diff --git a/.github/workflows/solved-fixture-regression.yml b/.github/workflows/solved-fixture-regression.yml
index 95a387ed..60958d54 100644
--- a/.github/workflows/solved-fixture-regression.yml
+++ b/.github/workflows/solved-fixture-regression.yml
@@ -18,8 +18,8 @@ permissions:
 
 jobs:
   solved-site-promotion:
-    uses: Automattic/static-site-importer/.github/workflows/solved-site-promotion.yml@dbdf5413d34d8c55c034ee28a271c3ec8f53adf8
+    uses: Automattic/static-site-importer/.github/workflows/solved-site-promotion.yml@2edd49e6e03696f8a147dbac0db17d871d9a5687
     with:
-      static-site-importer-sha: dbdf5413d34d8c55c034ee28a271c3ec8f53adf8
+      static-site-importer-sha: 2edd49e6e03696f8a147dbac0db17d871d9a5687
       blocks-engine-sha: ${{ github.event.pull_request.head.sha || github.sha }}
       blocks-engine-repository: ${{ github.event.pull_request.head.repo.full_name || github.repository }}
diff --git a/php-transformer/src/ArtifactCompiler/CompanionPluginPayload.php b/php-transformer/src/ArtifactCompiler/CompanionPluginPayload.php
index 1d19d2ef..389291c3 100644
--- a/php-transformer/src/ArtifactCompiler/CompanionPluginPayload.php
+++ b/php-transformer/src/ArtifactCompiler/CompanionPluginPayload.php
@@ -4,16 +4,10 @@
 namespace Automattic\BlocksEngine\PhpTransformer\ArtifactCompiler;
 
 /**
- * Producer for the companion-plugin payload consumed by Static Site Importer.
+ * Producer for the WordPress companion-plugin payload.
  *
- * This is the producer half of the companion-plugin / plugin-materialization
- * keystone (issue #491). Slice 1 (SSI #492) built the consumer:
- * Static_Site_Importer_Companion_Plugin::scaffold() turns a payload into an
- * installable, theme-independent plugin that houses generated custom blocks
- * (registered from their own block.json) and preserved island JS. This class is
- * the producer seam: it packages the generated block definitions the artifact
- * already carries (block.json + render + view JS + assets) into a payload whose
- * shape exactly matches what scaffold() consumes.
+ * Packages generated block definitions into a product-neutral payload that a
+ * WordPress materializer can turn into a theme-independent plugin.
  *
  * Contract (consumed by scaffold(), keys it reads):
  *   - site_slug   (string)  per-site naming; SSI may override at install time.
@@ -36,12 +30,9 @@
 final class CompanionPluginPayload
 {
     /**
-     * Shared contract identifier. Mirrors the consumer schema declared by
-     * Static_Site_Importer_Companion_Plugin::PAYLOAD_SCHEMA so SSI can assert
-     * conformance. scaffold() does not require it, but stamping it makes the
-     * producer<->consumer contract explicit and greppable across repos.
+     * Product-neutral contract identifier owned by Blocks Engine.
      */
-    public const SCHEMA = 'static-site-importer/companion-plugin/v1';
+    public const SCHEMA = 'blocks-engine/wordpress-companion-plugin/v1';
 
     /**
      * Build the companion-plugin payload from detected generated blocks.
diff --git a/php-transformer/src/HtmlToBlocks/HtmlTransformer.php b/php-transformer/src/HtmlToBlocks/HtmlTransformer.php
index fb8a0715..8b7d20be 100644
--- a/php-transformer/src/HtmlToBlocks/HtmlTransformer.php
+++ b/php-transformer/src/HtmlToBlocks/HtmlTransformer.php
@@ -15400,29 +15400,115 @@ private function responsiveMediaBlock(DOMElement $element): array
     /** @return array<string, mixed>|null */
     private function capturedMediaLayoutBoundaryBlock(DOMElement $element): ?array
     {
-        if ( 'main' !== strtolower($element->tagName)
+        if ( ! in_array(strtolower($element->tagName), array('main', 'article', 'section', 'div', 'figure'), true)
             || $this->isRuntimeDomTarget($element)
             || $this->hasRuntimeTargetInSubtree($element)
             || $this->hasLayoutGeometryProofInSubtree($element)
             || $this->sourceElementNestingDepth($element) <= self::MAX_CAPTURED_LAYOUT_SOURCE_NESTING
             || ! $this->hasCapturedMediaContent($element)
+            || ('main' !== strtolower($element->tagName) && '' === trim((string) $element->textContent))
         ) {
             return null;
         }
 
