/**
 * Token Budget Enforcement (STORY-008)
 *
 * Provides fail-closed enforcement of per-model context window limits.
 * When total tokens exceed the model's hard limit, a structured error
 * is thrown instead of silently truncating.
 */
/**
 * Structured error thrown when token budget is exceeded.
 */
export declare class TokenBudgetExceededError extends Error {
    readonly code: "TOKEN_BUDGET_EXCEEDED";
    readonly budget: TokenBudget;
    constructor(budget: TokenBudget);
}
/**
 * Token budget breakdown by category.
 */
export interface TokenBudget {
    model: string;
    limitTokens: number;
    systemTokens: number;
    toolsTokens: number;
    historyTokens: number;
    totalTokens: number;
    withinBudget: boolean;
}
/**
 * Resolve the context window limit for a given model name.
 * Matches by prefix: "claude-sonnet-4-6" matches "claude" key.
 */
export declare function getModelLimit(model: string): number;
/**
 * Calculate token budget breakdown for a prompt.
 *
 * @param model - Model name (e.g., "claude-sonnet-4-6")
 * @param systemPrompt - System prompt text
 * @param toolsPrompt - Gateway tools prompt text
 * @param historyText - Conversation history text
 * @returns Token budget breakdown
 */
export declare function calculateBudget(model: string, systemPrompt: string, toolsPrompt?: string, historyText?: string): TokenBudget;
/**
 * Enforce token budget. Throws TokenBudgetExceededError if over limit.
 *
 * @throws {TokenBudgetExceededError} When total tokens exceed model limit
 */
export declare function enforceBudget(model: string, systemPrompt: string, toolsPrompt?: string, historyText?: string): TokenBudget;
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