FEATURE: Inline topic summary. Cached version accessible to everyone. (#22551)

* FEATURE:  Inline topic summary. Cached version accessible to everyone.

Anons and non-members of the `custom_summarization_allowed_groups_map` groups can see cached summaries for any accessible topic. After the first 12 hours and if the posts to summarize have changed, allowed users clicking on the button will automatically re-generate it.

* Ensure chat summaries work and prevent model hallucinations when there are no messages.

app/controllers/topics_controller.rb

@@ -30,7 +30,6 @@ class TopicsController < ApplicationController
                    publish
                    reset_bump_date
                    set_slow_mode
-                   summary
                  ]
 
   before_action :consider_user_for_promotion, only: :show
@@ -1172,13 +1171,17 @@ class TopicsController < ApplicationController
     topic = Topic.find(params[:topic_id])
     guardian.ensure_can_see!(topic)
     strategy = Summarization::Base.selected_strategy
-    raise Discourse::NotFound.new unless strategy
 
-    raise Discourse::InvalidAccess unless strategy.can_request_summaries?(current_user)
+    if strategy.nil? || !Summarization::Base.can_see_summary?(topic, current_user)
+      raise Discourse::NotFound
+    end
 
-    RateLimiter.new(current_user, "summary", 6, 5.minutes).performed!
+    RateLimiter.new(current_user, "summary", 6, 5.minutes).performed! if current_user
 
-    hijack { render json: { summary: TopicSummarization.new(strategy).summarize(topic) } }
+    hijack do
+      summary = TopicSummarization.new(strategy).summarize(topic, current_user)
+      render json: { summary: summary&.summarized_text, summarized_on: summary&.updated_at }
+    end
   end
 
   private