diff --git a/php-transformer/src/ArtifactCompiler/ArtifactCompiler.php b/php-transformer/src/ArtifactCompiler/ArtifactCompiler.php
index 5abb516d..cb3fd2e5 100644
--- a/php-transformer/src/ArtifactCompiler/ArtifactCompiler.php
+++ b/php-transformer/src/ArtifactCompiler/ArtifactCompiler.php
@@ -667,6 +667,16 @@ private function finalizeArtifact(array $artifact, array $reduction): Transforme
             $sourceReports['superseded_selectors'] = $entryBlocks['superseded_selectors'];
         }
         $sourceReports['runtime_dependency_parity'] = ( new RuntimeDependencyParityReport() )->fromArtifact($normalized['files'], $html, $serializedBlocks, $entryPath, $entryBlocks['runtime_islands'], $referenceReports['asset_references'], $entryBlocks['interaction_candidates'], $entryBlocks['superseded_selectors']);
+        foreach ($sourceReports['runtime_dependency_parity']['findings'] ?? array() as $finding) {
+            if ('runtime_dependency_target_missing' !== ($finding['code'] ?? '') || 'telemetry' === ($finding['script_kind'] ?? '')) {
+                continue;
+            }
+            $diagnostics[] = $this->diagnostic('runtime_dependency_contract_failed', 'error', (string) ($finding['message'] ?? 'A required runtime DOM target is absent from generated markup.'), array_filter(array(
+                'selector' => $finding['selector'] ?? null,
+                'script_path' => $finding['script_path'] ?? null,
+                'source_path' => $finding['source_path'] ?? null,
+            ), static fn (mixed $value): bool => null !== $value && '' !== $value));
+        }
         if ( array() !== $entryBlocks['runtime_islands'] ) {
             $sourceReports['runtime_islands'] = $entryBlocks['runtime_islands'];
             if ( array() !== $runtimeIslandPackage ) {
@@ -3667,7 +3677,7 @@ private function isPresentationOnlyScriptSelector(string $script, string $select
         }
 
         $selectorPattern = preg_quote($selector, '/');
-        if ( preg_match_all('/\b(?:const|let|var)\s+([A-Za-z_$][A-Za-z0-9_$]*)\s*=\s*(?:document\s*\.\s*)?querySelector(?:All)?\s*\(\s*(["\'])' . $selectorPattern . '\2\s*\)/', $script, $assignments, PREG_SET_ORDER) ) {
+        if ( preg_match_all('/\b(?:const|let|var)\s+([A-Za-z_$][A-Za-z0-9_$]*)\s*=\s*(?:(?:document|[A-Za-z_$][A-Za-z0-9_$]*)\s*\.\s*)?querySelector(?:All)?\s*\(\s*(["\'])' . $selectorPattern . '\2\s*\)/', $script, $assignments, PREG_SET_ORDER) ) {
             foreach ($assignments as $assignment) {
                 if (preg_match('/\b' . preg_quote((string) $assignment[1], '/') . '\s*\.\s*(?:addEventListener|appendChild|removeChild|replaceChildren|insertAdjacentHTML|setAttribute|removeAttribute|toggleAttribute|getContext|submit|fetch)\b|\b' . preg_quote((string) $assignment[1], '/') . '\s*\.\s*(?:textContent|innerHTML|outerHTML|value|checked|selectedIndex|hidden|disabled|style|dataset)\b/', $script)) {
                     return false;
@@ -5619,7 +5629,7 @@ private function statusFromDiagnostics(array $diagnostics): string
                 return 'failed';
             }
 
