feat: validate sender before creating campaign (#10934)

spec/models/campaign_spec.rb

@@ -114,4 +114,26 @@ RSpec.describe Campaign do
       end
     end
   end
+
+  context 'when validating sender' do
+    let(:account) { create(:account) }
+    let(:user) { create(:user, account: account) }
+    let(:web_widget) { create(:channel_widget, account: account) }
+    let(:inbox) { create(:inbox, channel: web_widget, account: account) }
+
+    it 'allows sender from the same account' do
+      campaign = build(:campaign, inbox: inbox, account: account, sender: user)
+      expect(campaign).to be_valid
+    end
+
+    it 'does not allow sender from different account' do
+      other_account = create(:account)
+      other_user = create(:user, account: other_account)
+      campaign = build(:campaign, inbox: inbox, account: account, sender: other_user)
+      expect(campaign).not_to be_valid
+      expect(campaign.errors[:sender_id]).to include(
+        'must belong to the same account as the campaign'
+      )
+    end
+  end
 end