Fix missing partial when editing comments with @mentions (#2828)

Edge Rails introduced ActionText::Attachable#to_editor_content_attachment_partial_path
which defaults to to_partial_path ("users/user"). Override it in User::Mentionable to
delegate to to_attachable_partial_path ("users/attachable"), matching the existing
display rendering path.

app/models/user/mentionable.rb

@@ -8,6 +8,10 @@ module User::Mentionable
     def to_attachable_partial_path
       "users/attachable"
     end
+
+    def to_editor_content_attachment_partial_path
+      to_attachable_partial_path
+    end
   end
 
   def mentioned_by(mentioner, at:)

test/controllers/cards/comments_controller_test.rb

@@ -113,6 +113,22 @@ class Cards::CommentsControllerTest < ActionDispatch::IntegrationTest
     assert_equal "Updated comment", comment.reload.body.to_plain_text
   end
 
+  test "edit a comment that contains a mention" do
+    card = cards(:logo)
+    mentioned_user = users(:jz)
+    mention_html = ActionText::Attachment.from_attachable(mentioned_user).to_html
+    comment = card.comments.create!(creator: users(:kevin), body: "#{mention_html} hello")
+
+    get edit_card_comment_path(card, comment)
+    assert_response :success
+    assert_select "lexxy-editor" do |editors|
+      value = editors.first["value"]
+      attachment = Nokogiri::HTML.fragment(value).at_css("action-text-attachment")
+      assert_equal mentioned_user.attachable_sgid, attachment["sgid"]
+      assert_includes attachment["content"], mentioned_user.first_name
+    end
+  end
+
   test "destroy as JSON" do
     comment = comments(:logo_agreement_kevin)