Part of my threat model is protecting my info from nosy friends and family members who might have access to my phone if I leave it unlocked for a short time, or to whom I might lend the phone to read map directions or some such. (App pinning isn't a serious option since such tasks often involve multiple apps, and also I'd rather not make it obvious that I don't trust these people.)
I'm planning to use a separate profile for private files (like intimate photos) that I rarely access. However I'm having trouble reducing the exposure of SMS(/MMS) storage. (Side note: I know that SMS is insecure when sent and in server-side storage, but my messaging contacts would be unwilling and likely incapable of using a better solution like Signal or Molly. Fortunately the friends and family members I'm worried about are neither sophisticated nor motivated enough to exploit these weaknesses of SMS. I am happy to treat SMS/MMS messages as postcards; but I wouldn't leave all the postcards I've received in plain view of everybody who came to my house.) I want to keep SMS messages I've received, but I want to keep them securely locked (or, better yet, hidden -- in a dream world, with the ability to securely hide particular threads or messages).
I was hoping to solve this by isolating the stock SMS app in a separate GrapheneOS profile that I switch to when I receive a message, but the SMS profile permission is coupled to the phone permission, so if I did this I wouldn't be able to keep my regular-use profile SMS-free without missing all phone calls.
The only other solution I can find is Silence, which encrypts its SMS/MMS storage. Silence hasn't been updated in years (though it does show recent commits for translation, so maybe it's not completely dead?). It also doesn't seem to be able to communicate across GOS profiles, so using it would lock me into using the Owner profile for regular use. But at the moment I can't find any other solution that solves my problem.
It seems like protecting saved messages from people with physical device access would be quite a common threat, and in the case of someone dealing with domestic abuse a very serious one, but I can find almost nothing about it on the web. (All the discussion of SMS seems focused on secure transmission and server-side storage, not client-side storage). Does anybody know of a good way to handle this threat using GrapheneOS or compatible tools?