diff --git a/core/core.services.yml b/core/core.services.yml
index 6508178272f..bc94ced6371 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -943,7 +943,7 @@ services:
       - { name: event_subscriber }
   main_content_renderer.html:
     class: Drupal\Core\Render\MainContent\HtmlRenderer
-    arguments: ['@title_resolver', '@plugin.manager.display_variant', '@event_dispatcher', '@module_handler', '@renderer', '@render_cache']
+    arguments: ['@title_resolver', '@plugin.manager.display_variant', '@event_dispatcher', '@module_handler', '@renderer', '@render_cache', '%renderer.config%']
     tags:
       - { name: render.main_content_renderer, format: html }
   main_content_renderer.ajax:
diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 009bb33e1d9..fd06a1ddead 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -1294,7 +1294,7 @@ function template_preprocess_html(&$variables) {
       '@token' => $token,
     ]);
     $variables[$type]['#markup'] = $placeholder;
-    $variables[$type]['#attached']['html_response_placeholders'][$type] = $placeholder;
+    $variables[$type]['#attached']['html_response_attachment_placeholders'][$type] = $placeholder;
   }
 }
 
diff --git a/core/lib/Drupal/Core/Render/HtmlResponse.php b/core/lib/Drupal/Core/Render/HtmlResponse.php
index c5339d613fa..4447267268c 100644
--- a/core/lib/Drupal/Core/Render/HtmlResponse.php
+++ b/core/lib/Drupal/Core/Render/HtmlResponse.php
@@ -36,12 +36,16 @@ class HtmlResponse extends Response implements CacheableResponseInterface, Attac
     // A render array can automatically be converted to a string and set the
     // necessary metadata.
     if (is_array($content) && (isset($content['#markup']))) {
-      $content += ['#attached' => ['html_response_placeholders' => []]];
+      $content += ['#attached' => [
+        'html_response_attachment_placeholders' => [],
+        'placeholders' => []],
+      ];
       $this->addCacheableDependency(CacheableMetadata::createFromRenderArray($content));
       $this->setAttachments($content['#attached']);
       $content = $content['#markup'];
     }
 
-    parent::setContent($content);
+    return parent::setContent($content);
   }
+
 }
diff --git a/core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php b/core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php
index 0cd74174e4f..cc20063cb1e 100644
--- a/core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php
+++ b/core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php
@@ -99,25 +99,31 @@ class HtmlResponseAttachmentsProcessor implements AttachmentsResponseProcessorIn
       throw new \InvalidArgumentException('\Drupal\Core\Render\HtmlResponse instance expected.');
     }
 
+    // First, render the actual placeholders; this may cause additional
+    // attachments to be added to the response, which the attachment
+    // placeholders rendered by renderHtmlResponseAttachmentPlaceholders() will
+    // need to include.
+    $response = $this->renderPlaceholders($response);
+
     $attached = $response->getAttachments();
 
     // Get the placeholders from attached and then remove them.
-    $placeholders = $attached['html_response_placeholders'];
-    unset($attached['html_response_placeholders']);
+    $attachment_placeholders = $attached['html_response_attachment_placeholders'];
+    unset($attached['html_response_attachment_placeholders']);
 
-    $variables = $this->processAssetLibraries($attached, $placeholders);
+    $variables = $this->processAssetLibraries($attached, $attachment_placeholders);
 
     // Handle all non-asset attachments. This populates drupal_get_html_head().
     $all_attached = ['#attached' => $attached];
     drupal_process_attached($all_attached);
 
     // Get HTML head elements - if present.
-    if (isset($placeholders['head'])) {
+    if (isset($attachment_placeholders['head'])) {
       $variables['head'] = drupal_get_html_head(FALSE);
     }
 
-    // Now replace the placeholders in the response content with the real data.
-    $this->renderPlaceholders($response, $placeholders, $variables);
+    // Now replace the attachment placeholders.
+    $this->renderHtmlResponseAttachmentPlaceholders($response, $attachment_placeholders, $variables);
 
     // Finally set the headers on the response if any bubbled.
     if (!empty($attached['http_header'])) {
@@ -127,6 +133,55 @@ class HtmlResponseAttachmentsProcessor implements AttachmentsResponseProcessorIn
     return $response;
   }
 
+  /**
+   * Renders placeholders (#attached['placeholders']).
+   *
+   * First, the HTML response object is converted to an equivalent render array,
+   * with #markup being set to the response's content and #attached being set to
+   * the response's attachments. Among these attachments, there may be
+   * placeholders that need to be rendered (replaced).
+   *
+   * Next, RendererInterface::renderRoot() is called, which renders the
+   * placeholders into their final markup.
+   *
+   * The markup that results from RendererInterface::renderRoot() is now the
+   * original HTML response's content, but with the placeholders rendered. We
+   * overwrite the existing content in the original HTML response object with
+   * this markup. The markup that was rendered for the placeholders may also
+   * have attachments (e.g. for CSS/JS assets) itself, and cacheability metadata
+   * that indicates what that markup depends on. That metadata is also added to
+   * the HTML response object.
+   *
+   * @param \Drupal\Core\Render\HtmlResponse $response
+   *   The HTML response whose placeholders are being replaced.
+   *
+   * @return \Drupal\Core\Render\HtmlResponse
+   *   The updated HTML response, with replaced placeholders.
+   *
+   * @see \Drupal\Core\Render\Renderer::replacePlaceholders()
+   * @see \Drupal\Core\Render\Renderer::renderPlaceholder()
+   */
+  protected function renderPlaceholders(HtmlResponse $response) {
+    $build = [
+      '#markup' => SafeString::create($response->getContent()),
+      '#attached' => $response->getAttachments(),
+    ];
+    // RendererInterface::renderRoot() renders the $build render array and
+    // updates it in place. We don't care about the return value (which is just
+    // $build['#markup']), but about the resulting render array.
+    // @todo Simplify this when https://www.drupal.org/node/2495001 lands.
+    $this->renderer->renderRoot($build);
+
+    // Update the Response object now that the placeholders have been rendered.
+    $placeholders_bubbleable_metadata = BubbleableMetadata::createFromRenderArray($build);
+    $response
+      ->setContent($build['#markup'])
+      ->addCacheableDependency($placeholders_bubbleable_metadata)
+      ->setAttachments($placeholders_bubbleable_metadata->getAttachments());
+
+    return $response;
+  }
+
   /**
    * Processes asset libraries into render arrays.
    *
@@ -174,8 +229,7 @@ class HtmlResponseAttachmentsProcessor implements AttachmentsResponseProcessorIn
   }
 