-        if ( ! $this->responsiveMediaBlockGenerated ) {
-            $this->generatedBlocks[] = ( new ResponsiveMediaBlockGenerator() )->definition($this->generatedBlockNamespace);
-            $this->responsiveMediaBlockGenerated = true;
+        if ( ! $this->isStaticLayoutV1($element) ) {
+            return null;
+        }
+
+        if ( ! $this->responsiveLayoutBlockGenerated ) {
+            $this->generatedBlocks[] = ( new ResponsiveLayoutBlockGenerator() )->definition($this->generatedBlockNamespace);
+            $this->responsiveLayoutBlockGenerated = true;
         }
 
         return $this->createBlock(
-            $this->generatedBlockNamespace . '/' . ResponsiveMediaBlockGenerator::LOCAL_NAME,
-            array( 'content' => $this->safeFallbackHtml($element), 'kind' => 'layout' ),
+            $this->generatedBlockNamespace . '/' . ResponsiveLayoutBlockGenerator::LOCAL_NAME,
+            array( 'content' => $this->staticLayoutHtml($element) ),
             array(),
             $element
         );
     }
 
+    /**
+     * The responsive-layout renderer accepts this fixed static-layout-v1
+     * subset. Keep admission narrower than fallback sanitizing
+     * so a captured layout never depends on stripped source semantics.
+     */
+    private function isStaticLayoutV1(DOMElement $element): bool
+    {
+        $tags = array(
+            'main', 'article', 'aside', 'section', 'header', 'footer', 'nav', 'div', 'figure',
+            'figcaption', 'p', 'span', 'strong', 'em', 'b', 'i', 'small', 'br',
+            'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'a', 'button', 'ul', 'ol', 'li',
+            'dl', 'dt', 'dd', 'picture', 'source', 'img', 'video', 'audio',
+            'svg', 'defs', 'symbol', 'lineargradient', 'radialgradient', 'stop', 'clippath',
+            'mask', 'use', 'g', 'path', 'circle', 'ellipse', 'line', 'polyline', 'polygon',
+            'rect', 'text', 'tspan', 'title', 'desc', 'link',
+        );
+        $globalAttributes = array(
+            'class', 'id', 'role', 'title', 'style', 'tabindex', 'dir', 'lang', 'hidden', 'xml:lang',
+            'aria-controls', 'aria-current', 'aria-describedby', 'aria-details', 'aria-expanded',
+            'aria-hidden', 'aria-label', 'aria-labelledby', 'aria-live',
+        );
+        $tagAttributes = array(
+            'a' => array('download', 'href', 'target', 'rel'),
+            'button' => array('disabled', 'name', 'type', 'value'),
+            'img' => array('src', 'alt', 'width', 'height', 'loading', 'decoding', 'fetchpriority', 'longdesc', 'srcset', 'sizes', 'usemap'),
+            'source' => array('src', 'srcset', 'sizes', 'media', 'type'),
+            'video' => array('autoplay', 'controls', 'height', 'loop', 'muted', 'playsinline', 'poster', 'preload', 'src', 'width'),
+            'audio' => array('autoplay', 'controls', 'loop', 'muted', 'preload', 'src'),
+            'svg' => array('fill', 'stroke', 'viewbox', 'width', 'height', 'focusable', 'preserveaspectratio', 'xmlns', 'xmlns:xlink'),
+            'symbol' => array('viewbox'),
+            'lineargradient' => array('gradientunits', 'x1', 'x2', 'y1', 'y2'),
+            'radialgradient' => array('cx', 'cy', 'r'),
+            'stop' => array('offset', 'stop-color', 'stop-opacity'),
+            'use' => array('href', 'xlink:href'),
+            'g' => array('clip-path', 'fill', 'fill-opacity', 'opacity', 'stroke', 'stroke-width', 'transform'),
+            'path' => array('d', 'fill', 'fill-rule', 'opacity', 'stroke', 'stroke-width', 'stroke-linecap', 'stroke-linejoin', 'transform'),
+            'circle' => array('cx', 'cy', 'r', 'fill', 'opacity', 'stroke', 'stroke-width'),
+            'ellipse' => array('cx', 'cy', 'rx', 'ry', 'fill', 'opacity', 'stroke', 'stroke-width'),
+            'line' => array('x1', 'x2', 'y1', 'y2', 'fill', 'stroke', 'stroke-width', 'stroke-linecap'),
+            'polyline' => array('points', 'fill', 'stroke', 'stroke-width', 'stroke-linecap', 'stroke-linejoin'),
+            'polygon' => array('points', 'fill', 'stroke', 'stroke-width', 'stroke-linecap', 'stroke-linejoin'),
+            'rect' => array('x', 'y', 'width', 'height', 'rx', 'ry', 'fill', 'opacity', 'stroke', 'stroke-width'),
+            'text' => array('fill', 'font-family', 'font-size', 'font-weight', 'text-anchor', 'x', 'y'),
+            'tspan' => array('dx', 'dy', 'fill', 'x', 'y'),
+            'link' => array('href', 'rel'),
+        );
+
+        foreach (array_merge(array($element), $this->descendantElements($element)) as $candidate) {
+            $tag = strtolower($candidate->tagName);
+            $customElement = (bool) preg_match('/^[a-z][a-z0-9]*-[a-z0-9-]+$/D', $tag);
+            if ( (! $customElement && ! in_array($tag, $tags, true)) || $this->isDeclaredRuntimeDomTarget($candidate) || array() !== $this->eventMetadata($candidate) ) {
+                return false;
+            }
+            if ('svg' === $tag && ! $this->isSafeSvgContent($this->outerHtml($candidate))) {
+                return false;
+            }
+            if ('link' === $tag && ('stylesheet' !== strtolower($this->attr($candidate, 'rel')) || ! $this->hasAncestorTag($candidate, array('defs')) || ! $this->hasAncestorTag($candidate, array('svg')) || ! $this->safeFallbackUrl($this->attr($candidate, 'href'), 'href'))) {
+                return false;
+            }
+
+            $allowed = array_merge($globalAttributes, $tagAttributes[$tag] ?? array());
+            foreach ($this->htmlAttributes($candidate) as $attribute => $value) {
+                $attribute = strtolower($attribute);
+                if ( (! str_starts_with($attribute, 'data-') && ! str_starts_with($attribute, 'aria-') && ! in_array($attribute, $allowed, true))
+                    || str_starts_with($attribute, 'data-wp-')
+                    || ('srcset' === $attribute && $this->safeFallbackSrcset($value) !== $value)
+                    || (in_array($attribute, array('href', 'src'), true) && ! $this->safeFallbackUrl($value, $attribute))
+                ) {
+                    return false;
+                }
+            }
+        }
+
+        return true;
+    }
+
+    private function staticLayoutHtml(DOMElement $element): string
+    {
+        return preg_replace('/<link\b[^>]*\/?\s*>/i', '', $this->safeFallbackHtml($element)) ?? '';
+    }
+
     private function hasLayoutGeometryProofInSubtree(DOMElement $element): bool
     {
         $prefix = $this->elementSelector($element) . ' > ';
@@ -15444,13 +15530,30 @@ private function hasCapturedMediaContent(DOMElement $element): bool
     private function hasRuntimeTargetInSubtree(DOMElement $element): bool
     {
         foreach ( $element->getElementsByTagName('*') as $descendant ) {
-            if ( $descendant instanceof DOMElement && $this->isRuntimeDomTarget($descendant) ) {
+            if ( $descendant instanceof DOMElement && $this->isDeclaredRuntimeDomTarget($descendant) ) {
                 return true;
             }
         }
         return false;
     }
 
