Adds Flow Schedule Email Notifications

What does this MR do and why?

MR 5 (of 7) that addressses: #594180. The goal of the series: users will be able to run AI flows on a cron schedule.

This MR adds failure notifications for flow schedules, following the pipeline_schedule_owner_unavailable precedent.

• Emails::Ai::FlowSchedules mailer with failure and deactivation emails (4 templates)
• NotificationService methods that email project owners and maintainers

Emails are sent on each failure and again on 3-strike deactivation. Successful runs deliberately send nothing.

How to set up and validate locally

Prerequisites

• Rails console
• GDK and letter_opener running: http://172.16.123.1:3000/rails/letter_opener

1. Set up in Rails (create project, users, trigger and schedule):

project = FactoryBot.create(:project)
owner = FactoryBot.create(:user).tap { |u| project.add_owner(u) }
maintainer = FactoryBot.create(:user).tap { |u| project.add_maintainer(u) }
developer = FactoryBot.create(:user).tap { |u| project.add_developer(u) } # should NOT receive an email

trigger = FactoryBot.create(:ai_flow_trigger, project: project)
schedule = FactoryBot.create(:ai_flow_schedule, flow_trigger: trigger, description: 'Nightly sync')

• Note: project.creator (autogenerated by the factory) is also an owner, so you'll see 3 recipients below, not 2.

2. In rails console, call each NotificationService method directly (this MR does not wire either into a worker yet):

NotificationService.new.ai_flow_schedule_deactivated(schedule)

NotificationService.new.ai_flow_schedule_failed(schedule)

3. View the rendered emails in letter_opener_web: http://172.16.123.1:3000/rails/letter_opener.
4. Confirm:
   • Exactly three emails per call, one each to both owners and one to maintainer and none to developer.
     • Grab the recipient user IDs shown in letter_opener/Sidekiq and confirm in Rails console developer.id is absent: [owner.id, maintainer.id, developer.id].
     • e.g. [209, 210, 211], the recipients you see should include 209 and 210 (plus project.creator.id), but never 211 (developer ID).
   • Subject includes the schedule's description, e.g. Flow schedule deactivated: Nightly sync / Flow schedule failed: Nightly sync.
   • Body content matches the corresponding template (ai_flow_schedule_deactivated_email vs ai_flow_schedule_failure_email).

Related Stacked MRs (in order)

1. Adds ai_flow_schedules table for scheduled AI f... (!250227 - merged)
2. Add scheduled event type to AI flow triggers (!250805 - merged)
3. Adds Flow Schedule Model (!250809 - merged)
4. Add Flow Schedules API (!250821 - merged)
5. Adds Flow Schedule Email Notifications (!250824 - merged) (This MR)
6. Adds flow schedule execution (!250838)
7. Adds FE changes for Flow Schedules (!250843)

References

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