perf(conversations): optimize /conversations/meta with counter cache for all_count

app/finders/conversation_finder.rb

@@ -170,7 +170,7 @@ class ConversationFinder
     [
       @conversations.assigned_to(current_user).count,
       @conversations.unassigned.count,
-      @conversations.count
+      current_account.conversations_count
     ]
   end
 

app/models/conversation.rb

@@ -97,7 +97,7 @@ class Conversation < ApplicationRecord
     ).sort_on_last_user_message_at
   }
 
-  belongs_to :account
+  belongs_to :account, counter_cache: true
   belongs_to :inbox
   belongs_to :assignee, class_name: 'User', optional: true, inverse_of: :assigned_conversations
   belongs_to :assignee_agent_bot, class_name: 'AgentBot', optional: true

db/migrate/20260203062506_add_conversations_count_to_accounts.rb

@@ -0,0 +1,5 @@
+class AddConversationsCountToAccounts < ActiveRecord::Migration[7.1]
+  def change
+    add_column :accounts, :conversations_count, :integer, default: 0, null: false
+  end
+end

db/migrate/20260203062518_backfill_conversations_count.rb

@@ -0,0 +1,11 @@
+class BackfillConversationsCount < ActiveRecord::Migration[7.1]
+  def up
+    Account.find_each do |account|
+      Account.reset_counters(account.id, :conversations)
+    end
+  end
+
+  def down
+    # No-op
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.1].define(version: 2026_01_30_061021) do
+ActiveRecord::Schema[7.1].define(version: 2026_02_03_062518) do
   # These extensions should be enabled to support this database
   enable_extension "pg_stat_statements"
   enable_extension "pg_trgm"
@@ -73,6 +73,7 @@ ActiveRecord::Schema[7.1].define(version: 2026_01_30_061021) do
     t.integer "status", default: 0
     t.jsonb "internal_attributes", default: {}, null: false
     t.jsonb "settings", default: {}
+    t.integer "conversations_count", default: 0, null: false
     t.index ["status"], name: "index_accounts_on_status"
   end