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gitui to have access to the personal files ~/.gitconfig as it is required for the snaps core functionality. Also since gitui is the clear owner of the file ~/.config/gitui/*, so +1 on granting autoconnection of personal-files interface.
Whilst this request looks reasonable, the convention for personal-files is to name the interface after what is being accessed - in this case I think it would be best to split this into two separate personal-files instances: