feat: source highlighting for code blocks

package-lock.json

@@ -10,6 +10,7 @@
       "license": "MIT",
       "dependencies": {
         "@floating-ui/dom": "^1.7.5",
+        "@highlightjs/cdn-assets": "^11.11.1",
         "@libsql/client": "^0.17.0",
         "@milkdown/kit": "^7.18.0",
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@@ -750,6 +752,7 @@
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@@ -942,6 +947,7 @@
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@@ -982,6 +988,7 @@
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@@ -1398,7 +1404,6 @@
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@@ -1415,7 +1420,6 @@
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-      "peer": true,
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@@ -2669,6 +2672,15 @@
         "@hapi/hoek": "^11.0.2"
       }
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+      "engines": {
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-      "license": "MIT",
+      "license": "MIT"
-      "peer": true
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+      "peer": true,
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+      "peer": true,
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@@ -6651,6 +6669,7 @@
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       ],
       "license": "MIT",
+      "peer": true,
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-      "optional": true,
+      "optional": true
-      "peer": true
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@@ -7484,7 +7502,8 @@
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@@ -8337,7 +8356,6 @@
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@@ -8385,16 +8402,6 @@
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@@ -8502,6 +8509,7 @@
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+      "peer": true,
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@@ -12340,7 +12350,6 @@
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@@ -12358,7 +12367,6 @@
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@@ -12583,6 +12590,7 @@
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+      "peer": true,
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@@ -12616,6 +12624,7 @@
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+      "peer": true,
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@@ -12693,6 +12702,7 @@
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       "license": "MIT",
+      "peer": true,
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@@ -12758,6 +12768,7 @@
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+      "peer": true,
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@@ -12787,8 +12798,7 @@
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       "dev": true,
-      "license": "MIT",
+      "license": "MIT"
-      "peer": true
     },
     "node_modules/react-refresh": {
       "version": "0.18.0",
@@ -13093,7 +13103,6 @@
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@@ -14116,7 +14124,8 @@
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       "devOptional": true,
-      "license": "0BSD"
+      "license": "0BSD",
+      "peer": true
     },
     "node_modules/tsx": {
       "version": "4.21.0",
@@ -14666,6 +14675,7 @@
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       "devOptional": true,
       "license": "Apache-2.0",
+      "peer": true,
       "bin": {
         "tsc": "bin/tsc",
         "tsserver": "bin/tsserver"
@@ -14955,6 +14965,7 @@
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       "dev": true,
       "license": "MIT",
+      "peer": true,
       "dependencies": {
         "esbuild": "^0.27.0",
         "fdir": "^6.5.0",
@@ -15514,6 +15525,7 @@
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       "dev": true,
       "license": "MIT",
+      "peer": true,
       "dependencies": {
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@@ -15591,6 +15603,7 @@
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       "license": "MIT",
+      "peer": true,
       "dependencies": {
         "@vue/compiler-dom": "3.5.28",
         "@vue/compiler-sfc": "3.5.28",

package.json

@@ -61,6 +61,7 @@
   },
   "dependencies": {
     "@floating-ui/dom": "^1.7.5",
+    "@highlightjs/cdn-assets": "^11.11.1",
     "@libsql/client": "^0.17.0",
     "@milkdown/kit": "^7.18.0",
     "@milkdown/plugin-block": "^7.18.0",

src/main/engine/BlogGenerationEngine.ts

@@ -307,6 +307,8 @@ export class BlogGenerationEngine {
     let sitemapWritten = false;
     let rssWritten = false;
     let atomWritten = false;
+    const generatedHashCache = new Map<string, string | null>();
+    const knownOutputDirectories = new Set<string>();
 
     if (includeCore) {
       onProgress(10, 'Writing sitemap and feeds...');
@@ -333,7 +335,10 @@ export class BlogGenerationEngine {
       reportUnitProgress('Atom feed written');
 
       onProgress(15, 'Copying assets...');
-      await copyPreviewAssets(htmlDir);
+      await copyPreviewAssets(htmlDir, {
+        projectId: options.projectId,
+        hashCache: generatedHashCache,
+      });
       reportUnitProgress('Assets copied');
     }
 
@@ -348,9 +353,6 @@ export class BlogGenerationEngine {
       },
     });
 
-    const knownOutputDirectories = new Set<string>();
-    const generatedHashCache = new Map<string, string | null>();
-
     const writePage = (projectId: string, urlPath: string, content: string) => writeHtmlPage({
       projectId,
       htmlDir,

src/main/engine/BlogGenerationOutputService.ts

@@ -4,6 +4,25 @@ import * as path from 'node:path';
 import { getGeneratedFileHash, setGeneratedFileHash } from '../database/generatedFileHashStore';
 import { PREVIEW_ASSETS, PREVIEW_IMAGE_ASSETS } from './PageRenderer';
 
+type PreviewAssetMap = Record<string, { contentType: string; modulePath?: string; sourceText?: string }>;
+type PreviewImageAssetMap = Record<string, { modulePath: string; contentType: string }>;
+
+function toBuffer(value: unknown): Buffer {
+  if (Buffer.isBuffer(value)) {
+    return value;
+  }
+
+  if (typeof value === 'string') {
+    return Buffer.from(value, 'utf-8');
+  }
+
+  if (value instanceof Uint8Array) {
+    return Buffer.from(value);
+  }
+
+  return Buffer.alloc(0);
+}
+
 export function normalizeGeneratedUrlPath(urlPath: string): string {
   const trimmed = (urlPath || '').trim();
   if (!trimmed || trimmed === '/') {
@@ -28,6 +47,10 @@ export function computeContentHash(content: string): string {
   return crypto.createHash('sha256').update(content).digest('hex');
 }
 
+export function computeBufferHash(content: Buffer): string {
+  return crypto.createHash('sha256').update(content).digest('hex');
+}
+
 export async function writeFileIfHashChanged(params: {
   projectId: string;
   filePath: string;
@@ -104,24 +127,67 @@ export async function writeHtmlPage(params: {
   });
 }
 
-export async function copyPreviewAssets(htmlDir: string): Promise<void> {
+export async function copyPreviewAssets(htmlDir: string, options?: {
+  projectId?: string;
+  hashCache?: Map<string, string | null>;
+  previewAssets?: PreviewAssetMap;
+  previewImageAssets?: PreviewImageAssetMap;
+  readModuleFile?: (modulePath: string) => Promise<Buffer>;
+  getGeneratedFileHash?: (projectId: string, relativePath: string) => Promise<string | null>;
+  setGeneratedFileHash?: (projectId: string, relativePath: string, hash: string) => Promise<void>;
+}): Promise<void> {
   const assetsDir = path.join(htmlDir, 'assets');
   const imagesDir = path.join(htmlDir, 'images');
   await fs.mkdir(assetsDir, { recursive: true });
   await fs.mkdir(imagesDir, { recursive: true });
 
-  for (const [filename, definition] of Object.entries(PREVIEW_ASSETS)) {
+  const projectId = options?.projectId;
-    const destPath = path.join(assetsDir, filename);
+  const hashCache = options?.hashCache;
-    const content = definition.sourceText !== undefined
+  const readModuleFile = options?.readModuleFile ?? (async (modulePath: string) => toBuffer(await fs.readFile(require.resolve(modulePath))));
-      ? Buffer.from(definition.sourceText, 'utf-8')
+  const getHash = options?.getGeneratedFileHash ?? getGeneratedFileHash;
-      : await fs.readFile(require.resolve(definition.modulePath as string));
+  const setHash = options?.setGeneratedFileHash ?? setGeneratedFileHash;
-    await fs.writeFile(destPath, content);
+  const previewAssets = options?.previewAssets ?? PREVIEW_ASSETS;
+  const previewImageAssets = options?.previewImageAssets ?? PREVIEW_IMAGE_ASSETS;
+
+  const writeBinaryIfHashChanged = async (filePath: string, relativePath: string, content: Buffer): Promise<void> => {
+    if (!projectId) {
+      await fs.writeFile(filePath, content);
+      return;
     }
 
