/** * usage.ts — Token usage: shapes, accumulator operators, session-stats readers.
 */
/**
 * Lifetime usage components, accumulated via `message_end` events. Survives
 * compaction. cacheRead is excluded because each turn's cacheRead is
 * the cumulative cached prefix re-read on that one call.
 */
export interface LifetimeUsage {
    input: number;
    output: number;
    cacheWrite: number;
}
/** Sum of lifetime usage components, or 0 if undefined. */
export declare function getLifetimeTotal(u?: LifetimeUsage): number;
/** Add a usage delta into a target accumulator (mutates target). */
export declare function addUsage(into: LifetimeUsage, delta: LifetimeUsage): void;
/** Minimal shape we read from upstream `getSessionStats()`. */
export interface SessionStatsLike {
    tokens: {
        input: number;
        output: number;
        cacheWrite: number;
    };
    contextUsage?: {
        percent: number | null;
    };
}
export interface SessionLike {
    getSessionStats(): SessionStatsLike;
}
/**
 * Session-scoped token count: input + output + cacheWrite as reported by
 * upstream `getSessionStats().tokens` for the *current* session window.
 *
 * RESETS at compaction. For a lifetime total, use `getLifetimeTotal`.
 */
export declare function getSessionTokens(session?: SessionLike): number;
/**
 * Context-window utilization (0–100), or null when unavailable.
 */
export declare function getSessionContextPercent(session?: SessionLike): number | null;