lua: unary-minus/^ precedence (^ binds tighter); parse-pow-chain helper +3 tests

lib/lua/test.sh

@@ -928,6 +928,14 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 1831)
 (eval "(lua-eval-ast \"if \\\"\\\\09912\\\" == \\\"c12\\\" then return 1 else return 0 end\")")
 
+;; ── Unary-minus / ^ precedence (Lua spec: ^ tighter than -) ──
+(epoch 1840)
+(eval "(lua-eval-ast \"return -2^2\")")
+(epoch 1841)
+(eval "(lua-eval-ast \"return 2^3^2\")")
+(epoch 1842)
+(eval "(lua-eval-ast \"if -2^2 == -4 then return 1 else return 0 end\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 60 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -1401,6 +1409,11 @@ check 1821 "arg[i] access"                  '60'
 check 1830 "\\65 → A"                        '"A"'
 check 1831 "\\099 + 12 → c12"                '1'
 
+# ── Unary-minus / ^ precedence (Lua: ^ tighter than unary -) ──
+check 1840 "-2^2 = -4"                      '-4'
+check 1841 "2^3^2 = 512 (right-assoc)"      '512'
+check 1842 "-2^2 == -4 true"                '1'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL Lua-on-SX tests passed"