### Changed

- BUILDER.md's green ruled term now says which entry to read before it says
  what an entry means: a check's word at a head is its newest entry by start
  time, and a cancelled entry is not that word while the same check carries a
  non-cancelled one at that head (#276).
- A check whose every entry at the head is cancelled is unchanged — nothing
  survived to be its word, so it never reported and is not green — and the
  collapse mirrors `checks_state`'s carve-out rather than adding a class
  (#276).