import type { BudgetCaps, StopReason, UsageSnapshot } from "./types.js";
/**
 * Tracks per-session usage against `BudgetCaps`. Consumed by the runner's
 * step boundary: after every LLM step + tool batch, we record the usage and
 * ask `nextStopReason()` whether to terminate.
 *
 * Wall time is measured from `start()`. Cost is estimated using the existing
 * `estimateCostUsd` table; for unknown providers/models, cost defaults to 0
 * which means USD caps don't fire — caller is responsible for ensuring
 * provider/model are recognized when USD enforcement matters.
 */
export declare class BudgetTracker {
    private readonly caps;
    private readonly providerId;
    private readonly modelId;
    private inputTokens;
    private outputTokens;
    private toolCallCount;
    private externalUsd;
    private startedAt;
    /** Largest observed input-token count for any single step. Drives the projection. */
    private maxStepInputTokens;
    private maxStepOutputTokens;
    private stepCount;
    constructor(caps: BudgetCaps, providerId: string, modelId: string);
    start(): void;
    recordStepUsage(usage: {
        inputTokens?: number;
        outputTokens?: number;
    }): number;
    recordToolCalls(n: number): void;
    /**
     * Record a non-LLM external API cost (SerpAPI calls, AI-engine probes,
     * etc.) so the session budget accurately reflects total spend, not just
     * orchestrator-LLM tokens.
     */
    recordExternalCost(usd: number): void;
    estimatedUsd(): number;
    snapshot(): UsageSnapshot;
    /**
     * Returns the StopReason that fires now, or null when no cap is breached.
     * Order matters — earlier checks take priority when multiple caps exceed
     * simultaneously (most informative reason wins).
     */
    nextStopReason(): StopReason | null;
    /**
     * Pre-flight projection: would executing one more step at the worst-case
     * (max observed) per-step cost push us over the USD or input-token cap?
     * Used by `stopWhen` to refuse the next step before it overshoots, rather
     * than reactively after.
     *
     * Returns null until at least one step has completed — we have nothing
     * to project from before that.
     */
    projectedNextStopReason(): StopReason | null;
}
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