peta912 I mean, you can enable Storage Scopes for the default keyboard app if you really want to, by going to Settings > Privacy > Permission manager > Photos and videos / Music and audio > three dots > Show system > Keyboard.
I have never heard of a case where a prompt has been shown asking the user you enable Storage Scopes for the keyboard app. I did a search in the forums but couldn't find anything.
peta912 Could the keyboard app been compromised somehow ?
I think that making such a conclusion is premature. All you presumably saw was a system dialog. Theoretically, it could've been an app that you yourself have installed which showed you a fake permission dialog in order to trick you into giving it access to some of your files. But it would be an unprecedented occurrence for an app to pretend to be a GrapheneOS-specific system dialogue. Do you have a third-party app called "Keyboard" (not the default keyboard app) on your phone?
peta912 Could I have seen something entirely else (it went pretty quick tbh) ?
Frankly, I think that is quite likely. Especially if you are unsure of what the dialogue said.
peta912 Today I received a very curious system message , after I deleted the Vanadium cache
Are you quite sure that selecting "Clear cache" for Vanadium triggered a dialogue? When I do the same on my end, I am not presented with a dialogue.