/**
 * Estimates the USD cost of an LLM call using character-based token approximation.
 * Rule of thumb: ~4 characters per token. Actual costs may vary.
 * Use for guardrail enforcement, not billing.
 */
export declare function estimateCost(inputText: string, outputText: string, model?: string): number;
export declare function formatCost(usd: number): string;
