The space's root hash — one number over every statement's latest chain link, and nothing else. A public memory proves itself by being fully replayable; a private one proves itself by publishing a number that discloses nothing and that an altered record cannot reproduce.
response200 — the number, and how much it covers
no content leaves: the root is built from hashes, and nothing in it can be turned back into a statement
worth as much as the publishing — recorded somewhere this instance does not control, every later read becomes a check