entryText
How a history entry's command column holds what made it: the label of the command (update lib.f), then, after
a line break, the message it was given (-m), if any. One column, so the message goes wherever the entry does (a
push, a pull, a migration), with any tcm; it's in no hash, so it can change without changing history.
export const entryText = (command: string, message?: string) => message ? `${command}\n${message}` : command