FIX: Keep AI bot PM titles working once the bot's edit budget is spent (#42523)

Previously, automatic AI bot conversation titles were saved through
`PostRevisor` without bypassing the edit rate limiter, so each one
counted against the bot account's daily allowance. Agent bot users are
TL4 but not staff, so unlike the system user they are not exempt — once
a busy bot spent its allowance the limiter raised inside the enclosing
transaction, the title write was rolled back, and conversations were
left as "[Untitled AI bot PM]" while replies carried on working.
Reported by a customer who noticed exactly `max_edits_per_day` × the TL4
multiplier successful titles in a day, and none after.

This change passes `bypass_rate_limiter` on the title and
regenerate-reply paths, moves `bypass_bump`/`skip_validations` in the
LLM tagger and triage automations out of the fields hash and into the
options hash where `PostRevisor` actually reads them, and makes title
generation resilient to an empty or over-long model response by falling
back to an excerpt of the member's own first post, truncating to a valid
length, and only announcing the title over MessageBus once the save
succeeded.

plugins/discourse-ai/lib/ai_bot/playground.rb

@@ -8,6 +8,7 @@ module DiscourseAi
       # 10 minutes is enough for vast majority of cases
       # there is a small chance that some reasoning models may take longer
       MAX_STREAM_DELAY_SECONDS = 600
+      FALLBACK_TITLE_LENGTH = 80
 
       attr_reader :bot
 
@@ -295,12 +296,33 @@ module DiscourseAi
           DiscourseAi::Completions::Llm.text_from_response(
             bot.llm.generate(title_prompt, user: user, feature_name: "bot_title"),
           )
-        new_title = new_title.strip.split("\n").last
+        new_title = new_title.to_s.strip.split("\n").last.to_s
+        new_title = new_title.delete_prefix('"').delete_suffix('"')
 
-        PostRevisor.new(post.topic.first_post, post.topic).revise!(
-          bot.bot_user,
-          title: new_title.sub(/\A"/, "").sub(/"\Z/, ""),
-        )
+        first_post = post.topic.first_post
+
+        if new_title.blank?
+          new_title =
+            PrettyText.excerpt(
+              first_post.cooked,
+              FALLBACK_TITLE_LENGTH,
+              strip_links: true,
+              text_entities: true,
+            )
+        end
+
+        return if new_title.blank?
+
+        new_title = new_title.truncate(SiteSetting.max_topic_title_length, separator: /\s/)
+
+        revised =
+          PostRevisor.new(first_post, post.topic).revise!(
+            bot.bot_user,
+            { title: new_title },
+            bypass_rate_limiter: true,
+          )
+
+        return if !revised
 
         allowed_users = post.topic.topic_allowed_users.pluck(:user_id)
         MessageBus.publish(
@@ -313,6 +335,8 @@ module DiscourseAi
           { title: post.topic.title, topic_id: post.topic.id },
           user_ids: allowed_users,
         )
+      rescue StandardError => e
+        Discourse.warn_exception(e, message: "Discourse AI: Unable to generate title")
       end
 
       def reply_to_chat_message(message, channel, context_post_ids)
@@ -689,6 +713,7 @@ module DiscourseAi
             { raw: reply },
             skip_validations: true,
             force_new_version: true,
+            bypass_rate_limiter: true,
           )
           save_ai_custom_fields(reply_post, authorization_user_id: authorization_user_id)
         else

plugins/discourse-ai/lib/ai_bot/stream_reply_custom_tools_session.rb

@@ -543,11 +543,7 @@ module DiscourseAi
           agent_class = DiscourseAi::Agents::Agent.find_by(id: @agent.id, user: @current_user)
           if agent_class
             bot = DiscourseAi::Agents::Bot.as(@reply_user, agent: agent_class.new, model: llm_model)
-            begin
-              DiscourseAi::AiBot::Playground.new(bot).title_playground(reply_post, @user)
-            rescue StandardError => e
-              Discourse.warn_exception(e, message: "Discourse AI: Unable to generate stream title")
-            end
+            DiscourseAi::AiBot::Playground.new(bot).title_playground(reply_post, @user)
           end
         end
       end

plugins/discourse-ai/lib/automation/llm_tagger.rb

@@ -189,9 +189,12 @@ module DiscourseAi
         first_post = topic.posts.where(post_number: 1).first
         return unless first_post
 
-        changes = { tags: all_tags, bypass_bump: true, skip_validations: true }
-
-        first_post.revise(Discourse.system_user, changes)
+        first_post.revise(
+          Discourse.system_user,
+          { tags: all_tags },
+          bypass_bump: true,
+          skip_validations: true,
+        )
       end
     end
   end

plugins/discourse-ai/lib/automation/llm_triage.rb

@@ -216,9 +216,12 @@ module DiscourseAi
 
           if changes.present?
             first_post = post.topic.posts.where(post_number: 1).first
-            changes[:bypass_bump] = true
-            changes[:skip_validations] = true
-            first_post.revise(Discourse.system_user, changes)
+            first_post.revise(
+              Discourse.system_user,
+              changes,
+              bypass_bump: true,
+              skip_validations: true,
+            )
           end
 
           post.topic.update!(visible: false) if hide_topic

plugins/discourse-ai/spec/lib/automation/llm_tagger_spec.rb

@@ -66,8 +66,9 @@ RSpec.describe DiscourseAi::Automation::LlmTagger do
       Tag.find_by(name: "question")&.update!(public_topic_count: 1)
     end
 
