The isolated-line density guard wiped every isolated line on a page
where they exceeded 25% of lines. On sparse pages (covers, ToC pages
with a lone "CONTENTS" title, section-divider pages) a single heading
is trivially >25%, so the guard erased exactly the line it exists to
find. Require the page to have >=10 lines before the guard runs — the
25% ratio only signals a multi-column misfire on a dense page.
That let more isolated lines through, exposing that the visual heading
heuristic could promote lines already tagged with a non-heading struct
role (list item, blockquote, code, caption, ToC) or set in a monospace
font. Gate the heuristic on those in both converter paths.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
