Guarantee against data loss by preventing race condition on save

[dabura667]

Offline management of (writeable) vault items

[%E7%AF%84%E5%9B%B2%E3%82%92%E9%81%B8%E6%8A%9E_001] [%E7%AF%84%E5%9B%B2%E3%82%92%E9%81%B8%E6%8A%9E_002] Some ideas I shared on gitter.

I had a suggestion on a different issue