diff --git a/static/ui.js b/static/ui.js
index adff96c9..fd444e65 100644
--- a/static/ui.js
+++ b/static/ui.js
@@ -16640,7 +16640,8 @@ function _processWakeupCardHtml(info, rawText, extras){
 
 function renderMessages(options){
   _lastMessageRenderAt=performance.now();
-  if(!(options&&options._internalMeasurement)){ _resetMessageVirtualMeasurementBurst(); }
+  // typeof guard: node harnesses extract renderMessages() without its helpers (#6717).
+  if(!(options&&options._internalMeasurement) && typeof _resetMessageVirtualMeasurementBurst==='function'){ _resetMessageVirtualMeasurementBurst(); }
   const preserveScroll=!!(options&&options.preserveScroll);
   const virtualFallback=!!(options&&options._virtualFallback);
   // Capture the pre-wipe scroll position when preserving OR when the reader has
diff --git a/tests/test_issue4346_vscroll_footer_jitter.py b/tests/test_issue4346_vscroll_footer_jitter.py
index 12d14185..5448a907 100644
--- a/tests/test_issue4346_vscroll_footer_jitter.py
+++ b/tests/test_issue4346_vscroll_footer_jitter.py
@@ -99,7 +99,7 @@ def test_js_recycle_flag_lifecycle():
     """_scheduleMessageVirtualizedRender sets _msgNodeRecycleEnabled=true
     before the compensate call and clears it in finally."""
     fn_match = re.search(
-        r'function _scheduleMessageVirtualizedRender\(force\)\{(.+?)^(?=function )',
+        r'function _scheduleMessageVirtualizedRender\(force(?:, request)?\)\{(.+?)^(?=function )',
         JS, re.DOTALL | re.MULTILINE
     )
     assert fn_match, "_scheduleMessageVirtualizedRender not found"
@@ -1101,7 +1101,7 @@ class TestScrollbarDragRenderDuringDrag:
         """_scheduleMessageVirtualizedRender must have a _scrollbarDragActive
         branch that runs a full render with scroll compensation."""
         fn_match = re.search(
-            r'function _scheduleMessageVirtualizedRender\(force\)\{(.+?)^(?=function )',
+            r'function _scheduleMessageVirtualizedRender\(force(?:, request)?\)\{(.+?)^(?=function )',
             JS, re.DOTALL | re.MULTILINE
         )
         assert fn_match, "_scheduleMessageVirtualizedRender not found"