+    private function isDeclaredRuntimeDomTarget(DOMElement $element): bool
+    {
+        foreach (array_keys($this->runtimeDomSelectors) as $selector) {
+            if (str_starts_with((string) $selector, '#') && substr((string) $selector, 1) === $this->attr($element, 'id')) {
+                return true;
+            }
+            if (str_starts_with((string) $selector, '.') && in_array(substr((string) $selector, 1), $this->classNames($element), true)) {
+                return true;
+            }
+            if ($this->elementMatchesRuntimeSelector($element, (string) $selector)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     private function sourceElementNestingDepth(DOMElement $element): int
     {
         $depth = 0;
diff --git a/php-transformer/src/HtmlToBlocks/HtmlTransformerSession.php b/php-transformer/src/HtmlToBlocks/HtmlTransformerSession.php
index adb3b5be..ee5e60e7 100644
--- a/php-transformer/src/HtmlToBlocks/HtmlTransformerSession.php
+++ b/php-transformer/src/HtmlToBlocks/HtmlTransformerSession.php
@@ -43,6 +43,7 @@ final class HtmlTransformerSession
     public bool $formSelectBlockGenerated = false;
     public bool $formInputBlockGenerated = false;
     public bool $responsiveMediaBlockGenerated = false;
+    public bool $responsiveLayoutBlockGenerated = false;
     public bool $authoredMarqueeBlockGenerated = false;
     public bool $emptyRuntimeTargetGenerated = false;
     public bool $capturedDialogBlockGenerated = false;
diff --git a/php-transformer/src/HtmlToBlocks/ResponsiveLayoutBlockGenerator.php b/php-transformer/src/HtmlToBlocks/ResponsiveLayoutBlockGenerator.php
new file mode 100644
index 00000000..435a9c36
--- /dev/null
+++ b/php-transformer/src/HtmlToBlocks/ResponsiveLayoutBlockGenerator.php
@@ -0,0 +1,65 @@
+<?php
+declare(strict_types=1);
+
+namespace Automattic\BlocksEngine\PhpTransformer\HtmlToBlocks;
+
+/** Builds the bounded companion block for captured static layout markup. */
+final class ResponsiveLayoutBlockGenerator
+{
+    public const LOCAL_NAME = 'responsive-layout';
+    public const RENDERER = 'blocks-engine/responsive-layout/v1';
+
+    /** @return array<string, mixed> */
+    public function blockJson(string $namespace): array
+    {
+        return array(
+            'apiVersion' => 3,
+            'name' => $namespace . '/' . self::LOCAL_NAME,
+            'title' => 'Responsive Layout',
+            'category' => 'design',
+            'description' => 'An editable captured static layout boundary.',
+            'editorScript' => 'file:./index.js',
+            'attributes' => array(
+                'content' => array( 'type' => 'string', 'default' => '', 'role' => 'content' ),
+            ),
+            'supports' => array( 'html' => false ),
+        );
+    }
+
+    /** @return array<string, string> */
+    public function assets(string $blockName): array
+    {
+        $script = <<<'JS'
+( function( blocks, blockEditor, components, element ) {
+    var createElement = element.createElement;
+    function edit( props ) {
+        return createElement( 'div', blockEditor.useBlockProps(), createElement( components.TextareaControl, {
+            label: 'Captured layout HTML',
+            value: props.attributes.content || '',
+            onChange: function( content ) { props.setAttributes( { content: content } ); }
+        } ) );
+    }
+    blocks.registerBlockType( '__BLOCK_NAME__', {
+        attributes: { content: { type: 'string', default: '', role: 'content' } },
+        supports: { html: false },
+        edit: edit,
+        save: function() { return null; }
+    } );
+} )( window.wp.blocks, window.wp.blockEditor, window.wp.components, window.wp.element );
+JS;
+
+        return array( 'index.js' => str_replace('__BLOCK_NAME__', $blockName, $script) );
+    }
+
+    /** @return array<string, mixed> */
+    public function definition(string $namespace): array
+    {
+        return array(
+            'name' => self::LOCAL_NAME,
+            'block_json' => $this->blockJson($namespace),
+            'renderer' => self::RENDERER,
+            'assets' => $this->assets($namespace . '/' . self::LOCAL_NAME),
+            'script_dependencies' => array( 'index.js' => array( 'wp-blocks', 'wp-block-editor', 'wp-components', 'wp-element' ) ),
+        );
+    }
+}
diff --git a/php-transformer/src/HtmlToBlocks/ResponsiveMediaBlockGenerator.php b/php-transformer/src/HtmlToBlocks/ResponsiveMediaBlockGenerator.php
index e88b40c1..03576a43 100644
--- a/php-transformer/src/HtmlToBlocks/ResponsiveMediaBlockGenerator.php
+++ b/php-transformer/src/HtmlToBlocks/ResponsiveMediaBlockGenerator.php
@@ -7,7 +7,7 @@
 final class ResponsiveMediaBlockGenerator
 {
     public const LOCAL_NAME = 'responsive-media';
-    public const RENDERER = 'static-site-importer/responsive-media/v1';
+    public const RENDERER = 'blocks-engine/responsive-media/v1';
 
