summary-2 is generation 2
  summary-1 -> summary-2 (derived_from)
  user-3 -> summary-2 (derived_from)
  assistant-3 -> summary-2 (derived_from)
  user-4 -> summary-2 (derived_from)
  assistant-4 -> summary-2 (derived_from)
  user-1 -> summary-1 (derived_from)
  assistant-1 -> summary-1 (derived_from)
  user-2 -> summary-1 (derived_from)
  assistant-2 -> summary-1 (derived_from)
