what promise does ender make to the bugger queen

Ender promises to take the cocoon and "go from world to world" until he finds a time and place for her to awake in safety. He also decides to tell the buggers' story to the humans, so that they can forgive the buggers. Within a few weeks, basically channeling the queen's thoughts, he writes their history and notes that they forgave the humans for killing them. The hive-queen says that the two species are "tragic sisters" who killed one another, even though the queen would now welcome humans "as guestfriends." Ender signs the book as "Speaker for the Dead."