-            if ( in_array(($diagnostic['code'] ?? ''), array('preserved_runtime_island', 'runtime_dom_contract_preserved'), true) ) {
+            if ( in_array(($diagnostic['code'] ?? ''), array('preserved_runtime_island', 'runtime_dom_contract_preserved', 'runtime_dom_contract_fallback'), true) ) {
                 continue;
             }
 
diff --git a/php-transformer/src/ArtifactCompiler/RuntimeDependencyParityReport.php b/php-transformer/src/ArtifactCompiler/RuntimeDependencyParityReport.php
index b79de405..4c8f092a 100644
--- a/php-transformer/src/ArtifactCompiler/RuntimeDependencyParityReport.php
+++ b/php-transformer/src/ArtifactCompiler/RuntimeDependencyParityReport.php
@@ -1001,7 +1001,7 @@ private function isPresentationOnlyScriptSelector(string $script, string $select
         }
 
         $selectorPattern = preg_quote($selector, '/');
-        if ( preg_match_all('/\b(?:const|let|var)\s+([A-Za-z_$][A-Za-z0-9_$]*)\s*=\s*(?:document\s*\.\s*)?querySelector(?:All)?\s*\(\s*(["\'])' . $selectorPattern . '\2\s*\)/', $script, $assignments, PREG_SET_ORDER) ) {
+        if ( preg_match_all('/\b(?:const|let|var)\s+([A-Za-z_$][A-Za-z0-9_$]*)\s*=\s*(?:(?:document|[A-Za-z_$][A-Za-z0-9_$]*)\s*\.\s*)?querySelector(?:All)?\s*\(\s*(["\'])' . $selectorPattern . '\2\s*\)/', $script, $assignments, PREG_SET_ORDER) ) {
             foreach ($assignments as $assignment) {
                 if (preg_match('/\b' . preg_quote((string) $assignment[1], '/') . '\s*\.\s*(?:addEventListener|appendChild|removeChild|replaceChildren|insertAdjacentHTML|setAttribute|removeAttribute|toggleAttribute|getContext|submit|fetch)\b|\b' . preg_quote((string) $assignment[1], '/') . '\s*\.\s*(?:textContent|innerHTML|outerHTML|value|checked|selectedIndex|hidden|disabled|style|dataset)\b/', $script)) {
                     return false;
diff --git a/php-transformer/src/HtmlToBlocks/Diagnostics/DiagnosticsCollector.php b/php-transformer/src/HtmlToBlocks/Diagnostics/DiagnosticsCollector.php
index 2265019e..061c1e2e 100644
--- a/php-transformer/src/HtmlToBlocks/Diagnostics/DiagnosticsCollector.php
+++ b/php-transformer/src/HtmlToBlocks/Diagnostics/DiagnosticsCollector.php
@@ -27,6 +27,7 @@ final class DiagnosticsCollector
      * @param array<int, array<string, mixed>>  $fallbacks            Fallback diagnostics emitted during conversion.
      * @param array<int, array<string, mixed>>  $runtimeIslands       Preserved runtime islands.
      * @param array<int, array<string, mixed>>  $runtimeDomPreservations Runtime contracts retained by native blocks.
+     * @param array<int, array<string, mixed>>  $runtimeDomFallbacks Runtime contracts retained by bounded islands.
      * @param array<string, mixed>              $blockValidityReport  Block serialization validity report.
      * @param array<string, mixed>              $semanticParityReport Semantic parity report.
      * @param array<string, mixed>              $contentRoundTripReport Content round-trip (hallucination) report.
@@ -38,6 +39,7 @@ public function collect(
         array $fallbacks,
         array $runtimeIslands,
         array $runtimeDomPreservations,
+        array $runtimeDomFallbacks,
         array $blockValidityReport,
         array $semanticParityReport,
         array $contentRoundTripReport = array()
@@ -146,6 +148,20 @@ public function collect(
             ), static fn (mixed $value): bool => null !== $value && '' !== $value);
         }
 
