ShapeEmptiness

Why a shape read came back with no regions. Absent (None) when the read returned rows.

UnreadableOrAbsent is deliberately ONE arm for two situations — a caller who cannot read the
anchor and an anchor that does not exist must stay indistinguishable, or the envelope becomes an
existence oracle. It discloses neither the population nor the clock. The other three arms are
only ever reached by a caller who passed the anchor gate, for whom "this anchor exists" is not a
disclosure.