I just build and installed your filetest.aia, changed nothing, and it works without the slightest problem:
OK now I found what goes on. It's not something new. It's been mentioned by @Anke multiple times. Let me try to say it simply: files saved in shared folders, belong to the installation of the app that created them. other apps (or even a re-installation of the same app) cannot overwrite them. So it will give you these permission errors (EACCES) if the installation of the app is different than the one that created the files in the first place.
The problem is not only for overwriting/deleting the file though. I still haven't managed to read its content.
It appears that we cannot:
- read a saved file in shared folder (file component says not found)
- overwrite/delete a saved file in shared folder if A) we reinstall the app, B) using another app
I haven't tested with DefaultFileScope:Legacy though. If I understand right, these problems just go away when you switch to legacy. Haven't tested. (edit: they don't. see the following link)
Check my latest guide on working with shared folders (written today).