Hi
Temporary files get deleted both on shutdown and startup of Burp. Therefore, if you close and relaunch Burp the temporary files will not be persisted.
If you'd like to save data to persist across reloads of Burp, then check out IBurpExtenderCallbacks.saveExtensionSetting() and IBurpExtenderCallbacks.loadExtensionSetting()
Alternatively, if there's an existing extension that has a method of persisting data in a similar way to how you would like to persist your data you could have a look at how they've done it. All BApp Store extensions have their code publicly available on GitHub. You can find them
hereFor persisting information on a project level basis, extension authors have had success creating a "dummy" site map item and using that to store information.
Please let us know if you need any further assistance.