Challenge 2: Retry and Discard — Solution

# app/jobs/resize_image_job.rb
class ResizeImageJob < ApplicationJob
  queue_as :default
  retry_on ImageProcessingTimeout, wait: :exponentially_longer, attempts: 3
  discard_on ActiveRecord::RecordNotFound

  def perform(image_id)
    image = Image.find(image_id)
    image.resize!
  end
end

=begin
Notes:
- retry_on ImageProcessingTimeout treats a timeout as transient -- whatever
  caused the resize to take too long (a busy processing service, a
  temporarily large file) is worth trying again for, so the job retries up
  to 3 times with wait: :exponentially_longer spacing retries further apart
  each time rather than hammering the same failure immediately.
- discard_on ActiveRecord::RecordNotFound is the opposite judgment call: if
  the image was deleted before the job ran, no number of retries fixes that,
  so the job gives up on the first attempt instead of retrying a failure
  that can never succeed.
- Both declarations sit above perform, matching where queue_as already
  lives -- job-level configuration, separate from the actual work the job
  does.
=end