FIX: Don't delete previous messages when we're inside the `sent_recently` window. (#18239)

`delete_previous!` deletes existing topics even when we cannot send a new one due to the `limit_once_per` option. The dashboard problems PM gets deleted the next time the job runs (30 minutes), so the inbox could be empty when
admins click on the summary notification.

app/services/group_message.rb

@@ -27,23 +27,23 @@ class GroupMessage
   end
 
   def create
-    unless sent_recently?
-      post = PostCreator.create(
-        Discourse.system_user,
-        target_group_names: [@group_name],
-        archetype: Archetype.private_message,
-        subtype: TopicSubtype.system_message,
-        title: I18n.t("system_messages.#{@message_type}.subject_template", message_params),
-        raw: I18n.t("system_messages.#{@message_type}.text_body_template", message_params)
-      )
-      remember_message_sent
-      post
-    else
-      false
-    end
+    return false if sent_recently?
+
+    post = PostCreator.create(
+      Discourse.system_user,
+      target_group_names: [@group_name],
+      archetype: Archetype.private_message,
+      subtype: TopicSubtype.system_message,
+      title: I18n.t("system_messages.#{@message_type}.subject_template", message_params),
+      raw: I18n.t("system_messages.#{@message_type}.text_body_template", message_params)
+    )
+    remember_message_sent
+    post
   end
 
-  def delete_previous!(match_raw: true)
+  def delete_previous!(respect_sent_recently: true, match_raw: true)
+    return false if respect_sent_recently && sent_recently?
+
     posts = Post
       .joins(topic: { topic_allowed_groups: :group })
       .where(topic: {

spec/jobs/dashboard_stats_spec.rb

@@ -4,6 +4,7 @@ RSpec.describe ::Jobs::DashboardStats do
   let(:group_message) { GroupMessage.new(Group[:admins].name, :dashboard_problems, limit_once_per: 7.days.to_i) }
 
   def clear_recently_sent!
+    # We won't immediately create new PMs due to the limit_once_per option, reset the value for testing purposes.
     Discourse.redis.del(group_message.sent_recently_key)
   end
 
@@ -31,6 +32,13 @@ RSpec.describe ::Jobs::DashboardStats do
     expect(new_topic.title).to eq(old_topic.title)
   end
 
+  it 'respects the sent_recently? check when deleting previous message' do
+    Discourse.redis.setex(AdminDashboardData.problems_started_key, 14.days.to_i, 3.days.ago)
+    expect { described_class.new.execute({}) }.to change { Topic.count }.by(1)
+
+    expect { described_class.new.execute({}) }.not_to change { Topic.count }
+  end
+
   it 'duplicates message if previous one has replies' do
     Discourse.redis.setex(AdminDashboardData.problems_started_key, 14.days.to_i, 3.days.ago)
     expect { described_class.new.execute({}) }.to change { Topic.count }.by(1)