The set notation above is the human rendering of canonical singleton/range
domains. Alignment values are exponents: `[0, 63]` admits byte alignments
`2^0` through `2^63`. Both classes remain inside one physical
capability alternative, so endpoint bindings, actor-contract admission, and
use-pattern references are not duplicated. Contiguous `vector<2xf64>` is
rejected because element width 64 is absent even though its total payload also
has 128 bits.