A stand-in for a kept tcm build, for tests: `<root>/<where>`, recorded as `pnpm verify` records one (made from `head`, `hoursAgo`), whose tcm.js prints what it was asked as JSON (`says`, its arguments, the directory, and the TCM_CODEBASE and TCM_BRANCH it saw), exiting 1 if the first argument is `fail`. Its directory.
Builds are named known-good, previous, and (older ones) the history entry they were made from; each resolves to its tcm.js, as a path does, and a name that's none of them says what's kept.
The build a new known-good replaces is kept, named by the entry it was made from, and only the newest few are: one that doesn't say what it was made from goes.