wwiroundtrip pins the @packed re-emit through a real -I tree on both
driver stages (importer-side layout exit 91), strengthened with the
`struct @packed {` needle in the retained sepwork pk2.wwi (a
single-file two-package form emits no .wwi, so the tree is
irreducible). identityreject pins the stage asymmetry as a DIVERGE
row: cstage rejects with "not assignable" (packed is type identity,
harec types.c:621), wwstage builds+runs through the documented
#224/#10 nominal-lossy leniency; a wwstage tighten fails the row and
demands graduation to a //ww:error fixture. The 15 layout/runtime
value rows are fixture-shaped and move to the declarative corpus per
the residual audit port split.
