_scheduleMessageVirtualizedRender now takes (force, request), so the two
structural probes in test_issue4346_vscroll_footer_jitter.py matched nothing.
renderMessages() calls _resetMessageVirtualMeasurementBurst(), which node
harnesses that extract renderMessages() alone (test_compaction_current_summary_fallback.py)
don't define; guard it with typeof like the file's other optional helpers.