A document can forge both a console message and its source (KaTeX's \errmessage, data: scripts, sourceURL, encoded paths), so the display handler logs a line number and nothing the page wrote. The page's own diagnostics reach the app over elyQuery: a missed reveal sends its line; the visual failure and diagram lines already did. A test calls the real handler and checks the captured log. Round 5 found only the missing test; it is added and mutation-checked, with no sixth review under the five-round cap. M-15 is new: the print page runs a document's scripts. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>