wording: store the error as unexpected<E> in the primary and void specs

The step-1 relaxation lets expected<T, E> and expected<void, E> take an
lvalue-reference E, but their ratified exposition stores the error as a
bare union member E unex, which is ill-formed for E& (same as-if defect
just fixed in [expected.ref]). Change both union members to unexpected<E>
and route error access through unex.error().

The edit is surgical: construct_at(addressof(unex), ...), reinit-expected,
swap(unex, rhs.unex), and the "direct-non-list-initializes unex with the
error" construction prose all operate correctly on unexpected<E> unchanged.
Only the four error() returns (-> unex.error()), the same-state assignment
lines (unex = rhs.unex; and unex = unexpected<E>(...e.error())), and the
primary swap's temporary (E tmp -> unexpected<E> tmp) change. unexpected<E>
assignment gives rebind for reference E and assign-through for object E,
which is exactly the intended semantics.

Left as a follow-up (equivalent, not incorrect): the swap noexcept
specification still tests is_nothrow_swappable_v<E>, which is
over-conservative for a reference E (the pointer swap is always noexcept).

Verified: build clean at 93 pages; stripped diff vs expected-base.tex
changes exactly the 16 intended lines (13 storage + 3 relaxation), no
churn; bad_expected_access and unexpected keep E unex (a reference class
member, not a union member, is legal).

Author: steve-downey

papers/expected-new.tex

@@ -612,7 +612,7 @@
     bool @\exposid{has_val}@;           // \expos
     union {
       remove_cv_t<T> @\exposid{val}@;   // \expos
-      E @\exposid{unex}@;               // \expos
+      unexpected<E> @\exposid{unex}@;   // \expos
     };
   };
 }
@@ -1062,7 +1062,7 @@
 @\exposid{reinit-expected}@(@\exposid{val}@, @\exposid{unex}@, *rhs)
 \end{codeblock}
 \item
-Otherwise, equivalent to \tcode{\exposid{unex} = rhs.error()}.
+Otherwise, equivalent to \tcode{\exposid{unex} = rhs.\exposid{unex}}.
 \end{itemize}
 Then, if no exception was thrown,
 equivalent to: \tcode{\exposid{has_val} = rhs.has_value(); return *this;}
@@ -1139,7 +1139,7 @@
 @\exposid{reinit-expected}@(@\exposid{val}@, @\exposid{unex}@, std::move(*rhs))
 \end{codeblock}
 \item
-Otherwise, equivalent to \tcode{\exposid{unex} = std::move(rhs.error())}.
+Otherwise, equivalent to \tcode{\exposid{unex} = std::move(rhs.\exposid{unex})}.
 \end{itemize}
 Then, if no exception was thrown,
 equivalent to: \tcode{has_val = rhs.has_value(); return *this;}
@@ -1247,7 +1247,7 @@
 \end{codeblock}
 \item
 Otherwise, equivalent to:
-\tcode{\exposid{unex} = std::forward<GF>(e.error());}
+\tcode{\exposid{unex} = unexpected<E>(std::forward<GF>(e.error()));}
 \end{itemize}
 
 \pnum
@@ -1349,7 +1349,7 @@
 \tcode{this->has_value()} is \tcode{true}, equivalent to:
 \begin{codeblock}
 if constexpr (is_nothrow_move_constructible_v<E>) {
-  E tmp(std::move(rhs.@\exposid{unex}@));
+  unexpected<E> tmp(std::move(rhs.@\exposid{unex}@));
   destroy_at(addressof(rhs.@\exposid{unex}@));
   try {
     construct_at(addressof(rhs.@\exposid{val}@), std::move(@\exposid{val}@));
@@ -1517,7 +1517,7 @@
 
 \pnum
 \returns
-\exposid{unex}.
+\tcode{\exposid{unex}.error()}.
 \end{itemdescr}
 
 \indexlibrarymember{error}{expected}%
@@ -1533,7 +1533,7 @@
 
 \pnum
 \returns
-\tcode{std::move(\exposid{unex})}.
+\tcode{std::move(\exposid{unex}).error()}.
 \end{itemdescr}
 
 \indexlibrarymember{value_or}{expected}%
@@ -2025,7 +2025,7 @@
 private:
   bool @\exposid{has_val}@;         // \expos
   union {
-    E @\exposid{unex}@;             // \expos
+    unexpected<E> @\exposid{unex}@; // \expos
   };
 };
 \end{codeblock}
@@ -2300,7 +2300,7 @@
 Otherwise, if \tcode{rhs.has_value()} is \tcode{true},
 destroys \exposid{unex} and sets \exposid{has_val} to \tcode{true}.
 \item
-Otherwise, equivalent to \tcode{\exposid{unex} = rhs.error()}.
+Otherwise, equivalent to \tcode{\exposid{unex} = rhs.\exposid{unex}}.
 \end{itemize}
 
 \pnum
@@ -2347,7 +2347,7 @@
 Otherwise, if \tcode{rhs.has_value()} is \tcode{true},
 destroys \exposid{unex} and sets \exposid{has_val} to \tcode{true}.
 \item
-Otherwise, equivalent to \tcode{\exposid{unex} = std::move(rhs.error())}.
+Otherwise, equivalent to \tcode{\exposid{unex} = std::move(rhs.\exposid{unex})}.
 \end{itemize}
 
 \pnum
@@ -2396,7 +2396,7 @@
 \end{codeblock}
 \item
 Otherwise, equivalent to:
-\tcode{\exposid{unex} = std::forward<GF>(e.error());}
+\tcode{\exposid{unex} = unexpected<E>(std::forward<GF>(e.error()));}
 \end{itemize}
 
 \pnum
@@ -2546,7 +2546,7 @@
 
 \pnum
 \returns
-\exposid{unex}.
+\tcode{\exposid{unex}.error()}.
 \end{itemdescr}
 
 \indexlibrarymember{error}{expected<void>}%
@@ -2562,7 +2562,7 @@
 
 \pnum
 \returns
-\tcode{std::move(\exposid{unex})}.
+\tcode{std::move(\exposid{unex}).error()}.
 \end{itemdescr}
 
 \indexlibrarymember{error_or}{expected<void>}%