A widening sub-union cast (return/let `v: inner` into a union whose member
is the nested `inner`) skipped the nested widen arm and emitted tag=0 (a
2nd-variant value returned the wrong payload). cstage loud-stops #35;
wwstage now matches: cgwidentaggedstorebp louds on the subset cast, and
cgreturn routes genuine-widening tagged returns (rhs TY_TAGGED, ru1!=fu1)
through the widener choke-point so the same loud fires. Same-type returns
stay on the proven passthrough. Faithful inner-tag->outer-index remap
deferred. test/wcc/835 S1 row.
isassignable's untyped-int arm fell through *confident=false/return true,
silently accepting an untyped int into a union whose variant is itself a
nested (non-flattened) union; ww emitted tag=0 (wrong arm) where cstage
louds. Reject unless a direct variant is numeric-or-enum (N_TENUM accept
mirrors cstage type_isnum). Faithful flatten+rebox deferred (nominal
identity, post-CSP). test/wcc/835 (new) + Makefile.
