Currently, if ToolBox is not given a file manager, it will open and cache one for use as needed.

This makes it hard to know when to close it (requiring ToolBox to be Closeable is a very big ugly sledgehammer) and it leads to unfortunate coupling between separate tasks created by ToolBox.

It would be better to create, use and then close temporary file managers as needed, and if a client wants to share file managers across tasks, the use of such a file manager is best handled directly by the client.