Hand auto_link text escaped the way the serializer writes it

That's exactly what it was given before, with quotes and apostrophes
left as they are, rather than relying on its own sanitize pass to undo
h's '. Covers an email address with an apostrophe.

app/helpers/messages_helper.rb

@@ -118,13 +118,13 @@ module MessagesHelper
 
     # auto_link finds URLs and email addresses with regular expressions, which
     # can't tell an attribute value from text. Hand it one text node at a time,
-    # escaped, so a link can only land between tags.
+    # escaped as the serializer writes text, so a link can only land between tags.
     def auto_link_text(html)
       fragment = Nokogiri::HTML5.fragment(sanitize(html, tags: AUTO_LINK_ALLOWED_TAGS, attributes: AUTO_LINK_ALLOWED_ATTRIBUTES))
 
       fragment.xpath(".//text()[not(ancestor::a)]").each do |node|
         if node.text.match?(LINKABLE_TEXT)
-          text = h(node.text)
+          text = node.to_html
           linked = auto_link(text, html: { target: "_blank" })
           node.replace Nokogiri::HTML5.fragment(linked) unless linked == text
         end

test/helpers/messages_helper_test.rb

@@ -46,6 +46,13 @@ class MessagesHelperTest < ActionView::TestCase
     assert_equal [ "https://example.com/a?b=1&c=2", "me@example.com" ], links.map(&:text)
   end
 
+  test "message_presentation links an email address with an apostrophe whole" do
+    message = Message.create! room: rooms(:pets), body: "<div>Write to o'brien@example.com</div>", client_message_id: "0015", creator: users(:jason)
+
+    links = Nokogiri::HTML5.fragment(view.message_presentation(message)).css("a")
+    assert_equal [ [ "mailto:o%27brien@example.com", "o'brien@example.com" ] ], links.map { [ it["href"], it.text ] }
+  end
+
   test "message_presentation leaves URLs and email addresses in attribute values as they are" do
     [ "class", "title" ].product([ "https://example.com", "www.example.com", "me@example.com" ]).each do |attribute, linkable|
       value = "a> #{linkable} <em>b</em> "