Build card being converted into build tree

Still need to be able to delete fillers

app/imports/api/engine/computation/utility/walkdown.js

@@ -2,7 +2,7 @@ export default function walkDown(tree, callback){
   let stack = [...tree];
   while(stack.length){
     let node = stack.pop();
-    callback(node);
+    callback(node, stack);
     stack.push(...node.children);
   }
 }