FEATURE: Stream topic summaries. (#23065)

When we receive the stream parameter, we'll queue a job that periodically publishes partial updates, and after the summarization finishes, a final one with the completed version, plus metadata.

`summary-box` listens to these updates via MessageBus, and updates state accordingly.

spec/jobs/regular/stream_topic_summary_spec.rb

@@ -0,0 +1,76 @@
+# frozen_string_literal: true
+
+RSpec.describe Jobs::StreamTopicSummary do
+  subject(:job) { described_class.new }
+
+  describe "#execute" do
+    fab!(:topic) { Fabricate(:topic) }
+    let(:plugin) { Plugin::Instance.new }
+    let(:strategy) { DummyCustomSummarization.new({ summary: "dummy", chunks: [] }) }
+    fab!(:user) { Fabricate(:leader) }
+
+    before { Group.find(Group::AUTO_GROUPS[:trust_level_3]).add(user) }
+
+    before do
+      plugin.register_summarization_strategy(strategy)
+      SiteSetting.summarization_strategy = strategy.model
+    end
+
+    describe "validates params" do
+      it "does nothing if there is no topic" do
+        messages =
+          MessageBus.track_publish("/summaries/topic/#{topic.id}") do
+            job.execute(topic_id: nil, user_id: user.id)
+          end
+
+        expect(messages).to be_empty
+      end
+
+      it "does nothing if there is no user" do
+        messages =
+          MessageBus.track_publish("/summaries/topic/#{topic.id}") do
+            job.execute(topic_id: topic.id, user_id: nil)
+          end
+
+        expect(messages).to be_empty
+      end
+
+      it "does nothing if the user is not allowed to see the topic" do
+        private_topic = Fabricate(:private_message_topic)
+
+        messages =
+          MessageBus.track_publish("/summaries/topic/#{private_topic.id}") do
+            job.execute(topic_id: private_topic.id, user_id: user.id)
+          end
+
+        expect(messages).to be_empty
+      end
+    end
+
+    it "publishes updates with a partial summary" do
+      messages =
+        MessageBus.track_publish("/summaries/topic/#{topic.id}") do
+          job.execute(topic_id: topic.id, user_id: user.id)
+        end
+
+      partial_summary_update = messages.first.data
+      expect(partial_summary_update[:done]).to eq(false)
+      expect(partial_summary_update.dig(:topic_summary, :summarized_text)).to eq("dummy")
+    end
+
+    it "publishes a final update to signal we're done and provide metadata" do
+      messages =
+        MessageBus.track_publish("/summaries/topic/#{topic.id}") do
+          job.execute(topic_id: topic.id, user_id: user.id)
+        end
+
+      final_update = messages.last.data
+      expect(final_update[:done]).to eq(true)
+
+      expect(final_update.dig(:topic_summary, :algorithm)).to eq(strategy.model)
+      expect(final_update.dig(:topic_summary, :outdated)).to eq(false)
+      expect(final_update.dig(:topic_summary, :can_regenerate)).to eq(true)
+      expect(final_update.dig(:topic_summary, :new_posts_since_summary)).to be_zero
+    end
+  end
+end