839_xmod_nominal_typeeqast.c -> r839_xmod_nominal_match (run-exit 42),
r839_xmod_a6_concrete (run), r839_xmod_incompat_concrete (error
'not assignable'), r839_xmod_distinct_alias (error 'ambiguous
without nominal layout').
r839_xmod_nominal_match enters DATABYTEID_DIVERGED: the carrier waived
byte-id for the pre-existing cross-module tagged-return spill
divergence; the DIVERGED row makes it loud-on-fix instead. The
typeeqast-layer discriminator itself stays with the lib byteid gate
(test/byteid/libbyteid_test.ww), as the carrier documented.