   /**
-   * Renders variables into HTML markup and replaces placeholders in the
-   * response content.
+   * Renders HTML response attachment placeholders.
    *
    * @param \Drupal\Core\Render\HtmlResponse $response
    *   The HTML response to update.
@@ -186,7 +240,7 @@ class HtmlResponseAttachmentsProcessor implements AttachmentsResponseProcessorIn
    *   The variables to render and replace, keyed by type with renderable
    *   arrays as values.
    */
-  protected function renderPlaceholders(HtmlResponse $response, array $placeholders, array $variables) {
+  protected function renderHtmlResponseAttachmentPlaceholders(HtmlResponse $response, array $placeholders, array $variables) {
     $content = $response->getContent();
     foreach ($placeholders as $type => $placeholder) {
       if (isset($variables[$type])) {
diff --git a/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php b/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php
index 7e06aabd455..5cfa3121eaa 100644
--- a/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php
+++ b/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php
@@ -8,9 +8,11 @@
 namespace Drupal\Core\Render\MainContent;
 
 use Drupal\Component\Plugin\PluginManagerInterface;
+use Drupal\Core\Cache\Cache;
 use Drupal\Core\Controller\TitleResolverInterface;
 use Drupal\Core\Display\PageVariantInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Core\Render\BubbleableMetadata;
 use Drupal\Core\Render\HtmlResponse;
 use Drupal\Core\Render\PageDisplayVariantSelectionEvent;
 use Drupal\Core\Render\RenderCacheInterface;
@@ -74,6 +76,15 @@ class HtmlRenderer implements MainContentRendererInterface {
    */
   protected $renderCache;
 
+  /**
+   * The renderer configuration array.
+   *
+   * @see sites/default/default.services.yml
+   *
+   * @var array
+   */
+  protected $rendererConfig;
+
   /**
    * Constructs a new HtmlRenderer.
    *
@@ -89,14 +100,17 @@ class HtmlRenderer implements MainContentRendererInterface {
    *   The renderer service.
    * @param \Drupal\Core\Render\RenderCacheInterface $render_cache
    *   The render cache service.
+   * @param array $renderer_config
+   *   The renderer configuration array.
    */
-  public function __construct(TitleResolverInterface $title_resolver, PluginManagerInterface $display_variant_manager, EventDispatcherInterface $event_dispatcher, ModuleHandlerInterface $module_handler, RendererInterface $renderer, RenderCacheInterface $render_cache) {
+  public function __construct(TitleResolverInterface $title_resolver, PluginManagerInterface $display_variant_manager, EventDispatcherInterface $event_dispatcher, ModuleHandlerInterface $module_handler, RendererInterface $renderer, RenderCacheInterface $render_cache, array $renderer_config) {
     $this->titleResolver = $title_resolver;
     $this->displayVariantManager = $display_variant_manager;
     $this->eventDispatcher = $event_dispatcher;
     $this->moduleHandler = $module_handler;
     $this->renderer = $renderer;
     $this->renderCache = $render_cache;
+    $this->rendererConfig = $renderer_config;
   }
 
   /**
@@ -125,11 +139,29 @@ class HtmlRenderer implements MainContentRendererInterface {
     // page.html.twig, hence add them here, just before rendering html.html.twig.
     $this->buildPageTopAndBottom($html);
 
-    // @todo https://www.drupal.org/node/2495001 Make renderRoot return a
-    //       cacheable render array directly.
-    $this->renderer->renderRoot($html);
+    // Render, but don't replace placeholders yet, because that happens later in
+    // the render pipeline. To not replace placeholders yet, we use
+    // RendererInterface::render() instead of RendererInterface::renderRoot().
+    // @see \Drupal\Core\Render\HtmlResponseAttachmentsProcessor.
+    $render_context = new RenderContext();
+    $this->renderer->executeInRenderContext($render_context, function() use (&$html) {
+      // RendererInterface::render() renders the $html render array and updates
+      // it in place. We don't care about the return value (which is just
+      // $html['#markup']), but about the resulting render array.
+      // @todo Simplify this when https://www.drupal.org/node/2495001 lands.
+      $this->renderer->render($html);
+    });
+    // RendererInterface::render() always causes bubbleable metadata to be
+    // stored in the render context, no need to check it conditionally.
+    $bubbleable_metadata = $render_context->pop();
+    $bubbleable_metadata->applyTo($html);
     $content = $this->renderCache->getCacheableRenderArray($html);
 
+    // Also associate the required cache contexts.
+    // (Because we use ::render() above and not ::renderRoot(), we manually must
+    // ensure the HTML response varies by the required cache contexts.)
+    $content['#cache']['contexts'] = Cache::mergeContexts($content['#cache']['contexts'], $this->rendererConfig['required_cache_contexts']);
+
     // Also associate the "rendered" cache tag. This allows us to invalidate the
     // entire render cache, regardless of the cache bin.
     $content['#cache']['tags'][] = 'rendered';