diff --git a/CLAUDE.md b/CLAUDE.md
index 5c59252..4a55bcf 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -299,7 +299,10 @@ passes.
   swatch block's cache key calls before the block cache, so it is paid on
   every render; the lowest price options provider picks the cheapest child by
   final and by regular price from `priceIndex` (per-variant discounts make
-  those different children) and wraps core's provider for the rest. A child's
+  those different children) and wraps core's provider for the rest;
+  `getParentIdsByChild()` answers from the `parentIds` of the page's card and
+  variant documents, which core's identities plugin asks for every simple
+  product a card tags, a query each on every render. A child's
   `entity_id` and a super attribute's `position` are strings, since
   `getJsonConfig()` puts them into the rendered JSON as they are. Without
   the `configurableOptions` field the plugin hands over to core with nothing logged.
diff --git a/src/CatalogStorefrontConfigurableProductFrontend/Plugin/Listing/ParentIdsFromDocuments.php b/src/CatalogStorefrontConfigurableProductFrontend/Plugin/Listing/ParentIdsFromDocuments.php
new file mode 100644
index 0000000..1d68645
--- /dev/null
+++ b/src/CatalogStorefrontConfigurableProductFrontend/Plugin/Listing/ParentIdsFromDocuments.php
@@ -0,0 +1,61 @@
+<?php
+declare(strict_types=1);
+
+namespace GraphCommerce\CatalogStorefrontConfigurableProductFrontend\Plugin\Listing;
+
+use GraphCommerce\CatalogStorefrontConfigurableProductFrontend\Model\Read\VariantDocuments;
+use GraphCommerce\CatalogStorefrontProductFrontend\Model\Read\ListingDocuments;
+use Magento\ConfigurableProduct\Model\Product\Type\Configurable;
+use Magento\Store\Model\StoreManagerInterface;
+
+/**
+ * Answers the configurable parents of a card product, or of a variant of a card, from its
+ * document. Core's identities plugin asks them for every simple product whose identities a card
+ * collects, a query per product on every render, also when the card's block cache hits. A product
+ * whose document the page did not read goes to core.
+ */
+class ParentIdsFromDocuments
+{
+    public function __construct(
+        private readonly ListingDocuments $page,
+        private readonly VariantDocuments $variants,
+        private readonly StoreManagerInterface $storeManager,
+    ) {
+    }
+
+    /**
+     * @param Configurable $subject
+     * @param \Closure $proceed
+     * @param int|string|int[]|string[] $childId
+     * @return string[]
+     * @SuppressWarnings(PHPMD.UnusedFormalParameter)
+     */
+    public function aroundGetParentIdsByChild(Configurable $subject, \Closure $proceed, $childId)
+    {
+        $store = $this->storeManager->getStore();
+        $cards = $this->page->documents((string)$store->getCode());
+        if ($cards === []) {
+            return $proceed($childId);
+        }
+
+        $ids = array_map('intval', (array)$childId);
+        $documents = array_intersect_key($cards, array_flip($ids));
+        $rest = array_values(array_diff($ids, array_keys($documents)));
+        if ($rest !== []) {
+            $variants = $this->variants->documents($store, $rest);
+            if ($variants === null || count($variants) !== count($rest)) {
+                return $proceed($childId);
+            }
+            $documents += $variants;
+        }
+
+        $parentIds = [];
+        foreach ($documents as $document) {
+            foreach ((array)($document['parentIds'] ?? []) as $parentId) {
+                $parentIds[(string)$parentId] = (string)$parentId;
+            }
+        }
+
+        return array_values($parentIds);
+    }
+}
diff --git a/src/CatalogStorefrontConfigurableProductFrontend/README.md b/src/CatalogStorefrontConfigurableProductFrontend/README.md
index 0f09a01..dd3f467 100644
--- a/src/CatalogStorefrontConfigurableProductFrontend/README.md
+++ b/src/CatalogStorefrontConfigurableProductFrontend/README.md
@@ -15,5 +15,8 @@ GraphCommerce_CatalogStorefrontProductFrontend.
   the page's child price ranges, so the card prices without its variant documents. A product
   detail page, a store with fixed product taxes and a product without a range pick the
   cheapest child by final price and by regular price from `priceIndex`.
+- `getParentIdsByChild()` answers from the `parentIds` of a card's document or of a card
+  variant's document. Core's identities plugin asks it for every simple product whose cache
+  tags a card collects, a query per product on every render, also on a block cache hit.
 
 Each seam hands a product without a document to core.
