After the frontend consolidated into one syntax package, the wcc backend
imports syntax and calls its exported fns — whose signatures reference
types that were unexported. Producing syntax's .wwi interface re-triggered
check_exported_type ("exported declaration references unexported type"):
the residual of BUG-A at the one surviving syntax->wcc boundary. Export
the 16 types that appear in syntax's wcc-facing public surface (directly
in an exported signature, or via a recursively-referenced exported struct
field): nkind, node, lex, tok, tkind, parser, scope, sym, skind, tinfo,
tykind, tfield, tparam, ttupleelem, tctx, tinfocacheent. The set is
minimal (unexporting any one re-breaks the producer) and complete; pos
stays internal. Pure source change — exporting a type emits no code, so
the bootstrap binaries are byte-identical (verified against a clean base
build); only syntax's .wwi gains the type decls.
Post-frontend-reorg residual (#74). syntax now sep-produces clean both
stages. The separate concern of wcc's currently-unqualified refs to
syntax symbols (#75) is a distinct follow-up. Gate 989_syntaxexport_run.
