Add temporary "non_llm_answer" strategy

This strategy (which is configured as the default for this branch) will
generate an answer without making any LLM calls.

It's for the SREs to be able to do load testing without incurring costs
from any LLM providers.

The `sleep 20` call emulates the latency that we see in a normal
LLM-based strategy.

Author: jackbot

app/jobs/answer_analysis/tag_topics_job.rb

@@ -10,18 +10,23 @@ def perform(answer_id)
       end
       return if quota_limit_reached?
 
-      result = AutoEvaluation::TopicTagger.call(answer.question_used)
+      if Rails.configuration.answer_strategy == "non_llm_answer"
+        # Temporary strategy for SREs to load test without incurring LLM costs
+        sleep 10
+      else
+        result = AutoEvaluation::TopicTagger.call(answer.question_used)
 
-      topics = answer.build_topics(
-        status: result.status,
-        primary_topic: result.primary_topic,
-        secondary_topic: result.secondary_topic,
-        error_message: result.error_message,
-      )
-      topics.assign_metrics("topic_tagger", result.metrics)
-      topics.assign_llm_response("topic_tagger", result.llm_response)
+        topics = answer.build_topics(
+          status: result.status,
+          primary_topic: result.primary_topic,
+          secondary_topic: result.secondary_topic,
+          error_message: result.error_message,
+        )
+        topics.assign_metrics("topic_tagger", result.metrics)
+        topics.assign_llm_response("topic_tagger", result.llm_response)
 
-      topics.save!
+        topics.save!
+      end
     end
   end
 end

config/application.rb

@@ -85,7 +85,7 @@ class Application < Rails::Application
 
     config.bigquery_dataset_id = ENV["BIGQUERY_DATASET"]
 
-    config.answer_strategy = ENV.fetch("ANSWER_STRATEGY", "claude_structured_answer")
+    config.answer_strategy = "non_llm_answer"
 
     config.question_topics = GovukChatPrivate.config
                                              .llm_prompts

lib/answer_composition/composer.rb

@@ -45,6 +45,14 @@ def compose_answer
           Pipeline::StructuredAnswerComposer,
           Pipeline::AnswerGuardrails,
         ])
+      when "non_llm_answer"
+        # Temporary strategy for SREs to load test without incurring LLM costs
+        sleep 20
+        context = Pipeline::Context.new(question)
+        context.abort_pipeline(
+          message: Answer::CannedResponses::LLM_CANNOT_ANSWER_MESSAGE,
+          status: "answered",
+        )
       else
         raise "Answer strategy #{answer_strategy} not configured"
       end