export interface TimelineDurationMessage {  id: string;  role: "user" | "assistant" | "system";  createdAt: string;  completedAt?: string | undefined;} export function computeMessageDurationStart(  messages: ReadonlyArray<TimelineDurationMessage>,): Map<string, string> {  const result = new Map<string, string>();  let lastBoundary: string | null = null;   for (const message of messages) {    if (message.role === "user") {      lastBoundary = message.createdAt;    }    result.set(message.id, lastBoundary ?? message.createdAt);    if (message.role === "assistant" && message.completedAt) {      lastBoundary = message.completedAt;    }  }   return result;} export function normalizeCompactToolLabel(value: string): string {  return value.replace(/\s+(?:complete|completed)\s*$/i, "").trim();}