     /** @return array<string, mixed> */
     public function blockJson(string $namespace): array
diff --git a/php-transformer/src/HtmlToBlocks/Support/DomHelpersTrait.php b/php-transformer/src/HtmlToBlocks/Support/DomHelpersTrait.php
index 39d3363e..4a24714f 100644
--- a/php-transformer/src/HtmlToBlocks/Support/DomHelpersTrait.php
+++ b/php-transformer/src/HtmlToBlocks/Support/DomHelpersTrait.php
@@ -251,6 +251,7 @@ private function materializeFallbackSourceTagMarker(DOMElement $element): void
     private function safeFallbackHtmlString(string $html): string
     {
         $html = preg_replace('@<(script|style)[^>]*?>.*?</\\1>@si', '', $html) ?? '';
+        $html = preg_replace('@<link\b[^>]*\/?>@si', '', $html) ?? '';
         $html = preg_replace('/\s+on[a-z]+\s*=\s*("[^"]*"|\'[^\']*\'|[^\s>]+)/i', '', $html) ?? '';
         $html = preg_replace_callback(
             '/\s+([a-zA-Z_:][\w:.-]*)\s*=\s*("([^"]*)"|\'([^\']*)\'|([^\s>]+))/i',
diff --git a/php-transformer/tests/contract/run.php b/php-transformer/tests/contract/run.php
index 6a9938bd..ccdae85f 100644
--- a/php-transformer/tests/contract/run.php
+++ b/php-transformer/tests/contract/run.php
@@ -4270,7 +4270,7 @@ public function recognize(DOMElement $element, PatternContext $context): ?Patter
 )->toArray();
 $companionPayload = $companion['source_reports']['companion_plugin_payload'] ?? null;
 $assert(is_array($companionPayload), 'companion_plugin_payload is emitted when a generated block is present');
-$assert('static-site-importer/companion-plugin/v1' === ($companionPayload['schema'] ?? ''), 'companion payload stamps the shared consumer schema');
+$assert('blocks-engine/wordpress-companion-plugin/v1' === ($companionPayload['schema'] ?? ''), 'companion payload stamps the producer-owned WordPress contract');
 $assert('acme' === ($companionPayload['site_slug'] ?? ''), 'companion payload derives site_slug from the artifact');
 $assert('Acme Co' === ($companionPayload['site_name'] ?? ''), 'companion payload derives site_name from the artifact');
 $assert(array() === ($companionPayload['preserved_js'] ?? null), 'companion payload exposes an empty preserved_js slot');
diff --git a/php-transformer/tests/contract/staged-artifact-compilation.php b/php-transformer/tests/contract/staged-artifact-compilation.php
index e2ab87be..fcb35e74 100644
--- a/php-transformer/tests/contract/staged-artifact-compilation.php
+++ b/php-transformer/tests/contract/staged-artifact-compilation.php
@@ -446,7 +446,7 @@ public function read(array $reference): string { $this->reads[] = $reference['id
 $layoutShared = $layoutCompiler->prepareShared($layoutArtifact);
 $layoutStaged = $layoutCompiler->compose($layoutShared, array($layoutCompiler->compilePage($layoutArtifact, $layoutShared, 'index.html')))->toArray();
 $layoutPage = $layoutWhole['source_reports']['compiled_site']['pages'][0] ?? array();
-$assert('passed' === ($layoutWhole['source_reports']['editability_policy']['status'] ?? null) && str_contains((string) ($layoutPage['block_markup'] ?? ''), '"kind":"layout"'), 'A deep semantic media main compiles as one typed layout boundary under the unchanged editability policy.');
+$assert('passed' === ($layoutWhole['source_reports']['editability_policy']['status'] ?? null) && str_contains((string) ($layoutPage['block_markup'] ?? ''), '<!-- wp:custom/responsive-layout {"content":'), 'A deep semantic media main compiles as one dedicated typed layout boundary under the unchanged editability policy.');
 $assert($canonical($layoutWhole) === $canonical($layoutStaged), 'Typed captured layout boundaries preserve direct and staged canonical equivalence.');
 
