diff --git a/php-transformer/composer.json b/php-transformer/composer.json
index 93375ebe9..0051bd6d9 100644
--- a/php-transformer/composer.json
+++ b/php-transformer/composer.json
@@ -348,6 +348,7 @@
       "php tests/unit/captured-dialog-open-state.php",
       "php tests/unit/captured-dialog-dropdown-panel.php",
       "php tests/unit/captured-dialog-shared-header.php",
+      "php tests/unit/captured-dialog-ordinal-shared-header.php",
       "php tests/unit/captured-dialog-editor-at-rest.php",
       "php tests/unit/scoped-mixed-dropdown.php",
       "php tests/unit/capture-runtime-ancestor-parity.php",
diff --git a/php-transformer/src/WordPressSitePlan/ShellExtraction.php b/php-transformer/src/WordPressSitePlan/ShellExtraction.php
index d56cd43ee..cf55227e8 100644
--- a/php-transformer/src/WordPressSitePlan/ShellExtraction.php
+++ b/php-transformer/src/WordPressSitePlan/ShellExtraction.php
@@ -2708,7 +2708,9 @@ private static function normalizeNestedChromeMarkup(string $markup): string
         $markup = self::withoutScrollStateCarrierIdentity($markup);
         $markup = preg_replace('/\s*' . EngineMarker::patternBody() . '/', '', $markup) ?? $markup;
         $markup = preg_replace('/\s*(?:' . EngineMarker::specificityPatternBody('specificity-class') . '|blocks-engine-disclosure-summary-[a-f0-9]{6,}(?:-\d+)?)/', '', $markup) ?? $markup;
-        // A captured dialog's generated id, and its triggers' ids, carry a per-document hash.
+        // A captured dialog's generated id, and its triggers' ids, carry a per-document hash;
+        // the capture's own panel handle (id, panel attribute, aria-controls) carries a per-document ordinal.
+        $markup = preg_replace('/\b' . preg_quote(CaptureEvidence::DIALOG_CLASS, '/') . '-\d+\b/', CaptureEvidence::DIALOG_CLASS, $markup) ?? $markup;
         $markup = preg_replace('/blocks-engine-dialog-trigger-[a-f0-9]+-(\d+)/', 'blocks-engine-dialog-trigger-$1', $markup) ?? $markup;
         $markup = preg_replace('/blocks-engine-dialog-[a-f0-9]{16}\b/', 'blocks-engine-dialog', $markup) ?? $markup;
         $markup = preg_replace('/\s*be-inline-geometry-[a-f0-9]{16}(?:-[a-f0-9]{16})?/', '', $markup) ?? $markup;
diff --git a/php-transformer/tests/unit/captured-dialog-ordinal-shared-header.php b/php-transformer/tests/unit/captured-dialog-ordinal-shared-header.php
new file mode 100644
index 000000000..f96532266
--- /dev/null
+++ b/php-transformer/tests/unit/captured-dialog-ordinal-shared-header.php
@@ -0,0 +1,68 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * A header whose captured dialog panel id is an ordinal is still shared chrome.
+ *
+ * The capture numbers dialog panels per route (`data-blocks-engine-capture-dialog-N`),
+ * so identical headers carry different ordinals in the panel id, its panel
+ * handle, and the trigger's aria-controls. Shell identity must ignore that
+ * ordinal, while headers whose dialogs differ in content stay unshared.
