Exclude archived stacks from the scheduler loops

Stack.schedule_continuous_delivery and Stack.refresh_deployed_revisions
run every minute from the host application's scheduler, but neither
scope excluded archived stacks. Archiving locks a stack, so the jobs
were guaranteed no-ops: ContinuousDeliveryJob bails on the lock and
FetchDeployedRevisionJob refreshes state nobody can see.

At Shopify's scale that was ~1300 archived stacks enqueuing ~2000
no-op ContinuousDeliveryJobs per minute, plus full git clones from
FetchDeployedRevisionJob for archived stacks with fetch steps, all on
the same worker pool as deploys.

Unarchiving already triggers a GithubSyncJob via
sync_github_if_necessary, so a revived stack re-enters both loops
naturally.

Author: aqeelvn

app/models/shipit/stack.rb

@@ -117,11 +117,11 @@ def sync_github_if_necessary
     )
 
     def self.refresh_deployed_revisions
-      find_each.select(&:supports_fetch_deployed_revision?).each(&:async_refresh_deployed_revision)
+      not_archived.find_each.select(&:supports_fetch_deployed_revision?).each(&:async_refresh_deployed_revision)
     end
 
     def self.schedule_continuous_delivery
-      where(continuous_deployment: true).find_each do |stack|
+      not_archived.where(continuous_deployment: true).find_each do |stack|
         ContinuousDeliveryJob.perform_later(stack)
       end
     end

test/models/shipit/stack_test.rb

@@ -11,6 +11,36 @@ def setup
       GithubHook.any_instance.stubs(:teardown!)
     end
 
+    test ".schedule_continuous_delivery skips archived stacks" do
+      archived = shipit_stacks(:archived_6hours_ago)
+      archived.update!(continuous_deployment: true)
+      @stack.update!(continuous_deployment: true)
+
+      Stack.schedule_continuous_delivery
+
+      enqueued_args = enqueued_jobs
+                      .select { |job| job[:job] == ContinuousDeliveryJob }
+                      .map { |job| job[:args].to_s }
+      assert enqueued_args.any? { |args| args.include?("Stack/#{@stack.id}") },
+             "expected a ContinuousDeliveryJob for the active stack"
+      refute enqueued_args.any? { |args| args.include?("Stack/#{archived.id}") },
+             "archived stacks must not trigger continuous delivery"
+    end
+
+    test ".refresh_deployed_revisions skips archived stacks" do
+      archived = shipit_stacks(:archived_6hours_ago)
+      archived.update!(cached_deploy_spec: DeploySpec.new('fetch' => ['echo 1']))
+
+      Stack.refresh_deployed_revisions
+
+      enqueued_args = enqueued_jobs
+                      .select { |job| job[:job] == FetchDeployedRevisionJob }
+                      .map { |job| job[:args].to_s }
+      assert enqueued_args.any?, "expected FetchDeployedRevisionJobs for active stacks with fetch steps"
+      refute enqueued_args.any? { |args| args.include?("Stack/#{archived.id}") },
+             "archived stacks must not refresh deployed revisions"
+    end
+
     test "branch defaults to default branch name" do
       @stack.branch = ""
       Shipit.github.api.expects(:repo).with("shopify/shipit-engine").returns(