 fwrite(STDOUT, "Staged artifact compilation contract passed\n");
diff --git a/php-transformer/tests/fixtures/parity/artifact-custom-block-companion-payload.json b/php-transformer/tests/fixtures/parity/artifact-custom-block-companion-payload.json
index 8b17df1b..2006b90c 100644
--- a/php-transformer/tests/fixtures/parity/artifact-custom-block-companion-payload.json
+++ b/php-transformer/tests/fixtures/parity/artifact-custom-block-companion-payload.json
@@ -28,7 +28,7 @@
   },
   "expect": [
     { "path": "status", "assert": "equals", "value": "success" },
-    { "path": "source_reports.companion_plugin_payload.schema", "assert": "equals", "value": "static-site-importer/companion-plugin/v1" },
+    { "path": "source_reports.companion_plugin_payload.schema", "assert": "equals", "value": "blocks-engine/wordpress-companion-plugin/v1" },
     { "path": "source_reports.companion_plugin_payload.site_slug", "assert": "equals", "value": "acme-co" },
     { "path": "source_reports.companion_plugin_payload.blocks", "assert": "count", "count": 1 },
     { "path": "source_reports.companion_plugin_payload.blocks.0.name", "assert": "equals", "value": "collection-42ba83f51ffea3a7df69ca6f8c29d50848fd6a809917172303a2c79f3802c9bd" },
diff --git a/php-transformer/tests/fixtures/parity/html-deep-semantic-responsive-layout.json b/php-transformer/tests/fixtures/parity/html-deep-semantic-responsive-layout.json
new file mode 100644
index 00000000..79dd92f8
--- /dev/null
+++ b/php-transformer/tests/fixtures/parity/html-deep-semantic-responsive-layout.json
@@ -0,0 +1,31 @@
+{
+  "schema": "blocks-engine/php-transformer/parity-fixture/v1",
+  "name": "html-deep-semantic-responsive-layout",
+  "description": "Captures a deeply nested static semantic main through a dedicated typed responsive-layout boundary.",
+  "source_reference": {
+    "repo": "blocks-engine",
+    "path": "php-transformer/tests/fixtures/parity/html-deep-semantic-responsive-layout.json",
+    "notes": "Product-neutral contract coverage for deep static layout boundaries containing headings, groups, links, raster media, and safe inline SVG."
+  },
+  "legacy_comparison": {
+    "skip": true,
+    "reason": "This released typed boundary is covered by producer contract tests."
+  },
+  "operation": "html_transformer.transform",
+  "input": {
+    "content": "<main class=\"puffin-story\"><div class=\"layer-0\"><div class=\"layer-1\"><div class=\"layer-2\"><div class=\"layer-3\"><div class=\"layer-4\"><div class=\"layer-5\"><div class=\"layer-6\"><div class=\"layer-7\"><div class=\"layer-8\"><div class=\"layer-9\"><div class=\"layer-10\"><div class=\"layer-11\"><div class=\"layer-12\"><div class=\"layer-13\"><div class=\"layer-14\"><div class=\"layer-15\"><div class=\"layer-16\"><div class=\"layer-17\"><div class=\"layer-18\"><div class=\"layer-19\"><div class=\"layer-20\"><header><nav aria-label=\"Primary\"><a href=\"/about\">About</a></nav></header><section><h1>Deep story</h1><p>Readable <strong>copy</strong>.</p><img src=\"hero.jpg\" alt=\"Hero\"><svg viewBox=\"0 0 10 10\" role=\"img\" aria-label=\"Mark\"><path d=\"M0 0L10 10\" stroke=\"#000\"></path></svg></section></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></main>"
+  },
+  "expected_blocks": [
+    { "path": "blocks.0", "name": "custom/responsive-layout" }
+  ],
+  "expected_fallbacks": [],
+  "expect": [
+    { "path": "status", "assert": "equals", "value": "success" },
+    { "path": "blocks", "assert": "count", "count": 1 },
+    { "path": "fallbacks", "assert": "count", "count": 0 },
+    { "path": "blocks.0.attrs.content", "assert": "contains", "value": "<h1>Deep story</h1>" },
+    { "path": "blocks.0.attrs.content", "assert": "contains", "value": "<svg viewbox=\"0 0 10 10\" role=\"img\" aria-label=\"Mark\">" },
+    { "path": "blocks.0.attrs.content", "assert": "contains", "value": "layer-20" },
+    { "path": "source_reports.generated_blocks.0.renderer", "assert": "equals", "value": "blocks-engine/responsive-layout/v1" }
+  ]
+}
diff --git a/php-transformer/tests/unit/inert-capture-scaffolding.php b/php-transformer/tests/unit/inert-capture-scaffolding.php
index 89e2e9e5..0ea3916d 100644
--- a/php-transformer/tests/unit/inert-capture-scaffolding.php
+++ b/php-transformer/tests/unit/inert-capture-scaffolding.php
@@ -29,6 +29,10 @@
 $materializedSvg = implode("\n", array_map(static fn (array $asset): string => (string) ($asset['content'] ?? ''), array_filter($referencedStore['assets'] ?? array(), static fn (array $asset): bool => 'inline-svg' === ($asset['source'] ?? ''))));
 $assert(str_contains($materializedSvg, 'id="mark"') && str_contains($materializedSvg, 'href="#mark"'), 'referenced SVG symbols remain available to materialized images');
 
