Keep bot page totals on SQLite-maintained rooms.messages_count

X-Total-Count on GET /rooms/:id/:bot_key/messages was COUNT(*) of the
room on every page. Serve it from rooms.messages_count updated by SQLite
triggers so Rails, bulk SQL, and foreign writers stay in step — without
ActiveRecord counter_cache callbacks those paths skip.

Fixes #309.

Co-authored-by: Thomas Klemm <github@tklemm.eu>

test/controllers/messages/by_bots_controller_test.rb

@@ -1,6 +1,9 @@
 require "test_helper"
+require "active_record/testing/query_assertions"
 
 class Messages::ByBotsControllerTest < ActionDispatch::IntegrationTest
+  include ActiveRecord::Assertions::QueryAssertions
+
   setup do
     @room = rooms(:watercooler)
   end
@@ -93,11 +96,14 @@ class Messages::ByBotsControllerTest < ActionDispatch::IntegrationTest
       @room.messages.create!(body: "Filler #{i}", creator: users(:jason), client_message_id: "filler-#{i}")
     end
 
-    get room_bot_messages_url(@room, users(:bender).bot_key)
+    assert_no_queries_match(/SELECT COUNT\(\*\) FROM "messages"/i) do
+      get room_bot_messages_url(@room, users(:bender).bot_key)
+    end
     assert_response :success
 
     json = JSON.parse(response.body)
     assert_equal Message::PAGE_SIZE, json.size
+    assert_equal @room.reload.messages_count.to_s, response.headers["X-Total-Count"]
     assert_equal "41", response.headers["X-Total-Count"]
     assert_not_includes json.map { it["id"] }, messages(:fourth).id
 
@@ -119,7 +125,10 @@ class Messages::ByBotsControllerTest < ActionDispatch::IntegrationTest
   end
 
   test "index in a room with no messages" do
-    get room_bot_messages_url(rooms(:bender_and_kevin), users(:bender).bot_key)
+    room = rooms(:bender_and_kevin)
+    assert_equal 0, room.messages_count
+
+    get room_bot_messages_url(room, users(:bender).bot_key)
     assert_response :success
 
     assert_equal [], JSON.parse(response.body)