diff --git a/php-transformer/src/HtmlToBlocks/HtmlTransformer.php b/php-transformer/src/HtmlToBlocks/HtmlTransformer.php
index 1f0df5b..f2d6418 100644
--- a/php-transformer/src/HtmlToBlocks/HtmlTransformer.php
+++ b/php-transformer/src/HtmlToBlocks/HtmlTransformer.php
@@ -307,6 +307,7 @@ private function deduplicateNavigationBlocksRecursive(array $blocks, array &$see
 
             if ( ! empty($block['innerBlocks']) && is_array($block['innerBlocks']) ) {
                 $block['innerBlocks'] = $this->deduplicateNavigationBlocksRecursive($block['innerBlocks'], $seen);
+                $block = $this->reconcileInnerContentChildPlaceholders($block);
             }
 
             if ( 'core/navigation' === ($block['blockName'] ?? '') ) {
@@ -329,6 +330,48 @@ private function deduplicateNavigationBlocksRecursive(array $blocks, array &$see
         return $deduplicated;
     }
 
+    /**
+     * @param array<string, mixed> $block
+     * @return array<string, mixed>
+     */
+    private function reconcileInnerContentChildPlaceholders(array $block): array
+    {
+        $innerBlocks = is_array($block['innerBlocks'] ?? null) ? array_values($block['innerBlocks']) : array();
+        $innerContent = is_array($block['innerContent'] ?? null) ? array_values($block['innerContent']) : null;
+        if ( null === $innerContent ) {
+            return $block;
+        }
+
+        $placeholderCount = 0;
+        $firstPlaceholderIndex = null;
+        $lastPlaceholderIndex = null;
+        foreach ( $innerContent as $index => $part ) {
+            if ( null !== $part ) {
+                continue;
+            }
+
+            ++$placeholderCount;
+            $firstPlaceholderIndex ??= $index;
+            $lastPlaceholderIndex = $index;
+        }
+
+        if ( count($innerBlocks) === $placeholderCount ) {
+            return $block;
+        }
+
+        if ( null === $firstPlaceholderIndex || null === $lastPlaceholderIndex ) {
+            return $block;
+        }
+
+        $opening = array_slice($innerContent, 0, $firstPlaceholderIndex);
+        $closing = array_slice($innerContent, $lastPlaceholderIndex + 1);
+        $block['innerBlocks'] = $innerBlocks;
+        $block['innerContent'] = array_merge($opening, array_fill(0, count($innerBlocks), null), $closing);
+        $block['innerHTML'] = implode('', array_map(static fn ($part): string => null === $part ? '' : (string) $part, array_merge($opening, $closing)));
+
+        return $block;
+    }
+
     /**
      * @param array<string, mixed> $block
      */
diff --git a/php-transformer/tests/contract/run.php b/php-transformer/tests/contract/run.php
index d58fadf..9b2a5e9 100644
--- a/php-transformer/tests/contract/run.php
+++ b/php-transformer/tests/contract/run.php
@@ -336,6 +336,41 @@ function serialize_blocks(array $blocks): string
 $assert(str_contains($asideSerialized, 'sidebar'), 'semantic aside container preserves CSS-addressable sidebar class');
 $assert(str_contains($asideSerialized, '<!-- wp:navigation'), 'semantic aside container preserves nested navigation patterns');
 
+$assertNoInnerContentChildCountMismatch = static function (array $result, string $message) use ($assert): void {
+    $findingCodes = array_map(static fn (array $finding): string => (string) ($finding['code'] ?? ''), $result['source_reports']['wp_block_validity']['findings'] ?? array());
+    $assert(! in_array('inner_content_child_count_mismatch', $findingCodes, true), $message, implode(', ', $findingCodes));
+};
+$assertPlaceholderCountsMatchChildren = static function (array $blocks, string $path = 'blocks') use (&$assertPlaceholderCountsMatchChildren, $assert): void {
+    foreach ( $blocks as $index => $block ) {
+        if ( ! is_array($block) ) {
+            continue;
+        }
+
+        $blockPath = $path . '.' . $index;
+        $innerBlocks = is_array($block['innerBlocks'] ?? null) ? array_values($block['innerBlocks']) : array();
+        $innerContent = is_array($block['innerContent'] ?? null) ? $block['innerContent'] : array();
+        $placeholderCount = count(array_filter($innerContent, static fn ($part): bool => null === $part));
+        $assert(count($innerBlocks) === $placeholderCount, 'innerContent placeholder count matches innerBlocks count at ' . $blockPath, 'children=' . count($innerBlocks) . ' placeholders=' . $placeholderCount);
+        $assertPlaceholderCountsMatchChildren($innerBlocks, $blockPath . '.innerBlocks');
+    }
+};
+
+$deduplicatedMobileNavigation = ( new HtmlTransformer() )->transform(
+    '<header class="site-header"><nav class="primary-nav"><a href="/">Home</a><a href="/shop">Shop</a><a href="/contact">Contact</a></nav><div class="mobile-nav overlay"><div class="mobile-nav-panel"><nav class="drawer-nav"><a href="/">Home</a><a href="/shop">Shop</a><a href="/contact">Contact</a></nav></div></div></header>'
+)->toArray();
+$assert('pass' === ($deduplicatedMobileNavigation['source_reports']['wp_block_validity']['status'] ?? ''), 'deduplicated desktop/mobile navigation passes WordPress block validity');
+$assertNoInnerContentChildCountMismatch($deduplicatedMobileNavigation, 'deduplicated desktop/mobile navigation does not report innerContent child-count mismatch');
+$assertPlaceholderCountsMatchChildren($deduplicatedMobileNavigation['blocks'] ?? array());
+$assert(1 === count($deduplicatedMobileNavigation['blocks'][0]['innerBlocks'] ?? array()), 'deduplicated desktop/mobile navigation removes duplicate drawer navigation children');
+
+$deduplicatedNestedNavigation = ( new HtmlTransformer() )->transform(
+    '<main><section class="shell"><div class="desktop-wrap"><nav><a href="/">Home</a><a href="/services">Services</a></nav></div><div class="mobile-nav drawer"><div class="drawer-panel"><nav><a href="/">Home</a><a href="/services">Services</a></nav></div></div><article><h2>Services</h2><p>Copy</p></article></section></main>'
+)->toArray();
+$assert('pass' === ($deduplicatedNestedNavigation['source_reports']['wp_block_validity']['status'] ?? ''), 'nested wrapper navigation dedupe passes WordPress block validity');
+$assertNoInnerContentChildCountMismatch($deduplicatedNestedNavigation, 'nested wrapper navigation dedupe does not report innerContent child-count mismatch');
+$assertPlaceholderCountsMatchChildren($deduplicatedNestedNavigation['blocks'] ?? array());
+$assert(str_contains((string) ($deduplicatedNestedNavigation['serialized_blocks'] ?? ''), '<!-- wp:heading'), 'nested wrapper navigation dedupe preserves non-navigation siblings');
+
 $normalizedFallbacks = ( new HtmlTransformer() )->transform(
     '<main><svg><circle cx="5" cy="5" r="5"></circle></svg><svg><script>alert(1)</script></svg><script src="/app.js">init()</script><canvas>Fallback</canvas><iframe src="javascript:alert(1)"></iframe></main>'
 )->toArray();