Apply measure now uses a temp model and sandbox to protect the working model. However, we need a way to access files in the model's companion directory. Use cases are:

• Write an html report to the reports directory
• Write a csv file to the model's data dir
• Read a file from the model's data dir

We need to make sure to revert all changes if the user cancels. Suggest that we initialize a temp model companion dir with all files, then merge that back on accept.