+$capturedCollection = $transform('<main><fluid-columns-repeater><div><svg viewBox="0 0 1 1"><defs><link rel="stylesheet" href="/assets/icon.css"></defs><path d="M0 0h1v1z"/></svg><p>One</p></div><div><p>Two</p></div></fluid-columns-repeater></main>');
+$generatedRender = implode("\n", array_map(static fn (array $block): string => (string) ($block['render'] ?? ''), $capturedCollection['source_reports']['generated_blocks'] ?? array()));
+$assert('' !== $generatedRender && ! str_contains($generatedRender, '<link'), 'generated custom blocks strip captured stylesheet links from nested SVG markup');
+
 $visibleIframe = $transform('<main><iframe title="HubSpot form" src="https://forms.hsforms.com/widget" width="600" height="400"></iframe></main>');
 $iframeFallbacks = array_values(array_filter($visibleIframe['fallbacks'] ?? array(), static fn (array $fallback): bool => 'iframe' === ($fallback['tag'] ?? '')));
 $assert(1 === count($iframeFallbacks), 'visible HubSpot iframe remains a bounded external embed');
diff --git a/php-transformer/tests/unit/responsive-media-block.php b/php-transformer/tests/unit/responsive-media-block.php
index 36766b32..6f66c4cd 100644
--- a/php-transformer/tests/unit/responsive-media-block.php
+++ b/php-transformer/tests/unit/responsive-media-block.php
@@ -5,6 +5,7 @@
 
 use Automattic\BlocksEngine\PhpTransformer\ArtifactCompiler\CompanionPluginPayload;
 use Automattic\BlocksEngine\PhpTransformer\HtmlToBlocks\HtmlTransformer;
+use Automattic\BlocksEngine\PhpTransformer\HtmlToBlocks\ResponsiveLayoutBlockGenerator;
 use Automattic\BlocksEngine\PhpTransformer\HtmlToBlocks\ResponsiveMediaBlockGenerator;
 
 $assert = static function (bool $condition, string $message): void {
@@ -41,6 +42,15 @@
 $assert(($definition['block_json']['attributes'] ?? null) === $editorAttributes, 'the editor registration attribute schema exactly matches generated block metadata');
 $assert('content' === ($editorAttributes['content']['role'] ?? null), 'the editor registration marks responsive media HTML as Gutenberg content');
 $assert('media' === ($editorAttributes['kind']['default'] ?? null), 'the editor registration carries the typed captured-boundary kind');
+$assert('string' === ($definition['block_json']['attributes']['kind']['type'] ?? null) && 'media' === ($definition['block_json']['attributes']['kind']['default'] ?? null), 'producer metadata declares the responsive-media boundary kind schema');
+
+$layoutDefinition = ( new ResponsiveLayoutBlockGenerator() )->definition('ssi-example');
+$assert('ssi-example/responsive-layout' === ($layoutDefinition['block_json']['name'] ?? null), 'one namespaced responsive-layout block type is defined');
+$assert(array('content') === array_keys($layoutDefinition['block_json']['attributes'] ?? array()), 'responsive layout declares a dedicated content-only schema');
+$assert(ResponsiveLayoutBlockGenerator::RENDERER === ($layoutDefinition['renderer'] ?? null), 'responsive layout delegates rendering through its producer-owned capability');
+$layoutEditor = (string) ($layoutDefinition['assets']['index.js'] ?? '');
+$layoutEditorAttributes = json_decode((string) shell_exec('node -e ' . escapeshellarg($editorSchemaRunner) . ' ' . escapeshellarg(base64_encode($layoutEditor))), true);
+$assert(($layoutDefinition['block_json']['attributes'] ?? null) === $layoutEditorAttributes, 'responsive layout editor registration matches generated block metadata');
 