+        foreach ( $runtimeDomFallbacks as $fallback ) {
+            $diagnostics[] = array_filter(array(
+                'code'                => 'runtime_dom_contract_fallback',
+                'message'             => 'A script-addressed DOM contract requires a bounded runtime island because its native block cannot serialize the source element unchanged.',
+                'source'              => $transformerSource,
+                'severity'            => 'info',
+                'conversion_classification' => 'runtime_island_preserved',
+                'preservation_strategy' => 'bounded_raw_html_runtime_island',
+                'block_name'          => $fallback['block_name'] ?? null,
+                'tag'                 => $fallback['tag'] ?? null,
+                'selector'            => $fallback['selector'] ?? null,
+            ), static fn (mixed $value): bool => null !== $value && '' !== $value);
+        }
+
         foreach ( $blockValidityReport['findings'] ?? array() as $finding ) {
             if ( ! is_array($finding) ) {
                 continue;
diff --git a/php-transformer/src/HtmlToBlocks/HtmlTransformer.php b/php-transformer/src/HtmlToBlocks/HtmlTransformer.php
index cf1cfedc..af8987e6 100644
--- a/php-transformer/src/HtmlToBlocks/HtmlTransformer.php
+++ b/php-transformer/src/HtmlToBlocks/HtmlTransformer.php
@@ -833,6 +833,7 @@ public function transform(string $html, array $options = array()): TransformerRe
             $fallbacks,
             $this->runtimeIslands,
             array_values($this->runtimeDomPreservations),
+            array_values($this->runtimeDomFallbacks),
             $blockValidityReport,
             $semanticParityReport,
             $contentRoundTripReport
@@ -897,6 +898,7 @@ public function transform(string $html, array $options = array()): TransformerRe
             'head_metadata' => $headMetadata,
             'runtime_islands' => $this->runtimeIslands,
             'runtime_dom_contracts' => array_values($this->runtimeDomPreservations),
+            'runtime_dom_fallbacks' => array_values($this->runtimeDomFallbacks),
             'generated_blocks' => $this->generatedBlocks,
             'gutenberg_gaps' => $this->descriptionListBlockGenerated ? array(
                 array(
@@ -4569,7 +4571,7 @@ private function convertElement(DOMElement $element, array &$fallbacks, bool $ca
             return $this->capturedDialogBlock($element, $fallbacks);
         }
 
-        if ( $this->shouldPreserveDataAttributeRuntimeTarget($element) && ! in_array($tagName, array('p', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6'), true) ) {
+        if ( $this->shouldPreserveDataAttributeRuntimeTarget($element) ) {
             return $this->htmlPreservationBlock($element);
         }
 
@@ -4586,7 +4588,6 @@ private function convertElement(DOMElement $element, array &$fallbacks, bool $ca
 
         if ( preg_match('/^h([1-6])$/', $tagName, $matches) ) {
             $content = $this->richTextContentWithMaterializedInlineStyles($element);
-            $content = $this->richTextContentWithRuntimeRootAttributes($element, $content);
             $content = $this->headingRichTextContent($content);
             if ( $this->richTextRequiresHtmlFallbackWithoutNativeSvgImageObjects($content) ) {
                 return $this->htmlPreservationBlock($element);
@@ -4607,7 +4608,6 @@ private function convertElement(DOMElement $element, array &$fallbacks, bool $ca
                 return $marquee;
             }
             $content = $this->richTextContentWithMaterializedInlineStyles($element);
-            $content = $this->richTextContentWithRuntimeRootAttributes($element, $content);
             $inlineSvgContent = $this->richTextContentWithMaterializedSvgImages($element, $content);
             if ( null !== $inlineSvgContent ) {
                 $content = $inlineSvgContent;
@@ -5777,6 +5777,7 @@ private function createBlock(string $name, array $attrs = array(), array $innerB
                         'events'          => $this->eventMetadata($sourceElement),
                         'required_scripts' => $this->requiredScriptsForElement($sourceElement),
                     ));
+                    $this->recordRuntimeDomFallback($sourceElement, $name);
                 } else {
                     $this->recordNativeRuntimeDomPreservation($sourceElement, $name, in_array($name, array('core/paragraph', 'core/heading'), true));
                 }
@@ -12190,19 +12191,19 @@ private function recordNativeRuntimeDomPreservation(DOMElement $element, string
         }
     }
 