-  for (const [filename, definition] of Object.entries(PREVIEW_IMAGE_ASSETS)) {
+    const hash = computeBufferHash(content);
-    const sourcePath = require.resolve(definition.modulePath);
+    let previousHash: string | null;
+    if (hashCache && hashCache.has(relativePath)) {
+      previousHash = hashCache.get(relativePath) ?? null;
+    } else {
+      previousHash = await getHash(projectId, relativePath);
+      hashCache?.set(relativePath, previousHash);
+    }
+
+    if (previousHash === hash) {
+      return;
+    }
+
+    await fs.writeFile(filePath, content);
+    await setHash(projectId, relativePath, hash);
+    hashCache?.set(relativePath, hash);
+  };
+
+  for (const [filename, definition] of Object.entries(previewAssets)) {
+    const destPath = path.join(assetsDir, filename);
+    const relativePath = path.posix.join('assets', filename);
+    const content = definition.sourceText !== undefined
+      ? Buffer.from(definition.sourceText, 'utf-8')
+      : toBuffer(await readModuleFile(definition.modulePath as string));
+
+    await writeBinaryIfHashChanged(destPath, relativePath, content);
+  }
+
+  for (const [filename, definition] of Object.entries(previewImageAssets)) {
     const destPath = path.join(imagesDir, filename);
-    const content = await fs.readFile(sourcePath);
+    const relativePath = path.posix.join('images', filename);
-    await fs.writeFile(destPath, content);
+    const content = toBuffer(await readModuleFile(definition.modulePath));
+
+    await writeBinaryIfHashChanged(destPath, relativePath, content);
   }
 }

src/main/engine/PageRenderer.ts

@@ -5,6 +5,7 @@ import type { MediaData } from './MediaEngine';
 import type { PostData } from './PostEngine';
 import type { MenuDocument, MenuItemData } from './MenuEngine';
 import { PICO_THEME_NAMES } from '../shared/picoThemes';
+import { CODE_ENHANCEMENTS_RUNTIME_JS } from './assets/codeEnhancementsRuntime';
 import { TAG_CLOUD_RUNTIME_JS } from './assets/tagCloudRuntime';
 import { resolveRenderLanguageFromProjectPreferences, translateRender } from '../shared/i18n';
 
@@ -135,6 +136,29 @@ export interface PreviewAssetDefinition {
   sourceText?: string;
 }
 
+function annotateCodeBlocksWithLanguage(html: string): string {
+  if (!html) {
+    return html;
+  }
+
+  return html.replace(/<code\b([^>]*)>/gi, (fullMatch, rawAttributes: string) => {
+    if (/\bdata-code-language\s*=/.test(rawAttributes)) {
+      return fullMatch;
+    }
+
+    const classMatch = rawAttributes.match(/\bclass\s*=\s*"([^"]*)"/i);
+    const classList = classMatch?.[1] ?? '';
+    const languageMatch = classList.match(/(?:^|\s)language-([\w.+-]+)(?:\s|$)/i);
+    const language = languageMatch?.[1]?.toLowerCase();
+
+    if (!language) {
+      return fullMatch;
+    }
+
+    return `<code${rawAttributes} data-code-language="${escapeHtml(language)}">`;
+  });
+}
+
 export interface TagUsageEntry {
   tag: string;
   count: number;
@@ -178,6 +202,18 @@ export const PREVIEW_ASSETS: Record<string, PreviewAssetDefinition> = {
     modulePath: 'lightbox2/dist/js/lightbox-plus-jquery.min.js',
     contentType: 'application/javascript; charset=utf-8',
   },
+  'highlight.min.css': {
+    modulePath: '@highlightjs/cdn-assets/styles/github-dark.min.css',
+    contentType: 'text/css; charset=utf-8',
+  },
+  'highlight.min.js': {
+    modulePath: '@highlightjs/cdn-assets/highlight.min.js',
+    contentType: 'application/javascript; charset=utf-8',
+  },
+  'code-enhancements.js': {
+    contentType: 'application/javascript; charset=utf-8',
+    sourceText: CODE_ENHANCEMENTS_RUNTIME_JS,
+  },
   'd3.layout.cloud.js': {
     modulePath: 'd3-cloud/build/d3.layout.cloud.js',
     contentType: 'application/javascript; charset=utf-8',
@@ -829,7 +865,8 @@ export class PageRenderer {
       });
 
       const markdownHtml = await marked.parse(withMacros, { async: true, gfm: true, breaks: false });
-      return rewriteRenderedHtmlUrls(markdownHtml, rewriteContext);
+      const annotatedMarkdownHtml = annotateCodeBlocksWithLanguage(markdownHtml);
+      return rewriteRenderedHtmlUrls(annotatedMarkdownHtml, rewriteContext);
     });
   }
 