 $source = '<a class="social" href="/profile" target="_blank" rel="noopener" aria-label="Profile"><picture class="hero"><source media="(min-width: 800px)" type="image/webp" srcset="hero,wide.webp 1200w, hero.webp 600w" sizes="100vw"><img class="avatar" src="hero.jpg" srcset="hero.jpg 1x, hero-2x.jpg 2x" sizes="100vw" width="44" height="44" alt="Profile"></picture></a>';
 $result = ( new HtmlTransformer() )->transform($source)->toArray();
@@ -56,7 +66,7 @@
 $wrapped = ( new HtmlTransformer() )->transform($wrappedSource)->toArray();
 $wrappedContent = (string) ($wrapped['blocks'][0]['attrs']['content'] ?? '');
 $assert('custom/responsive-media' === ($wrapped['blocks'][0]['blockName'] ?? null), 'an image-only custom-element carrier inside a link uses responsive media');
-$assert(str_contains($wrappedContent, '<wow-image') && str_contains($wrappedContent, '<img') && str_contains($wrappedContent, 'href="/profile"'), 'the linked custom carrier retains its bounded source markup for SSI rendering');
+$assert(str_contains($wrappedContent, '<wow-image') && str_contains($wrappedContent, '<img') && str_contains($wrappedContent, 'href="/profile"'), 'the linked custom carrier retains its bounded source markup for WordPress rendering');
 
 $nestedWrappedSource = '<a href="/profile" aria-label="Profile"><div class="crop" style="overflow:hidden"><wow-image data-image-info="bounded"><img src="profile.png" width="30" height="30" alt="Profile"></wow-image></div></a>';
 $nestedWrapped = ( new HtmlTransformer() )->transform($nestedWrappedSource)->toArray();
@@ -67,26 +77,43 @@
 $labeledWrapper = ( new HtmlTransformer() )->transform('<a href="/profile"><div><wow-image><img src="profile.png" alt="Profile"></wow-image><span>Profile</span></div></a>')->toArray();
 $assert('custom/responsive-media' !== ($labeledWrapper['blocks'][0]['blockName'] ?? null), 'a linked image wrapper with authored label content is not collapsed into responsive media');
 
-$layoutHtml = '<main class="story"><div class="shell">';
+$layoutHtml = '<main class="puffin-story"><div class="shell">';
 for ($depth = 0; $depth < 21; ++$depth) $layoutHtml .= '<div class="layer-' . $depth . '">';
-$layoutHtml .= '<a href="/story" aria-label="Story"><img src="story.jpg" alt="Story"></a>';
+$layoutHtml .= '<h1>Deep story</h1><section data-hook="post-list" style="padding:20px"><ol><li><button type="button">Read more</button><a href="/story" aria-label="Story">Read the story</a></li></ol><wow-image data-hook="image"><img src="story.jpg" alt="Story" fetchpriority="high"></wow-image><svg viewBox="0 0 10 10" role="img" aria-label="Mark"><defs><link rel="stylesheet" href="/layout.css"><path id="mark" d="M0 0L10 10"></path></defs><use href="#mark"></use></svg></section>';
 for ($depth = 0; $depth < 21; ++$depth) $layoutHtml .= '</div>';
 $layoutHtml .= '</div></main>';
 $layout = ( new HtmlTransformer() )->transform($layoutHtml)->toArray();
 $layoutBlock = $layout['blocks'][0] ?? array();
-$assert('custom/responsive-media' === ($layoutBlock['blockName'] ?? null) && 'layout' === ($layoutBlock['attrs']['kind'] ?? null), 'A deep semantic media main uses the existing companion as a typed layout boundary.');
-$assert(str_contains((string) ($layoutBlock['attrs']['content'] ?? ''), 'href="/story"') && str_contains((string) ($layoutBlock['attrs']['content'] ?? ''), 'aria-label="Story"') && str_contains((string) ($layoutBlock['attrs']['content'] ?? ''), 'layer-20'), 'A captured layout boundary retains links, accessibility, and authored selector identity.');
+$assert('custom/responsive-layout' === ($layoutBlock['blockName'] ?? null) && ! isset($layoutBlock['attrs']['kind']), 'A deep static layout uses its dedicated companion boundary.');
+$assert(str_contains((string) ($layoutBlock['attrs']['content'] ?? ''), '<h1>Deep story</h1>') && str_contains((string) ($layoutBlock['attrs']['content'] ?? ''), '<button type="button">Read more</button>') && str_contains((string) ($layoutBlock['attrs']['content'] ?? ''), '<img src="story.jpg" alt="Story" fetchpriority="high">') && str_contains((string) ($layoutBlock['attrs']['content'] ?? ''), '<wow-image data-hook="image">') && str_contains((string) ($layoutBlock['attrs']['content'] ?? ''), '<svg viewbox="0 0 10 10" role="img" aria-label="Mark">') && str_contains((string) ($layoutBlock['attrs']['content'] ?? ''), 'layer-20'), 'A captured Puffin-like layout retains static lists, controls, inert custom elements, media hints, safe SVG, accessibility, and authored selector identity.');
+$assert(! str_contains((string) ($layoutBlock['attrs']['content'] ?? ''), '<link'), 'A captured layout removes inert SVG stylesheet carriers after their CSS asset has been projected.');
 $assert('pass' === ($layout['source_reports']['wp_block_validity']['status'] ?? null), 'A captured layout boundary remains valid Gutenberg block markup.');
 $layoutPayload = ( new CompanionPluginPayload() )->fromBlockTypes(array(), array(), array(), $layout['source_reports']['generated_blocks'] ?? array());
-$assert(array( 'content', 'kind' ) === array_keys($layoutPayload['blocks'][0]['block_json']['attributes'] ?? array()) && ResponsiveMediaBlockGenerator::RENDERER === ($layoutPayload['blocks'][0]['renderer'] ?? null) && ! isset($layoutPayload['blocks'][0]['render']), 'The companion payload preserves the bounded typed layout schema and audited renderer only.');
+$assert(array( 'content' ) === array_keys($layoutPayload['blocks'][0]['block_json']['attributes'] ?? array()) && ResponsiveLayoutBlockGenerator::RENDERER === ($layoutPayload['blocks'][0]['renderer'] ?? null) && ! isset($layoutPayload['blocks'][0]['render']), 'The companion payload preserves the dedicated typed layout schema and audited renderer only.');
 