diff --git a/src/CatalogStorefrontConfigurableProductFrontend/Test/Unit/Plugin/Listing/ParentIdsFromDocumentsTest.php b/src/CatalogStorefrontConfigurableProductFrontend/Test/Unit/Plugin/Listing/ParentIdsFromDocumentsTest.php
new file mode 100644
index 0000000..7a2e9da
--- /dev/null
+++ b/src/CatalogStorefrontConfigurableProductFrontend/Test/Unit/Plugin/Listing/ParentIdsFromDocumentsTest.php
@@ -0,0 +1,124 @@
+<?php
+declare(strict_types=1);
+
+namespace GraphCommerce\CatalogStorefrontConfigurableProductFrontend\Test\Unit\Plugin\Listing;
+
+use GraphCommerce\CatalogStorefrontConfigurableProductFrontend\Model\Read\VariantDocuments;
+use GraphCommerce\CatalogStorefrontConfigurableProductFrontend\Plugin\Listing\ParentIdsFromDocuments;
+use GraphCommerce\CatalogStorefrontProductFrontend\Model\Read\ListingDocuments;
+use Magento\ConfigurableProduct\Model\Product\Type\Configurable;
+use Magento\Store\Api\Data\StoreInterface;
+use Magento\Store\Model\StoreManagerInterface;
+use PHPUnit\Framework\TestCase;
+
+class ParentIdsFromDocumentsTest extends TestCase
+{
+    private int $coreCalls = 0;
+
+    /** @var int[][] the child ids each variant read asked for */
+    private array $variantReads = [];
+
+    /**
+     * @param array<int, array>|null $variants what the variant read answers
+     */
+    private function plugin(ListingDocuments $page, ?array $variants = null): ParentIdsFromDocuments
+    {
+        $store = $this->createMock(StoreInterface::class);
+        $store->method('getCode')->willReturn('default');
+        $storeManager = $this->createMock(StoreManagerInterface::class);
+        $storeManager->method('getStore')->willReturn($store);
+
+        $variantDocuments = $this->createMock(VariantDocuments::class);
+        $variantDocuments->method('documents')->willReturnCallback(
+            function ($store, array $childIds) use ($variants): ?array {
+                $this->variantReads[] = $childIds;
+
+                return $variants === null ? null : array_intersect_key($variants, array_flip($childIds));
+            }
+        );
+
+        return new ParentIdsFromDocuments($page, $variantDocuments, $storeManager);
+    }
+
+    private function page(array $documents, string $storeViewCode = 'default'): ListingDocuments
+    {
+        $page = new ListingDocuments();
+        $page->add($storeViewCode, $documents);
+
+        return $page;
+    }
+
+    private function call(ParentIdsFromDocuments $plugin, $childId): array
+    {
+        return $plugin->aroundGetParentIdsByChild(
+            $this->createMock(Configurable::class),
+            function () {
+                $this->coreCalls++;
+
+                return ['core'];
+            },
+            $childId
+        );
+    }
+
+    public function testCardAnswersFromItsDocument(): void
+    {
+        $plugin = $this->plugin($this->page([10 => ['parentIds' => [7, 8]]]));
+
+        $this->assertSame(['7', '8'], $this->call($plugin, '10'));
+        $this->assertSame([], $this->variantReads);
+        $this->assertSame(0, $this->coreCalls);
+    }
+
+    public function testCardWithoutParentsAnswersEmpty(): void
+    {
+        $plugin = $this->plugin($this->page([10 => ['sku' => 'simple']]));
+
+        $this->assertSame([], $this->call($plugin, 10));
+        $this->assertSame(0, $this->coreCalls);
+    }
+
+    public function testVariantOfACardAnswersFromTheVariantDocuments(): void
+    {
+        $plugin = $this->plugin($this->page([7 => ['variantIds' => [21]]]), [21 => ['parentIds' => [7]]]);
+
+        $this->assertSame(['7'], $this->call($plugin, 21));
+        $this->assertSame([[21]], $this->variantReads);
+        $this->assertSame(0, $this->coreCalls);
+    }
+
+    public function testSeveralProductsMergeTheirParentsOnce(): void
+    {
+        $plugin = $this->plugin(
+            $this->page([10 => ['parentIds' => [7]]]),
+            [21 => ['parentIds' => [7, 9]]]
+        );
+
+        $this->assertSame(['7', '9'], $this->call($plugin, [10, 21]));
+        $this->assertSame([[21]], $this->variantReads);
+    }
+
+    public function testProductWithoutADocumentGoesToCore(): void
+    {
+        $plugin = $this->plugin($this->page([10 => ['parentIds' => [7]]]), [21 => ['parentIds' => [7]]]);
+
+        $this->assertSame(['core'], $this->call($plugin, [10, 22]));
+        $this->assertSame(1, $this->coreCalls);
+    }
+
+    public function testVariantReadThatCoversNothingGoesToCore(): void
+    {
+        $plugin = $this->plugin($this->page([7 => ['variantIds' => [21]]]));
+
+        $this->assertSame(['core'], $this->call($plugin, 21));
+        $this->assertSame(1, $this->coreCalls);
+    }
+
+    public function testRequestWithoutListingDocumentsGoesToCore(): void
+    {
+        $this->assertSame(['core'], $this->call($this->plugin(new ListingDocuments()), 10));
+        $this->assertSame(['core'], $this->call($this->plugin($this->page([10 => []], 'other')), 10));
+        $this->assertSame(2, $this->coreCalls);
+        $this->assertSame([], $this->variantReads);
+    }
+}
diff --git a/src/CatalogStorefrontConfigurableProductFrontend/etc/di.xml b/src/CatalogStorefrontConfigurableProductFrontend/etc/di.xml
index 37068f9..41913a1 100644
--- a/src/CatalogStorefrontConfigurableProductFrontend/etc/di.xml
+++ b/src/CatalogStorefrontConfigurableProductFrontend/etc/di.xml
@@ -1,11 +1,13 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
-    <!-- Both act only on a product that carries a document, so a core-served page is untouched. -->
+    <!-- They act only on a product that carries a document, so a core-served page is untouched. -->
     <type name="Magento\ConfigurableProduct\Model\Product\Type\Configurable">
         <plugin name="graphcommerce_catalog_storefront_used_products"
                 type="GraphCommerce\CatalogStorefrontConfigurableProductFrontend\Plugin\Listing\UsedProductsFromDocuments"/>
         <plugin name="graphcommerce_catalog_storefront_configurable_attributes"
                 type="GraphCommerce\CatalogStorefrontConfigurableProductFrontend\Plugin\Listing\ConfigurableAttributesFromDocument"/>
+        <plugin name="graphcommerce_catalog_storefront_parent_ids"
+                type="GraphCommerce\CatalogStorefrontConfigurableProductFrontend\Plugin\Listing\ParentIdsFromDocuments"/>
     </type>
 
     <!-- The swatch renderer of a document product renders without the block cache. -->