Magento Customer Segment: keep segment IDs out of the full page cache key
=========================================================================

Package:  magento/module-customer-segment (tested on 102.1.8-p3)
Author:   Paxento, https://paxento.com/
Article:  https://paxento.com/magento-customer-segments-full-page-cache/
License:  provided as-is, without warranty. Test on staging before production.

Adds a plugin that removes the customer segment value from the HTTP context, so
logged-in customers in different segments share cached pages again.
Only safe if no cached page content is targeted by segment.

Apply with cweagans/composer-patches or vaimo/composer-patches, e.g.:
  "patches": {
    "magento/module-customer-segment": {
      "Keep segments out of the page cache key": "patches/magento-customer-segment-keep-segments-out-of-page-cache.patch"
    }
  }

diff --git a/Model/App/Http/ContextPlugin.php b/Model/App/Http/ContextPlugin.php
new file mode 100644
index 0000000..d91ed50
--- /dev/null
+++ b/Model/App/Http/ContextPlugin.php
@@ -0,0 +1,29 @@
+<?php
+
+namespace Magento\CustomerSegment\Model\App\Http;
+
+use Magento\CustomerSegment\Helper\Data;
+use Magento\Framework\App\Http\Context as Subject;
+
+class ContextPlugin
+{
+    /**
+     * Unset customer segment ids from HTTP context
+     *
+     * @param Subject $httpContext
+     * @param Subject $result
+     * @param string $name
+     * @return Subject
+     */
+    public function afterSetValue(
+        Subject $httpContext,
+        Subject $result,
+        string $name
+    ): Subject {
+        if (Data::CONTEXT_SEGMENT === $name) {
+            $httpContext->unsValue($name);
+        }
+
+        return $result;
+    }
+}
diff --git a/etc/frontend/di.xml b/etc/frontend/di.xml
index 5b4794e..ec64bde 100644
--- a/etc/frontend/di.xml
+++ b/etc/frontend/di.xml
@@ -14,6 +14,10 @@
         <plugin name="customer-segment-app-action-dispatchController-context-plugin"
                 type="Magento\CustomerSegment\Model\App\Action\ContextPlugin" sortOrder="10"/>
     </type>
+    <type name="Magento\Framework\App\Http\Context">
+        <plugin name="customer-segment-app-http-context-plugin"
+                type="Magento\CustomerSegment\Model\App\Http\ContextPlugin" sortOrder="10"/>
+    </type>
     <type name="Magento\Checkout\Model\Cart\CollectQuote">
         <plugin name="checkout_cart_collect_totals" type="Magento\CustomerSegment\Model\Checkout\Block\Cart\Shipping\Plugin"/>
     </type>