From b4ce751dcab294ede9a86aadd62acaf6e268ab4e Mon Sep 17 00:00:00 2001
From: Finn Reinhardt <f.reinhardt@basecom.de>
Date: Wed, 15 Oct 2025 16:24:05 +0200
Subject: [PATCH 1/3] Add Observer to add the Clear-Site-Data header after
 idempotent cart action

---
 Observer/AddClearSiteDataHeader.php | 32 +++++++++++++++++++++++++++++
 etc/events.xml                      | 13 ++++++++++++
 2 files changed, 45 insertions(+)
 create mode 100644 Observer/AddClearSiteDataHeader.php
 create mode 100644 etc/events.xml

diff --git a/Observer/AddClearSiteDataHeader.php b/Observer/AddClearSiteDataHeader.php
new file mode 100644
index 0000000..3e912c8
--- /dev/null
+++ b/Observer/AddClearSiteDataHeader.php
@@ -0,0 +1,32 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Basecom\Catalog\Observer;
+
+use Magento\Framework\App\Response\HttpInterface;
+use Magento\Framework\Event\Observer;
+use Magento\Framework\Event\ObserverInterface;
+
+/**
+ * Stale prefetches can be cleared using the `prefetchCache` and `prerenderCache` value of the `Clear-Site-Data response header.
+ * See [MDN documentation](https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Clear-Site-Data#prefetchcache)
+ */
+class AddClearSiteDataHeader implements ObserverInterface
+{
+    public function execute(Observer $observer): void
+    {
+        /** @var HttpInterface|null $response */
+        $response = $observer->getResponse();
+
+        if (!$response) {
+            return;
+        }
+
+        $response->setHeader(
+            'Clear-Site-Data',
+            '"prefetchCache", "prerenderCache"',
+            true
+        );
+    }
+}
diff --git a/etc/events.xml b/etc/events.xml
new file mode 100644
index 0000000..baee178
--- /dev/null
+++ b/etc/events.xml
@@ -0,0 +1,13 @@
+<?xml version="1.0"?>
+
+<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+        xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
+    <!-- Clear the prefetch & prerender cache after a product is successfully added to the cart -->
+    <event name="checkout_cart_add_product_complete">
+        <observer name="clear_site_data_header_add" instance="Basecom\Catalog\Observer\AddClearSiteDataHeader"/>
+    </event>
+    <!-- Clear the prefetch & prerender cache after a cart item is successfully -->
+    <event name="checkout_cart_update_item_complete">
+        <observer name="clear_site_data_header_update" instance="Basecom\Catalog\Observer\AddClearSiteDataHeader"/>
+    </event>
+</config>

From aa06a0211ac18a690de5ecdde787b788ff0a8a89 Mon Sep 17 00:00:00 2001
From: Finn Reinhardt <f.reinhardt@basecom.de>
Date: Wed, 15 Oct 2025 16:28:21 +0200
Subject: [PATCH 2/3] Update class path to match module

---
 Observer/AddClearSiteDataHeader.php | 2 +-
 etc/events.xml                      | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/Observer/AddClearSiteDataHeader.php b/Observer/AddClearSiteDataHeader.php
index 3e912c8..1c66d33 100644
--- a/Observer/AddClearSiteDataHeader.php
+++ b/Observer/AddClearSiteDataHeader.php
@@ -2,7 +2,7 @@
 
 declare(strict_types=1);
 
-namespace Basecom\Catalog\Observer;
+namespace MageOS\ThemeOptimization\Observer;
 
 use Magento\Framework\App\Response\HttpInterface;
 use Magento\Framework\Event\Observer;
diff --git a/etc/events.xml b/etc/events.xml
index baee178..4d2a7da 100644
--- a/etc/events.xml
+++ b/etc/events.xml
@@ -4,10 +4,10 @@
         xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
     <!-- Clear the prefetch & prerender cache after a product is successfully added to the cart -->
     <event name="checkout_cart_add_product_complete">
-        <observer name="clear_site_data_header_add" instance="Basecom\Catalog\Observer\AddClearSiteDataHeader"/>
+        <observer name="clear_site_data_header_add" instance="MageOS\ThemeOptimization\Observer\AddClearSiteDataHeader"/>
     </event>
     <!-- Clear the prefetch & prerender cache after a cart item is successfully -->
     <event name="checkout_cart_update_item_complete">
-        <observer name="clear_site_data_header_update" instance="Basecom\Catalog\Observer\AddClearSiteDataHeader"/>
+        <observer name="clear_site_data_header_update" instance="MageOS\ThemeOptimization\Observer\AddClearSiteDataHeader"/>
     </event>
 </config>

From ee0d72920e1c3fdfac697e077e189a17756bf80e Mon Sep 17 00:00:00 2001
From: Finn Reinhardt <f.reinhardt@basecom.de>
Date: Wed, 15 Oct 2025 17:09:20 +0200
Subject: [PATCH 3/3] Update comments

---
 Observer/AddClearSiteDataHeader.php | 2 +-
 etc/events.xml                      | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/Observer/AddClearSiteDataHeader.php b/Observer/AddClearSiteDataHeader.php
index 1c66d33..11897f0 100644
--- a/Observer/AddClearSiteDataHeader.php
+++ b/Observer/AddClearSiteDataHeader.php
@@ -9,7 +9,7 @@
 use Magento\Framework\Event\ObserverInterface;
 
 /**
- * Stale prefetches can be cleared using the `prefetchCache` and `prerenderCache` value of the `Clear-Site-Data response header.
+ * Stale speculative loads can be cleared using the `prefetchCache` and `prerenderCache` value of the `Clear-Site-Data` response header.
  * See [MDN documentation](https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Clear-Site-Data#prefetchcache)
  */
 class AddClearSiteDataHeader implements ObserverInterface
diff --git a/etc/events.xml b/etc/events.xml
index 4d2a7da..c88bb4a 100644
--- a/etc/events.xml
+++ b/etc/events.xml
@@ -6,7 +6,7 @@
     <event name="checkout_cart_add_product_complete">
         <observer name="clear_site_data_header_add" instance="MageOS\ThemeOptimization\Observer\AddClearSiteDataHeader"/>
     </event>
-    <!-- Clear the prefetch & prerender cache after a cart item is successfully -->
+    <!-- Clear the prefetch & prerender cache after a cart item is successfully updated -->
     <event name="checkout_cart_update_item_complete">
         <observer name="clear_site_data_header_update" instance="MageOS\ThemeOptimization\Observer\AddClearSiteDataHeader"/>
     </event>