test: Add focused Captain response lifecycle logs (#15364)

## What changed

This pull request adds three focused log emitters for Captain V2
response jobs:

* `job_dequeued` when Sidekiq fetches the job from Redis
* `job_skipped` when the conversation is not Pending at the first job
guard
* `response_discarded` when a newer customer message exists before model
generation

The dequeue middleware identifies V2 jobs by the triggering message ID
in the third serialized Active Job argument. It does not log Captain V1
or other Sidekiq jobs.

## Why

Recent production incidents have an enqueue record but no later job
record. Active Job `Performing` and `Performed` logs are now available
temporarily, but they do not show whether Sidekiq fetched a job before a
worker disappeared.

The dequeue log closes that gap. The two application logs explain the
early exits that otherwise produce no model trace.

The production root cause remains unresolved. This pull request adds
evidence for the next occurrence and does not change Captain response
behavior.

## Log volume

A Captain V2 response job adds one dequeue line. The other two lines
occur only on an early status skip or a pre-generation burst discard.
Existing Active Job, Langfuse, completion, failure, handoff, and usage
logs cover later stages.

## Validation

* Ruby syntax checks passed for the four implementation files.
* RuboCop found no offenses in the four implementation files.
* No new specs were added because this is temporary diagnostic logging
with no response behavior change.

config/initializers/sidekiq.rb

@@ -1,4 +1,5 @@
 require Rails.root.join('lib/redis/config')
+require Rails.root.join('lib/captain_response_dequeued_logger')
 
 schedule_file = 'config/schedule.yml'
 
@@ -18,10 +19,10 @@ end
 Sidekiq.configure_server do |config|
   config.redis = Redis::Config.app
 
-  if ActiveModel::Type::Boolean.new.cast(ENV.fetch('ENABLE_SIDEKIQ_DEQUEUE_LOGGER', false))
-    config.server_middleware do |chain|
-      chain.add ChatwootDequeuedLogger
-    end
+  config.server_middleware do |chain|
+    chain.add CaptainResponseDequeuedLogger
+
+    chain.add ChatwootDequeuedLogger if ActiveModel::Type::Boolean.new.cast(ENV.fetch('ENABLE_SIDEKIQ_DEQUEUE_LOGGER', false))
   end
 
   # skip the default start stop logging

enterprise/app/jobs/captain/conversation/response_builder_job.rb

@@ -3,6 +3,7 @@ class Captain::Conversation::ResponseBuilderJob < ApplicationJob
   include Captain::Conversation::V1FalsePromiseHandler
   include Captain::Conversation::V2LifecycleEvents
   include Captain::Conversation::MessageBuilder
+  include Captain::Conversation::ResponseLifecycleLogging
 
   MAX_MESSAGE_LENGTH = 10_000
   retry_on ActiveStorage::FileNotFoundError, attempts: 3, wait: 2.seconds
@@ -14,12 +15,13 @@ class Captain::Conversation::ResponseBuilderJob < ApplicationJob
     @assistant = assistant
     @responding_to_message_id = responding_to_message_id if captain_v2_enabled?
 
-    return unless conversation_pending?
+    return log_non_pending unless conversation_pending?
 
     Current.executed_by = @assistant
 
     return generate_and_process_response unless captain_v2_enabled?
-    return if newer_customer_message_arrived?
+
+    return log_pre_generation_discard if newer_customer_message_arrived?
 
     generate_response_with_v2
   rescue ActiveStorage::FileNotFoundError, Faraday::BadRequestError => e
@@ -223,11 +225,6 @@ class Captain::Conversation::ResponseBuilderJob < ApplicationJob
     )
   end
 
-  def conversation_pending?
-    status = Conversation.uncached { Conversation.where(id: @conversation.id).pick(:status) }
-    status == 'pending' || status == Conversation.statuses[:pending]
-  end
-
   def newer_customer_message_arrived?
     return false if @responding_to_message_id.blank?
 

enterprise/app/services/captain/conversation/response_lifecycle_logging.rb

@@ -0,0 +1,24 @@
+module Captain::Conversation::ResponseLifecycleLogging
+  private
+
+  def conversation_pending?
+    @observed_conversation_status = Conversation.uncached { Conversation.where(id: @conversation.id).pick(:status) }
+    @observed_conversation_status == 'pending' || @observed_conversation_status == Conversation.statuses[:pending]
+  end
+
+  def log_non_pending
+    return if @responding_to_message_id.nil?
+
+    Rails.logger.info(
+      "[CAPTAIN][ResponseLifecycle] event=job_skipped reason=conversation_not_pending conversation_id=#{@conversation.id} " \
+      "responding_to_message_id=#{@responding_to_message_id} conversation_status=#{@observed_conversation_status}"
+    )
+  end
+
+  def log_pre_generation_discard
+    Rails.logger.info(
+      '[CAPTAIN][ResponseLifecycle] event=response_discarded reason=newer_customer_message_before_generation ' \
+      "conversation_id=#{@conversation.id} responding_to_message_id=#{@responding_to_message_id}"
+    )
+  end
+end

lib/captain_response_dequeued_logger.rb

@@ -0,0 +1,26 @@
+# Records the Sidekiq fetch boundary for Captain response jobs without logging every job.
+class CaptainResponseDequeuedLogger
+  JOB_CLASS = 'Captain::Conversation::ResponseBuilderJob'.freeze
+
+  def call(_worker, job, queue)
+    log_dequeued(job, queue) if captain_v2_response_job?(job)
+    yield
+  end
+
+  private
+
+  def log_dequeued(job, queue)
+    active_job_id = job.dig('args', 0, 'job_id')
+    responding_to_message_id = job.dig('args', 0, 'arguments', 2)
+    Sidekiq.logger.info(
+      "[CAPTAIN][ResponseLifecycle] event=job_dequeued active_job_id=#{active_job_id} provider_job_id=#{job['jid']} " \
+      "responding_to_message_id=#{responding_to_message_id} queue=#{queue}"
+    )
+  end
+
+  def captain_v2_response_job?(job)
+    return false unless job['wrapped'] == JOB_CLASS
+
+    !job.dig('args', 0, 'arguments', 2).nil?
+  end
+end