/**
 * Metrics Interceptor
 *
 * Wraps a tool handler invocation to capture:
 *   - Wall-clock duration (using performance.now())
 *   - Input token estimate (from serialized args)
 *   - Output token estimate (from serialized result)
 *   - Error detection ({success: false} shape or thrown exceptions)
 *
 * Design rules:
 *   - NEVER throws — all interceptor errors are swallowed silently
 *   - ALWAYS returns the original handler result unchanged
 *   - Does NOT mutate the result (token injection happens separately in callTool)
 */
import type { MetricsAccumulator } from './metrics.js';
/** Handler function signature that the interceptor wraps */
export type ToolHandlerFn = (args: Record<string, unknown>) => Promise<unknown>;
/**
 * Wrap a tool handler with metrics collection.
 *
 * @param toolName  - Name of the tool being intercepted
 * @param handler   - The original tool handler function
 * @param accumulator - The MetricsAccumulator to record into
 * @returns A new async function with identical signature that records metrics
 */
export declare function wrapWithMetrics(toolName: string, handler: ToolHandlerFn, accumulator: MetricsAccumulator): ToolHandlerFn;
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