Multi-currency — It never guesses

Where no declared rate covers a pair, RowFold produces no number for it. It does not fall back to 1.0, and it does not reach for the newest rate lying around. The lines it could not convert are counted, named and reported next to the figure — “9 of 10 — 1 needs a JPY→USD rate” — rather than dropped, which would quietly total a subset and present it as the answer. A workspace that records several currencies but has declared no rates at all still reports its cross-currency lines as unconvertible. Going quiet there would be adding pounds to dollars, which is the exact failure this layer exists to prevent. The principle, and it is the same one behind units: a number that is wrong without being visibly wrong is worse than no number. Both features would rather refuse and say why.