 $shallow = ( new HtmlTransformer() )->transform('<main><div><img src="story.jpg" alt="Story"></div></main>')->toArray();
 $assert('custom/responsive-media' !== ($shallow['blocks'][0]['blockName'] ?? null), 'A shallow media main remains on native conversion paths.');
 
-$runtimeLayout = ( new HtmlTransformer() )->transform($layoutHtml, array('runtime_dom_selectors' => array('.story')))->toArray();
-$assert('custom/responsive-media' !== ($runtimeLayout['blocks'][0]['blockName'] ?? null), 'A declared runtime layout boundary remains addressable instead of being captured.');
+$runtimeLayout = ( new HtmlTransformer() )->transform($layoutHtml, array('runtime_dom_selectors' => array('.puffin-story')))->toArray();
+$assert('custom/responsive-layout' !== ($runtimeLayout['blocks'][0]['blockName'] ?? null), 'A declared runtime layout boundary remains addressable instead of being captured.');
 
 $nestedRuntimeLayout = ( new HtmlTransformer() )->transform($layoutHtml, array('runtime_dom_selectors' => array('.layer-20')))->toArray();
-$assert('custom/responsive-media' !== ($nestedRuntimeLayout['blocks'][0]['blockName'] ?? null), 'A declared runtime descendant remains addressable instead of being captured.');
+$assert('custom/responsive-layout' !== ($nestedRuntimeLayout['blocks'][0]['blockName'] ?? null), 'A declared runtime descendant remains addressable instead of being captured.');
+
+foreach (array(
+    'form' => array('<form action="/contact"><input name="email"><button>Send</button></form>', null),
+    'table' => array('<table><tr><td>Cell</td></tr></table>', '<!-- wp:table'),
+    'details' => array('<details><summary>More</summary><p>Details</p></details>', '<!-- wp:details'),
+) as $name => $case) {
+    list($unsupported, $nativeMarker) = $case;
+    $unsupportedHtml = str_replace('</section>', $unsupported . '</section>', $layoutHtml);
+    $unsupportedResult = ( new HtmlTransformer() )->transform($unsupportedHtml)->toArray();
+    $assert('custom/responsive-layout' !== ($unsupportedResult['blocks'][0]['blockName'] ?? null), 'A deep layout with unsupported ' . $name . ' semantics is not silently captured.');
+    if (is_string($nativeMarker)) {
+        $assert(str_contains((string) ($unsupportedResult['serialized_blocks'] ?? ''), $nativeMarker), 'An unsupported deep ' . $name . ' remains on its native conversion path.');
+    }
+}
+$formResult = ( new HtmlTransformer() )->transform(str_replace('</section>', '<form action="/contact"><input name="email"></form></section>', $layoutHtml))->toArray();
+$assert(array() !== ($formResult['fallbacks'] ?? array()), 'An unsupported deep form produces an observable conversion finding.');
 
 fwrite(STDOUT, "Responsive media companion tests passed\n");