The reason 640 collapsed lists shipped green is that no test exercised real
markdown->HTML rendering — the existing build_html_reader tests stub pandoc with
a fake, covering TOC/mermaid plumbing but never the markdown parse. This feeds
the exact bold-lead-in pattern through the real pandoc invocation the reader uses
and asserts the list survives as <ul>. Proven both ways: passes with the
extension, fails when it is removed.
