Function assert_can_view 

pub async fn assert_can_view(
    db: &SqlitePool,
    current_user: Uuid,
    destination: Destination,
) -> Result<Option<GroupRole>, Error>

Resolve a destination to whether the current user can view its contents and (for groups) what role they have. Personal scope means the user is the owner; otherwise Error::Forbidden is returned.

Errors

Returns Error::Forbidden if the user is not a member of the target group.