feat: make the rollup backfill atomic

app/services/reporting_events/backfill_service.rb

@@ -25,10 +25,13 @@ class ReportingEvents::BackfillService
   end
 
   def perform
-    delete_existing_rollups
     start_utc, end_utc = date_boundaries_in_utc
     rollup_rows = build_rollup_rows(start_utc, end_utc)
-    bulk_insert_rollups(rollup_rows) if rollup_rows.any?
+
+    ReportingEventsRollup.transaction do
+      delete_existing_rollups
+      bulk_insert_rollups(rollup_rows) if rollup_rows.any?
+    end
   end
 
   private

lib/tasks/reporting_events_rollup.rake

@@ -187,6 +187,7 @@ class ReportingEventsRollupBackfill # rubocop:disable Metrics/ClassLength
     end
 
     print_success(account, days_processed, total_days, Time.current - start_time)
+    prompt_enable_rollup_read_path(account)
   rescue StandardError => e
     print_failure(e, days_processed, total_days)
   end
@@ -201,13 +202,28 @@ class ReportingEventsRollupBackfill # rubocop:disable Metrics/ClassLength
     puts "Average per Day:      #{(elapsed_time / days_processed).round(3)} seconds"
     puts ''
     puts 'Next steps:'
-    puts "1. Enable feature flag: Account.find(#{account.id}).enable_features!('reporting_events_rollup')"
+    puts '1. Verify parity before enabling the reporting_events_rollup read path.'
     puts '2. Verify rollups in database:'
     puts "   ReportingEventsRollup.where(account_id: #{account.id}).count"
     puts '3. Test reports to compare rollup vs raw performance'
     puts color('=' * 70, :green)
   end
 
+  def prompt_enable_rollup_read_path(account)
+    if account.feature_enabled?(:reporting_events_rollup)
+      puts color('reporting_events_rollup is already enabled for this account.', :yellow, :bold)
+      return
+    end
+
+    print 'Enable reporting_events_rollup read path now? Only do this after parity verification. (y/N): '
+    confirm = $stdin.gets.to_s.chomp.downcase
+    puts ''
+    return unless %w[y yes].include?(confirm)
+
+    account.enable_features!('reporting_events_rollup')
+    puts color("Enabled reporting_events_rollup for account #{account.id}", :green, :bold)
+  end
+
   def print_failure(error, days_processed, total_days)
     puts "\n\n"
     puts color('=' * 70, :red)

spec/lib/reporting_events_rollup_backfill_spec.rb

@@ -0,0 +1,53 @@
+require 'rails_helper'
+require 'rake'
+
+Rails.application.load_tasks unless Object.const_defined?(:ReportingEventsRollupBackfill)
+
+describe ReportingEventsRollupBackfill do
+  let(:service) { described_class.new }
+  let(:account) { create(:account, reporting_timezone: 'America/New_York') }
+  let(:date) { Date.new(2026, 2, 11) }
+
+  describe '#execute_backfill' do
+    before do
+      allow(ReportingEvents::BackfillService).to receive(:backfill_date)
+      allow($stdout).to receive(:flush)
+    end
+
+    it 'prompts to enable the read path only after a successful backfill' do
+      allow(service).to receive(:print_success)
+
+      expect(service).to receive(:prompt_enable_rollup_read_path).with(account)
+
+      service.send(:execute_backfill, account, date, date, 1)
+    end
+
+    it 'does not prompt to enable the read path when backfill fails' do
+      allow(ReportingEvents::BackfillService).to receive(:backfill_date).and_raise(StandardError, 'boom')
+
+      expect(service).not_to receive(:prompt_enable_rollup_read_path)
+
+      expect do
+        service.send(:execute_backfill, account, date, date, 1)
+      end.to raise_error(SystemExit)
+    end
+  end
+
+  describe '#prompt_enable_rollup_read_path' do
+    it 'enables the feature flag when the user confirms' do
+      allow($stdin).to receive(:gets).and_return("y\n")
+
+      expect(account).to receive(:enable_features!).with('reporting_events_rollup')
+
+      service.send(:prompt_enable_rollup_read_path, account)
+    end
+
+    it 'does not enable the feature flag when the user declines' do
+      allow($stdin).to receive(:gets).and_return("n\n")
+
+      expect(account).not_to receive(:enable_features!)
+
+      service.send(:prompt_enable_rollup_read_path, account)
+    end
+  end
+end

spec/services/reporting_events/backfill_service_spec.rb

@@ -42,6 +42,82 @@ describe ReportingEvents::BackfillService do
       expect(rollup.sum_value_business_hours).to eq(0)
     end
 
+    it 'preserves existing rollups when building replacement rows fails' do
+      create(
+        :reporting_events_rollup,
+        account: account,
+        date: date,
+        dimension_type: 'account',
+        dimension_id: account.id,
+        metric: 'first_response',
+        count: 7,
+        sum_value: 700,
+        sum_value_business_hours: 350
+      )
+
+      service = described_class.new(account, date)
+      allow(service).to receive(:build_rollup_rows).and_raise(StandardError, 'boom')
+
+      expect do
+        service.perform
+      end.to raise_error(StandardError, 'boom')
+
+      rollup = ReportingEventsRollup.find_by!(
+        account_id: account.id,
+        date: date,
+        dimension_type: 'account',
+        dimension_id: account.id,
+        metric: 'first_response'
+      )
+
+      expect(rollup.count).to eq(7)
+      expect(rollup.sum_value).to eq(700)
+      expect(rollup.sum_value_business_hours).to eq(350)
+    end
+
+    it 'preserves existing rollups when replacing rows fails' do
+      create(
+        :reporting_events_rollup,
+        account: account,
+        date: date,
+        dimension_type: 'account',
+        dimension_id: account.id,
+        metric: 'first_response',
+        count: 7,
+        sum_value: 700,
+        sum_value_business_hours: 350
+      )
+
+      create_backfill_event(
+        name: 'first_response',
+        value: 100,
+        value_in_business_hours: 50,
+        user: user,
+        inbox: inbox,
+        conversation: conversation,
+        created_at: Time.utc(2026, 2, 11, 15)
+      )
+
+      service = described_class.new(account, date)
+      allow(service).to receive(:bulk_insert_rollups).and_raise(StandardError, 'boom')
+
+      expect do
+        service.perform
+      end.to raise_error(StandardError, 'boom')
+
+      rollup = ReportingEventsRollup.find_by!(
+        account_id: account.id,
+        date: date,
+        dimension_type: 'account',
+        dimension_id: account.id,
+        metric: 'first_response'
+      )
+
+      expect(rollup.count).to eq(7)
+      expect(rollup.sum_value).to eq(700)
+      expect(rollup.sum_value_business_hours).to eq(350)
+    end
+
     it 'aggregates grouped rows without instantiating reporting events' do
       second_user = create(:user, account: account)
       second_inbox = create(:inbox, account: account)