/**
 * Where a page opens when no conversation is chosen (a first load, a new chapter, a remembered one that is gone):
 * the main agent's conversation, once the shared state and the main agents are known; 'create' when the main agent has no
 * conversation yet, as on a fresh preview. The root is only its history.
 */
export const landing = (
  loaded: boolean,
  chosen: unknown,
  mainAgent: Readonly<Record<string, number>> | null | undefined,
): number | 'create' | undefined => {
  if (!loaded || chosen !== undefined || mainAgent === undefined) return undefined
  return mainAgent?.['$main-agent'] ?? 'create'
}