/**
 * Token Estimator
 *
 * Provides a heuristic for estimating token counts without requiring a heavy tokenizer
 * dependency. Varies the byte-to-token ratio based on the content type to improve
 * accuracy for structured data and code.
 *
 * Ratios (empirically derived against tiktoken for GPT-4):
 *   - Prose: ~4.0 bytes/token (standard English)
 *   - JSON:  ~2.8 bytes/token (high density of structural characters)
 *   - Code:  ~3.2 bytes/token (mixed density)
 *
 * Usage:
 *   estimateTokens(str, contentType?)   → number
 *   estimatePayloadTokens(payload)      → number (always 'json')
 *   injectTokenEstimate(payload)        → payload with _meta.tokenEstimate added
 */
export type ContentType = 'prose' | 'json' | 'code';
/**
 * Detect the content type of a string to apply the most accurate token heuristic.
 */
export declare function detectContentType(text: string): ContentType;
/**
 * Estimate the number of tokens in a string using a content-type-aware heuristic.
 * If contentType is not provided, it is auto-detected.
 */
export declare function estimateTokens(text: string, contentType?: ContentType): number;
/**
 * Estimate tokens for an arbitrary serializable value by serializing it
 * to JSON first. Uses the 'json' content type heuristic.
 */
export declare function estimatePayloadTokens(payload: unknown): number;
/**
 * Inject a `_meta.tokenEstimate` field into a tool response payload.
 * Operates on a shallow copy — never mutates the original object.
 *
 * If the payload is not a plain object, returns it unchanged.
 * If `_meta` already exists, merges `tokenEstimate` into it.
 *
 * @param payload - Tool handler response (any shape)
 * @returns Payload with `_meta.tokenEstimate` added
 */
export declare function injectTokenEstimate(payload: unknown): unknown;
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