-    it "processes a post and applies appropriate tags" do
+    it "processes a post and applies appropriate tags without bumping the topic" do
       mock_response = { "tags" => ["bug"], "confidence" => 90 }.to_json
+      bumped_at = topic.bumped_at
 
       DiscourseAi::Completions::Llm.with_prepared_responses([mock_response]) do
         described_class.handle(
@@ -83,6 +84,7 @@ RSpec.describe DiscourseAi::Automation::LlmTagger do
       end
 
       expect(topic.reload.tags.map(&:name)).to include("bug")
+      expect(topic.bumped_at).to eq_time(bumped_at)
     end
 
     it "includes document uploads independently from image uploads" do

plugins/discourse-ai/spec/lib/modules/ai_bot/playground_spec.rb

@@ -1131,6 +1131,80 @@ RSpec.describe DiscourseAi::AiBot::Playground do
         expect(pm.reload.title).to eq(expected_response)
       end
     end
+
+    it "falls back to an excerpt of the first post when the model returns nothing" do
+      DiscourseAi::Completions::Llm.with_prepared_responses([""]) do
+        playground.title_playground(third_post, user)
+      end
+
+      expect(pm.reload.title).to eq(first_post.raw)
+    end
+
+    it "truncates a title the model returns too long to be valid" do
+      long_title = "word " * 100
+
+      DiscourseAi::Completions::Llm.with_prepared_responses([long_title]) do
+        playground.title_playground(third_post, user)
+      end
+
+      expect(pm.reload.title.length).to be <= SiteSetting.max_topic_title_length
+      expect(pm.reload.title.downcase).to start_with("word word")
+    end
+
+    it "does not announce a title that was not saved" do
+      PostRevisor.any_instance.stubs(:revise!).returns(false)
+
+      messages =
+        MessageBus.track_publish("/discourse-ai/ai-bot/topic-titles") do
+          DiscourseAi::Completions::Llm.with_prepared_responses([expected_response]) do
+            playground.title_playground(third_post, user)
+          end
+        end
+
+      expect(messages).to be_empty
+      expect(pm.reload.title).to eq("This is my special PM")
+    end
+
+    it "logs and swallows errors instead of propagating them to the caller" do
+      PostRevisor.any_instance.stubs(:revise!).raises(StandardError.new("boom"))
+      Discourse.expects(:warn_exception).once
+
+      DiscourseAi::Completions::Llm.with_prepared_responses([expected_response]) do
+        expect { playground.title_playground(third_post, user) }.to_not raise_error
+      end
+    end
+
+    context "when the bot user's daily edit allowance is exhausted" do
+      fab!(:agent) { Fabricate(:ai_agent, enabled: false) }
+      fab!(:agent_user) { agent.create_user! }
+
+      let(:agent_playground) do
+        described_class.new(
+          DiscourseAi::Agents::Bot.as(agent_user, agent: agent.class_instance.new, model: claude_2),
+        )
+      end
+
+      before do
+        RateLimiter.enable
+        SiteSetting.editing_grace_period = 0
+        SiteSetting.max_edits_per_day = 1
+        SiteSetting.tl4_additional_edits_per_day_multiplier = 1
+      end
+
+      it "still updates the title" do
+        expect(agent_user.trust_level).to eq(TrustLevel[4])
+        expect(agent_user.staff?).to eq(false)
+
+        scratch_post = Fabricate(:post, user: agent_user)
+        PostRevisor.new(scratch_post).revise!(agent_user, raw: "using up the daily allowance")
+
+        DiscourseAi::Completions::Llm.with_prepared_responses([expected_response]) do
+          agent_playground.title_playground(third_post, user)
+        end
+
+        expect(pm.reload.title).to eq(expected_response)
+      end
+    end
   end
 
   describe "#reply_to" do

plugins/discourse-ai/spec/lib/modules/automation/llm_triage_spec.rb

@@ -43,8 +43,9 @@ describe DiscourseAi::Automation::LlmTriage do
     expect(post.topic.reload.visible).to eq(false)
   end
 
-  it "can categorize topics on triage" do
+  it "can categorize topics on triage without bumping the topic" do
     category = Fabricate(:category)
+    bumped_at = post.topic.bumped_at
 
     DiscourseAi::Completions::Llm.with_prepared_responses(["bad"]) do
       triage(
@@ -57,6 +58,7 @@ describe DiscourseAi::Automation::LlmTriage do
     end
 
     expect(post.topic.reload.category_id).to eq(category.id)
+    expect(post.topic.bumped_at).to eq_time(bumped_at)
   end
 
   it "can reply to topics on triage" do