Ensure backwards compatibility with Trix

test/system/composer_test.rb

@@ -68,6 +68,24 @@ class ComposerTest < ApplicationSystemTestCase
     assert_equal [ users(:jason) ], message.reload.mentionees
   end
 
+  test "editing a legacy trix message keeps its mention and embed" do
+    body = %(<div>Hey #{mention_attachment_for(:jason)} check <action-text-attachment content-type="application/vnd.actiontext.opengraph-embed" url="https://example.com/image.png" href="https://example.com/" filename="Example title" caption="Example description"></action-text-attachment></div>)
+    message = Message.create! room: rooms(:designers), body: body, client_message_id: "legacy", creator: users(:jz)
+
+    join_room rooms(:designers)
+
+    within_message message do
+      reveal_message_actions
+      find(".message__edit-btn").click
+      assert_edit_editor_text "Jason"
+      click_on "Save changes"
+    end
+
+    assert_selector last_message_selector(".mention"), text: "Jason"
+    assert_selector last_message_selector(%(.og-embed__title a[href="https://example.com/"])), text: "Example title"
+    assert_equal [ users(:jason) ], message.reload.mentionees
+  end
+
   test "replying quotes the original message with attribution" do
     within_message messages(:third) do
       reveal_message_actions