The preview showed the page's thumbnail, old marks and all, until the
unmarked page rendered, and one page that failed to render switched the
unmarked preview off for every page. The page shown is now drawn from the
unmarked document straight away at the preview's size; the pages a step
goes to render ahead off the UI thread; a page that fails falls back to
its own thumbnail while the others keep theirs.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>