Rendering
The blank sheet passes every check that looks at the file.
The expensive failure in document generation is not a crash. A crash is loud, it has a stack trace, and somebody fixes it that afternoon. The expensive failure is a sheet that renders successfully and carries nothing: correct title block, correct sheet number, correct paper size, correct file extension, and an empty drawing area.
It opens. It prints. It has a plausible byte count. It passes every check written against the artifact rather than against the drawing — which is most of them, because checking a file is easy and checking a drawing is not.
So the blank sheet has its own regression class in this engine, separate from the rest of the suite. Not a note in a checklist, not a code review habit: a named class of test that fails on emptiness specifically. It exists because the failure recurred, and because a rule that lives only in somebody’s memory is a rule that has already been skipped once.
The wider version of the lesson is unglamorous. When a system can fail silently, the check has to be aimed at the silence, not at the surface it hides behind.