We investigated the problem further.
By design, it is not possible in Kantu to update one element in an array in the way you and I tried in the test macro above.
The reason is that a statement like "storedVars['names'][${num}] = \"Hello World!\"" will be expanded to ["cat","dog","fish","dog","??","frog","?","dog","??","horse","??elephant"][2] = "Hello World!" during runtime.
So basically, all things in target of storeEval all happen in guest page context, variables in Kantu won’t be affected. And I think we should stick to this rule.
But we found a good solution (see next post).