diff --git a/third_party/blink/renderer/core/frame/web_frame_widget_impl.cc b/third_party/blink/renderer/core/frame/web_frame_widget_impl.cc
index 439b3b533363d..e4800402ffc3a 100644
--- a/third_party/blink/renderer/core/frame/web_frame_widget_impl.cc
+++ b/third_party/blink/renderer/core/frame/web_frame_widget_impl.cc
@@ -36,6 +36,8 @@
 #include "base/auto_reset.h"
 #include "base/containers/to_vector.h"
 #include "base/debug/crash_logging.h"
+#include "base/threading/platform_thread.h"
+#include "third_party/blink/renderer/platform/loader/fetch/loader_freeze_mode.h"
 #include "base/debug/dump_without_crashing.h"
 #include "base/functional/callback_helpers.h"
 #include "base/functional/function_ref.h"
@@ -2614,7 +2616,18 @@ void WebFrameWidgetImpl::Resize(const gfx::Size& new_size) {
 
   if (child_data().did_suspend_parsing) {
     child_data().did_suspend_parsing = false;
-    LocalRootImpl()->GetFrame()->Loader().GetDocumentLoader()->ResumeParser();
+    // POC: ensure at least one body segment is buffered in
+    // DocumentLoader::data_buffer_ before ResumeParser enters the range-for.
+    // Sleep so the network process has written body bytes into the Mojo data
+    // pipe, then toggle freeze mode (kStrict -> kNone) which is exactly what
+    // ScopedPagePauser ctor/dtor do; the kNone transition synchronously calls
+    // NavigationBodyLoader::OnReadable -> ProcessDataBuffer -> Append while
+    // parser_blocked_count_ > 0.
+    auto* dl = LocalRootImpl()->GetFrame()->Loader().GetDocumentLoader();
+    base::PlatformThread::Sleep(base::Milliseconds(300));
+    dl->SetDefersLoading(blink::LoaderFreezeMode::kStrict);
+    dl->SetDefersLoading(blink::LoaderFreezeMode::kNone);
+    dl->ResumeParser();
   }
 
   LocalFrameView* view = LocalRootImpl()->GetFrameView();
@@ -5408,7 +5421,13 @@ void WebFrameWidgetImpl::DidCreateLocalRootView() {
   // If this WebWidget still hasn't received its size from the embedder, block
   // the parser. This is necessary, because the parser can cause layout to
   // happen, which needs to be done with the correct size.
-  if (ForSubframe() && !size_) {
+  // POC: force the BlockParser path. In production this happens when the
+  // CommitNavigation IPC for a fresh OOPIF local root beats the first
+  // UpdateVisualProperties IPC; we make it deterministic by also resetting
+  // size_ so the next Resize() call (which the browser sends on parent
+  // layout) takes the did_suspend_parsing -> ResumeParser branch.
+  if (ForSubframe()) {
+    size_.reset();
     child_data().did_suspend_parsing = true;
     LocalRootImpl()->GetFrame()->Loader().GetDocumentLoader()->BlockParser();
   }
diff --git a/third_party/blink/renderer/core/page/chrome_client.cc b/third_party/blink/renderer/core/page/chrome_client.cc
index 9f6bd185cd318..691a6f9b4d7e3 100644
--- a/third_party/blink/renderer/core/page/chrome_client.cc
+++ b/third_party/blink/renderer/core/page/chrome_client.cc
@@ -23,6 +23,7 @@
 
 #include <algorithm>
 
+#include "base/threading/platform_thread.h"
 #include "third_party/blink/public/platform/platform.h"
 #include "third_party/blink/public/platform/web_prescient_networking.h"
 #include "third_party/blink/renderer/core/core_initializer.h"
@@ -100,8 +101,17 @@ static bool OpenJavaScriptDialog(LocalFrame* frame,
   // otherwise cause the load to continue while we're in the middle of
   // executing JavaScript.
   ScopedPagePauser pauser;
+  // POC: widen the per-alert window so the network process has time to write
+  // another body chunk into the navigation Mojo data pipe before |pauser|'s
+  // destructor calls SetDefersLoading(kNone) -> OnReadable -> Append.
+  base::PlatformThread::Sleep(base::Milliseconds(30));
   probe::WillRunJavaScriptDialog(frame);
-  bool result = delegate();
+  // POC: skip the sync RunModalAlertDialog Mojo IPC so headless runs without
+  // a dialog manager. In production the cross-origin-iframe alert is
+  // suppressed browser-side and the sync call returns immediately; the
+  // ScopedPagePauser ctor/dtor sequence (the relevant part) is unchanged.
+  bool result = true;
+  (void)delegate;
   probe::DidRunJavaScriptDialog(frame);
   return result;
 }