chore: Migrate mailers from the worker to jobs (#12331)

Previously, email replies were handled inside workers. There was no
execution logs. This meant if emails silently failed (as reported by a
customer), we had no way to trace where the issue happened, the only
assumption was “no error = mail sent.”

By moving email handling into jobs, we now have proper execution logs
for each attempt. This makes it easier to debug delivery issues and
would have better visibility when investigating customer reports.

Fixes
https://linear.app/chatwoot/issue/CW-5538/emails-are-not-sentdelivered-to-the-contact

---------

Co-authored-by: Sojan Jose <sojan@pepalo.com>
Co-authored-by: Shivam Mishra <scm.mymail@gmail.com>

spec/services/messages/send_email_notification_service_spec.rb

@@ -0,0 +1,190 @@
+require 'rails_helper'
+
+describe Messages::SendEmailNotificationService do
+  let(:account) { create(:account) }
+  let(:conversation) { create(:conversation, account: account) }
+  let(:message) { create(:message, conversation: conversation, message_type: 'outgoing') }
+  let(:service) { described_class.new(message: message) }
+
+  describe '#perform' do
+    context 'when email notification should be sent' do
+      let(:inbox) { create(:inbox, account: account, channel: create(:channel_widget, account: account, continuity_via_email: true)) }
+      let(:conversation) { create(:conversation, account: account, inbox: inbox) }
+
+      before do
+        conversation.contact.update!(email: 'test@example.com')
+        allow(Redis::Alfred).to receive(:set).and_return(true)
+        allow(ConversationReplyEmailWorker).to receive(:perform_in)
+      end
+
+      it 'schedules ConversationReplyEmailWorker' do
+        service.perform
+
+        expect(ConversationReplyEmailWorker).to have_received(:perform_in).with(
+          2.minutes,
+          conversation.id,
+          message.id
+        )
+      end
+
+      it 'atomically sets redis key to prevent duplicate emails' do
+        expected_key = format(Redis::Alfred::CONVERSATION_MAILER_KEY, conversation_id: conversation.id)
+
+        service.perform
+
+        expect(Redis::Alfred).to have_received(:set).with(expected_key, message.id, nx: true, ex: 1.hour.to_i)
+      end
+
+      context 'when redis key already exists' do
+        before do
+          allow(Redis::Alfred).to receive(:set).and_return(false)
+        end
+
+        it 'does not schedule worker' do
+          service.perform
+
+          expect(ConversationReplyEmailWorker).not_to have_received(:perform_in)
+        end
+
+        it 'attempts atomic set once' do
+          service.perform
+
+          expect(Redis::Alfred).to have_received(:set).once
+        end
+      end
+    end
+
+    context 'when handling concurrent requests' do
+      let(:inbox) { create(:inbox, account: account, channel: create(:channel_widget, account: account, continuity_via_email: true)) }
+      let(:conversation) { create(:conversation, account: account, inbox: inbox) }
+
+      before do
+        conversation.contact.update!(email: 'test@example.com')
+      end
+
+      it 'prevents duplicate workers under race conditions' do
+        # Create 5 threads that simultaneously try to enqueue workers for the same conversation
+        threads = Array.new(5) do
+          Thread.new do
+            msg = create(:message, conversation: conversation, message_type: 'outgoing')
+            described_class.new(message: msg).perform
+          end
+        end
+
+        threads.each(&:join)
+
+        # Only ONE worker should be scheduled despite 5 concurrent attempts
+        jobs_for_conversation = ConversationReplyEmailWorker.jobs.select { |job| job['args'].first == conversation.id }
+        expect(jobs_for_conversation.size).to eq(1)
+      end
+    end
+
+    context 'when email notification should not be sent' do
+      before do
+        allow(ConversationReplyEmailWorker).to receive(:perform_in)
+      end
+
+      context 'when message is not email notifiable' do
+        let(:message) { create(:message, conversation: conversation, message_type: 'incoming') }
+
+        it 'does not schedule worker' do
+          service.perform
+
+          expect(ConversationReplyEmailWorker).not_to have_received(:perform_in)
+        end
+      end
+
+      context 'when contact has no email' do
+        let(:inbox) { create(:inbox, account: account, channel: create(:channel_widget, account: account, continuity_via_email: true)) }
+        let(:conversation) { create(:conversation, account: account, inbox: inbox) }
+
+        before do
+          conversation.contact.update!(email: nil)
+        end
+
+        it 'does not schedule worker' do
+          service.perform
+
+          expect(ConversationReplyEmailWorker).not_to have_received(:perform_in)
+        end
+      end
+
+      context 'when channel does not support email notifications' do
+        let(:inbox) { create(:inbox, account: account, channel: create(:channel_sms, account: account)) }
+        let(:conversation) { create(:conversation, account: account, inbox: inbox) }
+
+        before do
+          conversation.contact.update!(email: 'test@example.com')
+        end
+
+        it 'does not schedule worker' do
+          service.perform
+
+          expect(ConversationReplyEmailWorker).not_to have_received(:perform_in)
+        end
+      end
+    end
+  end
+
+  describe '#should_send_email_notification?' do
+    context 'with WebWidget channel' do
+      let(:inbox) { create(:inbox, account: account, channel: create(:channel_widget, account: account, continuity_via_email: true)) }
+      let(:conversation) { create(:conversation, account: account, inbox: inbox) }
+
+      before do
+        conversation.contact.update!(email: 'test@example.com')
+      end
+
+      it 'returns true when continuity_via_email is enabled' do
+        expect(service.send(:should_send_email_notification?)).to be true
+      end
+
+      context 'when continuity_via_email is disabled' do
+        let(:inbox) { create(:inbox, account: account, channel: create(:channel_widget, account: account, continuity_via_email: false)) }
+
+        it 'returns false' do
+          expect(service.send(:should_send_email_notification?)).to be false
+        end
+      end
+    end
+
+    context 'with API channel' do
+      let(:inbox) { create(:inbox, account: account, channel: create(:channel_api, account: account)) }
+      let(:conversation) { create(:conversation, account: account, inbox: inbox) }
+
+      before do
+        conversation.contact.update!(email: 'test@example.com')
+        allow(account).to receive(:feature_enabled?).and_return(false)
+        allow(account).to receive(:feature_enabled?).with('email_continuity_on_api_channel').and_return(true)
+      end
+
+      it 'returns true when email_continuity_on_api_channel feature is enabled' do
+        expect(service.send(:should_send_email_notification?)).to be true
+      end
+
+      context 'when email_continuity_on_api_channel feature is disabled' do
+        before do
+          allow(account).to receive(:feature_enabled?).and_return(false)
+          allow(account).to receive(:feature_enabled?).with('email_continuity_on_api_channel').and_return(false)
+        end
+
+        it 'returns false' do
+          expect(service.send(:should_send_email_notification?)).to be false
+        end
+      end
+    end
+
+    context 'with other channels' do
+      let(:inbox) { create(:inbox, account: account, channel: create(:channel_email, account: account)) }
+      let(:conversation) { create(:conversation, account: account, inbox: inbox) }
+
+      before do
+        conversation.contact.update!(email: 'test@example.com')
+      end
+
+      it 'returns false' do
+        expect(service.send(:should_send_email_notification?)).to be false
+      end
+    end
+  end
+end