A new branch created for a confidential issue is named `<id>-confidential-issue`.

app/models/issue.rb

@@ -158,7 +158,7 @@ class Issue < ActiveRecord::Base
   def to_branch_name
     if self.confidential?
-      "issue-#{iid}"
+      "#{iid}-confidential-issue"
     else
       "#{iid}-#{title.parameterize}"
     end

spec/models/issue_spec.rb

@@ -248,7 +248,7 @@ describe Issue, models: true do
     it "does not contain the issue title if confidential" do
       issue = create(:issue, title: 'testing-issue', confidential: true)
-      expect(issue.to_branch_name).to match /\Aissue/
+      expect(issue.to_branch_name).to match /confidential-issue\z/
     end
   end
 end