lua: decimal string escapes \\ddd + control escapes (\\a/\\b/\\f/\\v) +2 tests

lib/lua/test.sh

@@ -922,6 +922,12 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 1821)
 (eval "(lua-eval-ast \"function f(a, ...) return arg[1] + arg[2] + arg[3] end return f({}, 10, 20, 30)\")")
 
+;; ── Decimal-escape strings ────────────────────────────────────
+(epoch 1830)
+(eval "(lua-eval-ast \"return \\\"\\\\65\\\"\")")
+(epoch 1831)
+(eval "(lua-eval-ast \"if \\\"\\\\09912\\\" == \\\"c12\\\" then return 1 else return 0 end\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 60 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -1391,6 +1397,10 @@ check 1812 "elseif local shadows"           '10'
 check 1820 "arg.n in vararg fn"             '3'
 check 1821 "arg[i] access"                  '60'
 
+# ── Decimal-escape strings ───────────────────────────────────
+check 1830 "\\65 → A"                        '"A"'
+check 1831 "\\099 + 12 → c12"                '1'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL Lua-on-SX tests passed"