Stop diff output from corrupting the document on structural tag changes

sdiff aligned an inserted paragraph break correctly, but the renderer
wrapped the raw </p>/<p> tokens in <ins> regardless -- invalid nesting
that browsers silently repair by dropping the unmatched closing tag,
leaving everything downstream rendered inside an <ins> with nothing
left to close it. Same failure mode as the retired cacycle_diff.js,
different cause.

Tag tokens now render as a plain-text pilcrow with a tooltip naming
the actual tag, never as literal markup inside <ins>/<del>. Applies to
both inline and side-by-side. Side-by-side's new panel flattening a
real paragraph break into a marker, rather than showing its own true
structure, is a known, accepted trade-off for now -- not the same
problem, and not fixed here.

1 files changed, 18 insertions, 0 deletions

diff --git a/test/models/page_test.rb b/test/models/page_test.rb
index ac5691a..3868a53 100644
--- a/test/models/page_test.rb
+++ b/test/models/page_test.rb
@@ -210,4 +210,22 @@ class PageTest < ActiveSupport::TestCase
     assert_match "<del>Old</del>", old_html
     assert_match "<ins>New</ins>", new_html
   end
+
+  test "diff_against handles an inserted paragraph split without corrupting the document" do
+    n = Node.root.children.create! :slug => "paragraph_split_test"
+    d = n.find_or_create_draft @user1
+    d.body = "<p>Der Vortragsraum ist ab 19 Uhr geöffnet, der Zugang erfolgt über den Hinterhof.</p>"
+    d.save!
+    n.publish_draft!
+
+    d2 = n.find_or_create_draft @user1
+    d2.body = "<p>Der Vortragsraum ist ab 19 Uhr geöffnet,</p>\n<p>der Zugang erfolgt über den Hinterhof.</p>"
+    d2.save!
+
+    diff = d2.diff_against(n.head)
+    fragment = Nokogiri::HTML::DocumentFragment.parse(diff[:body])
+
+    assert_equal 2, fragment.css('ins.diff_structural').length
+    assert_match "der Zugang erfolgt über den Hinterhof.", fragment.text
+  end
 end