perf: reuse resolved count for reopen rate (#15122)

This improves the Captain overview by loading reporting metrics and FAQ
stats from separate endpoints. Range changes now refresh only the
metrics, while reopen-rate calculation reuses the resolved conversation
count to avoid redundant database queries.

## What changed

- Split Captain overview metrics and FAQ stats into separate APIs.
- Fetch FAQ stats independently from range-based metrics.
- Reuse resolved conversation totals when calculating reopen rate.
- Skip the reopen query when there are no resolved conversations.

enterprise/app/builders/captain/assistant_stats_builder.rb

@@ -37,6 +37,23 @@ class Captain::AssistantStatsBuilder
     build_metrics(current, previous)
   end
 
+  # Approved/pending FAQ counts and the document total in a single round trip.
+  def faq_stats
+    approved, pending, documents = Captain::AssistantResponse.by_assistant(assistant.id).reorder(nil).pick(
+      Arel.sql("COUNT(*) FILTER (WHERE status = #{Captain::AssistantResponse.statuses['approved']})"),
+      Arel.sql("COUNT(*) FILTER (WHERE status = #{Captain::AssistantResponse.statuses['pending']})"),
+      Arel.sql("(SELECT COUNT(*) FROM captain_documents WHERE assistant_id = #{assistant.id.to_i})")
+    )
+    total = approved + pending
+
+    {
+      approved: approved,
+      pending: pending,
+      documents: documents,
+      coverage: total.zero? ? 0 : (approved.to_f / total * 100).round
+    }
+  end
+
   private
 
   attr_reader :window
@@ -56,8 +73,7 @@ class Captain::AssistantStatsBuilder
       handoff_rate: pack(current[:handoff], previous[:handoff], :point),
       hours_saved: pack(current[:hours_saved], previous[:hours_saved], :percent),
       reopen_rate: pack(current[:reopen], previous[:reopen], :point),
-      conversation_depth: pack(current[:depth], previous[:depth], :absolute),
-      knowledge: knowledge
+      conversation_depth: pack(current[:depth], previous[:depth], :absolute)
     }
   end
 
@@ -73,7 +89,7 @@ class Captain::AssistantStatsBuilder
       auto_resolution: rate(resolution[:resolved], handled),
       handoff: rate(resolution[:handoff], handled),
       hours_saved: (public_count * SECONDS_SAVED_PER_REPLY / 3600.0).round,
-      reopen: reopen_rate(range),
+      reopen: reopen_rate(range, resolution[:resolved]),
       depth: depth_conversations.zero? ? 0 : (public_count.to_f / depth_conversations).round(1)
     }
   end
@@ -158,7 +174,9 @@ class Captain::AssistantStatsBuilder
   # derived from the assistant's handled conversations (not current inbox membership) so a later
   # inbox reassignment doesn't drop historical resolves, and covers both the evaluated (inference)
   # and time-based (bot) resolve paths so the denominator matches auto_resolution_rate.
-  def reopen_rate(range)
+  def reopen_rate(range, resolved_count)
+    return 0 if resolved_count.zero?
+
     resolved_scope = account.reporting_events
                             .where(name: RESOLVED_EVENT_NAMES, created_at: range,
                                    conversation_id: handled_scope(range).select(:conversation_id))
@@ -178,24 +196,7 @@ class Captain::AssistantStatsBuilder
                              'ON resolves.conversation_id = reporting_events.conversation_id ' \
                              'AND reporting_events.event_end_time >= resolves.event_end_time')
                       .distinct.count('reporting_events.conversation_id')
-    rate(reopened, resolved_scope.distinct.count(:conversation_id))
-  end
-
-  # Approved/pending FAQ counts and the document total in a single round trip.
-  def knowledge
-    approved, pending, documents = Captain::AssistantResponse.by_assistant(assistant.id).reorder(nil).pick(
-      Arel.sql("COUNT(*) FILTER (WHERE status = #{Captain::AssistantResponse.statuses['approved']})"),
-      Arel.sql("COUNT(*) FILTER (WHERE status = #{Captain::AssistantResponse.statuses['pending']})"),
-      Arel.sql("(SELECT COUNT(*) FROM captain_documents WHERE assistant_id = #{assistant.id.to_i})")
-    )
-    total = approved + pending
-
-    {
-      approved: approved,
-      pending: pending,
-      documents: documents,
-      coverage: total.zero? ? 0 : (approved.to_f / total * 100).round
-    }
+    rate(reopened, resolved_count)
   end
 
   def rate(numerator, denominator)

enterprise/app/controllers/api/v1/accounts/captain/assistants_controller.rb

@@ -1,7 +1,7 @@
 class Api::V1::Accounts::Captain::AssistantsController < Api::V1::Accounts::BaseController
   before_action -> { check_authorization(Captain::Assistant) }
 
-  before_action :set_assistant, only: [:show, :update, :destroy, :playground, :stats, :summary, :drilldown]
+  before_action :set_assistant, only: [:show, :update, :destroy, :playground, :metrics, :faq_stats, :summary, :drilldown]
 
   def index
     @assistants = account_assistants.ordered
@@ -42,10 +42,14 @@ class Api::V1::Accounts::Captain::AssistantsController < Api::V1::Accounts::Base
     @tools = assistant.available_agent_tools
   end
 
-  def stats
+  def metrics
     render json: Captain::AssistantStatsBuilder.new(@assistant, params[:range], params[:timezone_offset]).metrics
   end
 
+  def faq_stats
+    render json: Captain::AssistantStatsBuilder.new(@assistant).faq_stats
+  end
+
   def summary
     window = Captain::AssistantStatsWindow.new(params[:range], params[:timezone_offset])
     result = cached_or_generated_summary(window, summary_stats)

enterprise/app/policies/captain/assistant_policy.rb

@@ -7,7 +7,11 @@ class Captain::AssistantPolicy < ApplicationPolicy
     true
   end
 
-  def stats?
+  def metrics?
+    true
+  end
+
+  def faq_stats?
     true
   end