fix: preserve x value when re-entering edit mode

samples/dev/index.html

@@ -372,7 +372,10 @@
     function reactivateEditOnX() {
       clearStackSelection();
       if (calc.isValidIndex(0)) {
-        calc.edit(0);
+        const value = getStackValue(0);
+        calc.remove(0);
+        calc.inputValue = calc.formatNumber(value);
+        calc.isEditing = true;
       } else {
         calc.inputValue = '';
         calc.isEditing = true;
@@ -397,7 +400,7 @@
       }
 
       if (direction === 'down' && stackCursor === 0) {
-        clearStackSelection();
+        reactivateEditOnX();
       }
     }