Duo Chat: Output non-recoverable errors

What does this MR do and why?

The MR introduces the output of the potential non-recoverable errors in Duo Chat.

Screenshots or screen recordings

When sending the same /clean prompt into chat.

Before	After

How to set up and validate locally

• Set up GitLab Duo Chat. Mainly, you're interested in running the automatic script
• Apply patch which guarantees an error when sending /clean:

diff --git a/ee/app/services/llm/chat_service.rb b/ee/app/services/llm/chat_service.rb
index 8a2030952e94..bc93cce9c4ee 100644
--- a/ee/app/services/llm/chat_service.rb
+++ b/ee/app/services/llm/chat_service.rb
@@ -9,7 +9,11 @@ def ai_action
     end
 
     def perform
-      prompt_message.save!
+      if prompt_message.chat_cleaned? 
+        prompt_message.clean!
+      else
+        prompt_message.save!  
+      end
       GraphqlTriggers.ai_completion_response(prompt_message)
       schedule_completion_worker unless prompt_message.conversation_reset?
     end
diff --git a/ee/lib/gitlab/llm/chat_message.rb b/ee/lib/gitlab/llm/chat_message.rb
index 787487f7518e..7769a0117a64 100644
--- a/ee/lib/gitlab/llm/chat_message.rb
+++ b/ee/lib/gitlab/llm/chat_message.rb
@@ -4,14 +4,23 @@ module Gitlab
   module Llm
     class ChatMessage < AiMessage
       RESET_MESSAGE = '/reset'
+      CLEAN_MESSAGE = '/clean'
 
       def save!
         ChatStorage.new(user).add(self)
       end
 
+      def clean!
+        raise "500 Internal Server Error"
+      end
+
       def conversation_reset?
         content == RESET_MESSAGE
       end
+
+      def chat_cleaned?
+        content == CLEAN_MESSAGE
+      end
     end
   end
 end

• Start the chat from the left-hand navigation panel in "Help -> GitLab Duo Chat"
• Send /clean message in the chat

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.