-    private function richTextContentWithRuntimeRootAttributes(DOMElement $element, string $content): string
+    private function recordRuntimeDomFallback(DOMElement $element, string $blockName): void
     {
-        $attributes = array();
         foreach ($this->runtimeDomSelectorsForElement($element) as $selector) {
-            if (!preg_match('/\[(data-[A-Za-z][A-Za-z0-9_-]*)/', $selector, $match)) {
+            $key = $blockName . "\n" . $selector;
+            if (isset($this->runtimeDomFallbacks[$key])) {
                 continue;
             }
-            $name = strtolower((string) $match[1]);
-            if ($element->hasAttribute($name)) {
-                $attributes[$name] = $element->getAttribute($name);
-            }
+            $this->runtimeDomFallbacks[$key] = array(
+                'block_name' => $blockName,
+                'tag' => strtolower($element->tagName),
+                'selector' => $selector,
+            );
         }
-        return array() === $attributes ? $content : '<mark' . $this->htmlAttributeString($attributes) . '>' . $content . '</mark>';
     }
 
     private function canRetainRuntimeDomContractNatively(DOMElement $element, string $blockName): bool
diff --git a/php-transformer/src/HtmlToBlocks/HtmlTransformerSession.php b/php-transformer/src/HtmlToBlocks/HtmlTransformerSession.php
index 2c58590a..a21dcf2e 100644
--- a/php-transformer/src/HtmlToBlocks/HtmlTransformerSession.php
+++ b/php-transformer/src/HtmlToBlocks/HtmlTransformerSession.php
@@ -33,6 +33,7 @@ final class HtmlTransformerSession
     public array $scriptMetadata = array();
     public array $runtimeIslands = array();
     public array $runtimeDomPreservations = array();
+    public array $runtimeDomFallbacks = array();
     public array $nativeDisclosureRootIds = array();
     public array $generatedBlocks = array();
     public bool $descriptionListBlockGenerated = false;
diff --git a/php-transformer/tests/contract/run.php b/php-transformer/tests/contract/run.php
index 643e9465..f0a5bcc3 100644
--- a/php-transformer/tests/contract/run.php
+++ b/php-transformer/tests/contract/run.php
@@ -3330,8 +3330,8 @@ public function recognize(DOMElement $element, PatternContext $context): ?Patter
     array(
         'entrypoint' => 'index.html',
         'files'      => array(
-            'index.html' => '<main><p id="clock" class="clock" data-counter="clock">0 <span id="score">score</span></p><script src="js/clock.js"></script></main>',
-            'js/clock.js' => 'document.getElementById("clock").textContent = "1"; document.querySelector(".clock").classList.add("ready"); document.querySelector("[data-counter]").textContent = "2"; document.querySelector("#score").textContent = "3";',
+            'index.html' => '<main><section class="panel"><p id="clock" class="clock">0 <span id="score">score</span></p><p data-counter="clock">Counter</p><p>Editable sibling</p></section><script src="js/clock.js"></script></main>',
+            'js/clock.js' => 'document.getElementById("clock").textContent = "1"; document.querySelector(".clock").classList.add("ready"); document.querySelector("[data-counter]").textContent = "2"; document.querySelector("#score").closest(".panel").classList.add("ready");',
         ),
     )
 )->toArray();
@@ -3339,12 +3339,13 @@ public function recognize(DOMElement $element, PatternContext $context): ?Patter
 $firstPartyRuntimeDependencies = array_column($firstPartyRuntimeContracts['source_reports']['runtime_dependency_parity']['dependencies'] ?? array(), null, 'selector');
 $firstPartyRuntimeDiagnostics = array_values(array_filter($firstPartyRuntimeContracts['diagnostics'] ?? array(), static fn (array $diagnostic): bool => 'runtime_dom_contract_preserved' === ($diagnostic['code'] ?? '')));
 $firstPartyRuntimeDiagnosticSelectors = array_column($firstPartyRuntimeDiagnostics, 'selector');
-$assert('pass' === ($firstPartyRuntimeContracts['source_reports']['runtime_dependency_parity']['status'] ?? '') && array() === ($firstPartyRuntimeContracts['source_reports']['runtime_dependency_parity']['findings'] ?? array()), 'first-party ID, class, and data-attribute runtime selectors pass only when their generated contracts are present');
