest cumulative pattern is: read the previous total from
 * `session.state`, add the new step's usage, write the running total
 * back. The most recent emit then carries the final per-turn total.
 *
 * `turnId` keys the state so a fresh turn starts at zero without
 * relying on a separate "reset" code path — when the harness moves to
 * a new turn, the stale totals are discarded automatically.
 */
import type { HarnessSession, SessionStateMap } from "#harness/types.js";
/**
 * Rolling token usage for the in-flight turn.
 *
 * `turnId` is the in-flight turn's stable id; when the harness step
 * runs in a different turn (or with the empty-string between-turns
 * sentinel), totals are reset.
 */
export interface TurnUsageState {
    readonly cacheReadTokens: number;
    readonly inputTokens: number;
    readonly outputTokens: number;
    readonly turnId: string;
}
/** Reads the stored per-turn token state, or `undefined` when absent. */
export declare function getTurnUsageState(state: SessionStateMap | undefined): TurnUsageState | undefined;
/** Writes per-turn token state onto a new copy of the session. */
export declare function setTurnUsageState(session: HarnessSession, next: TurnUsageState): HarnessSession;
/**
 * Folds one step's `usage` into the running per-turn totals. When
 * `turnId` differs from the stored state (e.g. a new turn just
 * started), the previous totals are discarded — fresh turns start at
 * zero without an explicit reset path.
 */
export declare function accumulateTurnUsage(input: {
    readonly previous: TurnUsageState | undefined;
    readonly turnId: string;
    readonly usage: {
        readonly cachedInputTokens?: number;
        readonly inputTokens?: number;
        readonly outputTokens?: number;
    };
}): TurnUsageState;
