The throw site was passing (code, message) to a constructor whose
signature is (message, code), so exception.message ended up as the
literal string "BUILDER_INTERNAL_SERVER_ERROR" and the real
error.message was stored in exception.code where nothing reads it.
Swapping the two args puts the real error message back into
exception.message, which is the field Yoga's error handler copies into
the GraphQL response's top-level message — and that's the field the CLI
prints.
