Preload only uncached messages and reduce rendering overhead (#292)

* Preload only uncached messages and reduce rendering overhead

* Keep benchmark summaries without raw JSON results

* Use Ruby benchmark drivers and keep generated results out of the repo

test/models/message_test.rb

@@ -1,7 +1,8 @@
 require "test_helper"
+require "active_record/testing/query_assertions"
 
 class MessageTest < ActiveSupport::TestCase
-  include ActionCable::TestHelper, ActiveJob::TestHelper
+  include ActionCable::TestHelper, ActiveJob::TestHelper, ActiveRecord::Assertions::QueryAssertions
 
   test "creating a message enqueues to push later" do
     assert_enqueued_jobs 1, only: [ Room::PushMessageJob ] do
@@ -27,6 +28,43 @@ class MessageTest < ActiveSupport::TestCase
     assert_equal [], message_mentioning_a_non_member.mentionees
   end
 
+  test "presentation associations load together" do
+    messages(:first).attachment.attach io: StringIO.new("hello"), filename: "hello.txt", content_type: "text/plain"
+    presented = Message.where(id: [ messages(:first).id, messages(:thirteenth).id ]).with_presentation.to_a
+
+    assert_no_queries do
+      presented.each do |message|
+        message.room.name
+        message.creator.avatar.attached?
+        message.body.body.to_html
+        message.body.embeds.each(&:filename)
+        message.attachment.blob&.filename
+        message.boosts.each { |boost| boost.booster.avatar.attached? }
+      end
+    end
+  end
+
+  test "presentation pages preload only the rendered messages" do
+    page = rooms(:watercooler).messages.with_presentation.last_page
+    assert_kind_of Array, page
+    assert page.all? { |message| !message.association(:rich_text_body).loaded? }
+
+    rendered = page.first(2)
+    page.preload_associations(rendered)
+
+    assert_no_queries { rendered.each { |message| message.body.to_plain_text } }
+    assert page.drop(2).all? { |message| !message.association(:rich_text_body).loaded? }
+  end
+
+  test "pagination retains the original ordering even when timestamps tie" do
+    room = rooms(:watercooler)
+    room.messages.update_all(created_at: Time.current)
+    expected = room.messages.ordered.last(Message::Pagination::PAGE_SIZE).map(&:id)
+
+    assert_equal expected, room.messages.last_page.map(&:id)
+    assert_equal room.messages.ordered.first(Message::Pagination::PAGE_SIZE).map(&:id), room.messages.first_page.map(&:id)
+  end
+
   private
     def create_new_message_in(room)
       room.messages.create!(creator: users(:jason), body: "Hello", client_message_id: "123")