+ */
+
+require dirname(__DIR__, 2) . '/vendor/autoload.php';
+
+use Automattic\BlocksEngine\PhpTransformer\ArtifactCompiler\ArtifactCompiler;
+
+$failures = 0;
+$passes = 0;
+$assert = static function (bool $ok, string $message, string $detail = '') use (&$failures, &$passes): void {
+    if ($ok) {
+        ++$passes;
+        return;
+    }
+    ++$failures;
+    fwrite(STDERR, 'FAIL: ' . $message . ('' !== $detail ? ' - ' . substr($detail, 0, 600) : '') . PHP_EOL);
+};
+
+$links = '<ul><li><a href="/">Home</a></li><li><a href="/about.html">About</a></li><li><a href="/contact.html">Contact</a></li></ul>';
+$header = static fn(int $n, string $dialogLinks): string => '<header><a href="/">Acme</a><nav aria-label="Site">' . $links . '</nav>' . "\n"
+    . '<button type="button" class="menu-btn" aria-expanded="false" aria-haspopup="dialog" aria-label="Menu" aria-controls="data-blocks-engine-capture-dialog-' . $n . '">☰</button>' . "\n"
+    . '<div class="data-blocks-engine-capture-dialog" role="dialog" aria-modal="true" hidden id="data-blocks-engine-capture-dialog-' . $n . '" data-blocks-engine-capture-dialog-panel="data-blocks-engine-capture-dialog-' . $n . '" aria-label="Site navigation">' . $dialogLinks . '</div></header>';
+
+$compile = static function (callable $dialogFor) use ($header): array {
+    $files = array();
+    foreach (array('index.html' => 'Home', 'about.html' => 'About', 'contact.html' => 'Contact') as $path => $title) {
+        $n = count($files);
+        $files[] = array('path' => $path, 'content' => '<!doctype html><html><head><title>' . $title . '</title></head><body>' . $header($n, $dialogFor($n)) . '<main><h1>' . $title . '</h1><p>' . $title . ' copy.</p></main><footer><p>© Acme</p></footer></body></html>');
+    }
+    return (new ArtifactCompiler())->compile(array('entrypoint' => 'index.html', 'files' => $files))->toWordPressSitePlanView()['wordpress_site_plan'] ?? array();
+};
+$parts = static fn(array $plan, string $area): array => array_values(array_filter($plan['template_parts'] ?? array(), static fn(array $part): bool => $area === ($part['area'] ?? null)));
+$template = static function (array $plan, string $slug): string {
+    foreach ($plan['templates'] ?? array() as $template) {
+        if ($slug === ($template['slug'] ?? null)) return (string) ($template['content'] ?? $template['canonical_block_markup'] ?? '');
+    }
+    return '';
+};
+
+// Identical headers that differ only by the capture's dialog ordinal.
+$plan = $compile(static fn(int $n): string => $links);
+$diagnostic = (string) json_encode(array_map(static fn(array $part): array => array('area' => $part['area'] ?? null, 'slug' => $part['slug'] ?? null), $plan['template_parts'] ?? array()));
+$assert(3 === count($plan['pages'] ?? array()), 'all three routes compile to pages', (string) json_encode(array_column($plan['pages'] ?? array(), 'source_path')));
+$assert(1 === count($parts($plan, 'header')), 'the header differing only by dialog ordinal becomes one template part', $diagnostic);
+$assert(1 === count($parts($plan, 'footer')), 'the footer becomes one template part', $diagnostic);
+foreach (array('page', 'front-page') as $slug) {
+    $markup = $template($plan, $slug);
+    if ('' === $markup) continue;
+    $assert(str_contains($markup, '"area":"header"') || str_contains($markup, '"slug":"header'), $slug . ' includes the header part', $markup);
+    $assert(str_contains($markup, '"area":"footer"') || str_contains($markup, '"slug":"footer'), $slug . ' includes the footer part', $markup);
+}
+
+// Negative control: dialogs that differ in content keep the header unshared.
+$control = $compile(static fn(int $n): string => '<ul><li><a href="/">Home</a></li><li><a href="/page-' . $n . '.html">Page ' . $n . '</a></li></ul>');
+$assert(0 === count($parts($control, 'header')), 'headers whose dialogs differ in content stay unshared', (string) json_encode(array_column($control['template_parts'] ?? array(), 'area')));
+$assert(1 === count($parts($control, 'footer')), 'the control footer is still shared', (string) json_encode(array_column($control['template_parts'] ?? array(), 'area')));
+
+fwrite(STDOUT, "Captured dialog ordinal shared header: {$passes} passed, {$failures} failed\n");
+exit($failures ? 1 : 0);