-foreach (array('#clock', '.clock', '[data-counter]', '#score') as $selector) {
+$firstPartyRuntimeFallbacks = array_values(array_filter($firstPartyRuntimeContracts['diagnostics'] ?? array(), static fn (array $diagnostic): bool => 'runtime_dom_contract_fallback' === ($diagnostic['code'] ?? '')));
+$assert('pass' === ($firstPartyRuntimeContracts['source_reports']['runtime_dependency_parity']['status'] ?? '') && array() === ($firstPartyRuntimeContracts['source_reports']['runtime_dependency_parity']['findings'] ?? array()), 'first-party ID, class, closest-parent, and data-attribute runtime selectors pass only when their generated contracts are present');
+foreach (array('#clock', '.clock', '.panel', '[data-counter]', '#score') as $selector) {
     $assert(true === ($firstPartyRuntimeDependencies[$selector]['generated_present'] ?? null), 'first-party runtime dependency parity preserves ' . $selector);
-    $assert(in_array($selector, $firstPartyRuntimeDiagnosticSelectors, true), 'native preservation diagnostics identify ' . $selector);
 }
-$assert(str_contains($firstPartyRuntimeMarkup, 'id="clock" class="clock"') && str_contains($firstPartyRuntimeMarkup, '<mark data-counter="clock">') && str_contains($firstPartyRuntimeMarkup, '<span id="score">score</span>'), 'native RichText output retains required ID, class, and data attributes for first-party runtime selectors', $firstPartyRuntimeMarkup);
+$assert(in_array('#clock', $firstPartyRuntimeDiagnosticSelectors, true) && in_array('.clock', $firstPartyRuntimeDiagnosticSelectors, true) && in_array('#score', $firstPartyRuntimeDiagnosticSelectors, true) && '[data-counter]' === ($firstPartyRuntimeFallbacks[0]['selector'] ?? ''), 'per-target diagnostics distinguish native ID/class/inline preservation from data-attribute fallback');
+$assert(str_contains($firstPartyRuntimeMarkup, '<section class="wp-block-group panel">') && str_contains($firstPartyRuntimeMarkup, '<p id="clock" class="clock">0 <span id="score">score</span></p>') && str_contains($firstPartyRuntimeMarkup, '<!-- wp:html --><p data-counter="clock">Counter</p><!-- /wp:html -->') && str_contains($firstPartyRuntimeMarkup, '<p>Editable sibling</p>') && ! str_contains($firstPartyRuntimeMarkup, '<mark data-counter='), 'runtime data attributes retain their source p tag in one bounded island while native parent and siblings remain editable', $firstPartyRuntimeMarkup);
 $missingRuntimeContract = (new \Automattic\BlocksEngine\PhpTransformer\ArtifactCompiler\RuntimeDependencyParityReport())->fromArtifact(
     array(array('path' => 'js/clock.js', 'kind' => 'js', 'content' => 'document.querySelector("[data-counter]").textContent = "2";')),
     '<main><p data-counter="clock">0</p></main>',
@@ -3352,6 +3353,17 @@ public function recognize(DOMElement $element, PatternContext $context): ?Patter
     'index.html'
 );
 $assert('warning' === ($missingRuntimeContract['status'] ?? '') && 'runtime_dependency_target_missing' === ($missingRuntimeContract['findings'][0]['code'] ?? ''), 'runtime dependency parity fails closed when a required source selector is absent from generated markup');
+$missingRuntimeCompile = $compiler->compile(
+    array(
+        'entrypoint' => 'index.html',
+        'files' => array(
+            'index.html' => '<main><style data-counter="clock">.clock{color:red}</style><p>Editable</p><script src="js/clock.js"></script></main>',
+            'js/clock.js' => 'document.querySelector("[data-counter]").textContent = "2";',
+        ),
+    )
+)->toArray();
+$missingRuntimeCompileDiagnostics = array_values(array_filter($missingRuntimeCompile['diagnostics'] ?? array(), static fn (array $diagnostic): bool => 'runtime_dependency_contract_failed' === ($diagnostic['code'] ?? '')));
+$assert('failed' === ($missingRuntimeCompile['status'] ?? '') && '[data-counter]' === ($missingRuntimeCompileDiagnostics[0]['context']['selector'] ?? ''), 'ArtifactCompiler promotes required runtime selector parity failures to deterministic top-level errors');
 
