/**
 * Whether a `tool_done` event failed.
 *
 * Trace instrumentation and trace-to-eval promotion must share this rule.
 * Legacy events omit `isError` and encode failure by prefixing `result` with
 * `"Error"` or `"Error running "`. A boolean `isError` always wins, including
 * `false`, so a successful result that happens to start with those letters is
 * not inferred as a failure when the producer set the flag.
 */
export declare function isToolDoneFailure(event: {
    isError?: unknown;
    result?: unknown;
}): boolean;