 $expandedRuntimeTargetsSite = $compiler->compile(
     array(
diff --git a/php-transformer/tests/fixtures/parity/artifact-first-party-runtime-dom-contracts.json b/php-transformer/tests/fixtures/parity/artifact-first-party-runtime-dom-contracts.json
index 3c2202cc..d6079c0f 100644
--- a/php-transformer/tests/fixtures/parity/artifact-first-party-runtime-dom-contracts.json
+++ b/php-transformer/tests/fixtures/parity/artifact-first-party-runtime-dom-contracts.json
@@ -1,7 +1,7 @@
 {
   "schema": "blocks-engine/php-transformer/parity-fixture/v1",
   "name": "artifact-first-party-runtime-dom-contracts",
-  "description": "Preserves first-party ID, class, and data-attribute DOM contracts in native RichText output.",
+  "description": "Preserves native first-party ID and class contracts while bounding root data-attribute contracts to their source element.",
   "source_reference": {
     "repo": "php-transformer",
     "path": "tests/fixtures/parity/artifact-first-party-runtime-dom-contracts.json",
@@ -19,12 +19,12 @@
         {
           "path": "index.html",
           "kind": "html",
-          "content": "<main><p id=\"clock\" class=\"clock\" data-counter=\"clock\">0 <span id=\"score\">score</span></p><script src=\"js/clock.js\"></script></main>"
+          "content": "<main><section class=\"panel\"><p id=\"clock\" class=\"clock\">0 <span id=\"score\">score</span></p><p data-counter=\"clock\">Counter</p><p>Editable sibling</p></section><script src=\"js/clock.js\"></script></main>"
         },
         {
           "path": "js/clock.js",
           "kind": "js",
-          "content": "document.getElementById('clock').textContent = '1'; document.querySelector('.clock').classList.add('ready'); document.querySelector('[data-counter]').textContent = '2'; document.querySelector('#score').textContent = '3';"
+          "content": "document.getElementById('clock').textContent = '1'; document.querySelector('.clock').classList.add('ready'); document.querySelector('[data-counter]').textContent = '2'; document.querySelector('#score').closest('.panel').classList.add('ready');"
         }
       ]
     }
@@ -32,9 +32,9 @@
   "expect": [
     { "path": "status", "assert": "equals", "value": "success" },
     { "path": "source_reports.runtime_dependency_parity.status", "assert": "equals", "value": "pass" },
-    { "path": "source_reports.runtime_dependency_parity.dependencies", "assert": "count", "count": 4 },
+    { "path": "source_reports.runtime_dependency_parity.dependencies", "assert": "count", "count": 5 },
     { "path": "serialized_blocks", "assert": "contains", "value": "id=\"clock\" class=\"clock\"" },
-    { "path": "serialized_blocks", "assert": "contains", "value": "data-counter=\"clock\"" },
+    { "path": "serialized_blocks", "assert": "contains", "value": "<p data-counter=\"clock\">Counter</p>" },
     { "path": "serialized_blocks", "assert": "contains", "value": "id=\"score\"" }
   ]
 }