src/main/engine/assets/codeEnhancementsRuntime.ts

@@ -0,0 +1,137 @@
+export const CODE_ENHANCEMENTS_RUNTIME_JS = String.raw`(function () {
+  function resolveCodeLanguage(codeElement) {
+    if (!codeElement) {
+      return '';
+    }
+
+    var direct = codeElement.getAttribute('data-code-language');
+    if (typeof direct === 'string' && direct.trim()) {
+      return direct.trim().toLowerCase();
+    }
+
+    var className = codeElement.className || '';
+    var classMatch = className.match(/(?:^|\s)language-([\w.+-]+)/i);
+    if (classMatch && classMatch[1]) {
+      return classMatch[1].toLowerCase();
+    }
+
+    return '';
+  }
+
+  function fallbackCopy(value) {
+    var textarea = document.createElement('textarea');
+    textarea.value = value;
+    textarea.setAttribute('readonly', 'readonly');
+    textarea.style.position = 'fixed';
+    textarea.style.opacity = '0';
+    textarea.style.pointerEvents = 'none';
+    document.body.appendChild(textarea);
+    textarea.focus();
+    textarea.select();
+
+    try {
+      return document.execCommand('copy');
+    } catch {
+      return false;
+    } finally {
+      document.body.removeChild(textarea);
+    }
+  }
+
+  async function copyCodeToClipboard(value) {
+    if (navigator.clipboard && typeof navigator.clipboard.writeText === 'function') {
+      try {
+        await navigator.clipboard.writeText(value);
+        return true;
+      } catch {
+        return fallbackCopy(value);
+      }
+    }
+
+    return fallbackCopy(value);
+  }
+
+  function ensureCopyButton(preElement, codeElement) {
+    if (!preElement || preElement.querySelector(':scope > .code-copy-button')) {
+      return;
+    }
+
+    preElement.classList.add('code-block-enhanced');
+
+    var button = document.createElement('button');
+    button.type = 'button';
+    button.className = 'code-copy-button';
+    button.setAttribute('aria-hidden', 'true');
+
+    var icon = document.createElement('span');
+    icon.className = 'code-copy-icon';
+    icon.textContent = '⧉';
+    button.appendChild(icon);
+
+    button.addEventListener('click', async function () {
+      var codeText = codeElement.textContent || '';
+      var copied = await copyCodeToClipboard(codeText);
+      preElement.classList.remove('code-copy-failed');
+      preElement.classList.remove('code-copy-success');
+      preElement.classList.add(copied ? 'code-copy-success' : 'code-copy-failed');
+
+      if (copied) {
+        icon.textContent = '✓';
+        window.setTimeout(function () {
+          preElement.classList.remove('code-copy-success');
+          icon.textContent = '⧉';
+        }, 1200);
+        return;
+      }
+
+      window.setTimeout(function () {
+        preElement.classList.remove('code-copy-failed');
+      }, 1200);
+    });
+
+    preElement.appendChild(button);
+  }
+
+  function highlightCodeBlock(codeElement) {
+    var highlighter = window.hljs;
+    if (!highlighter || typeof highlighter.highlightElement !== 'function') {
+      return;
+    }
+
+    if (codeElement.getAttribute('data-code-highlighted') === 'true') {
+      return;
+    }
+
+    try {
+      highlighter.highlightElement(codeElement);
+      codeElement.setAttribute('data-code-highlighted', 'true');
+    } catch {
+    }
+  }
+
+  function initCodeBlocks() {
+    var codeNodes = document.querySelectorAll('pre > code');
+    codeNodes.forEach(function (codeElement) {
+      var preElement = codeElement.parentElement;
+      if (!preElement || preElement.tagName !== 'PRE') {
+        return;
+      }
+
+      var language = resolveCodeLanguage(codeElement);
+      if (language) {
+        codeElement.setAttribute('data-code-language', language);
+        preElement.setAttribute('data-code-language', language);
+      }
+
+      ensureCopyButton(preElement, codeElement);
+      highlightCodeBlock(codeElement);
+    });
+  }
+
+  if (document.readyState === 'loading') {
+    document.addEventListener('DOMContentLoaded', initCodeBlocks, { once: true });
+  } else {
+    initCodeBlocks();
+  }
+})();
+`;

src/main/engine/templates/partials/head.liquid

@@ -5,9 +5,12 @@
   {% assign resolved_pico_stylesheet_href = pico_stylesheet_href | default: '/assets/pico.min.css' %}
   <link rel="stylesheet" href="{{ resolved_pico_stylesheet_href }}" />
   <link rel="stylesheet" href="/assets/lightbox.min.css" />
+  <link rel="stylesheet" href="/assets/highlight.min.css" />
   <link rel="alternate" type="application/rss+xml" title="RSS" href="/rss.xml" />
   <link rel="alternate" type="application/atom+xml" title="Atom" href="/atom.xml" />
   {% render 'partials/styles' %}
+  <script defer src="/assets/highlight.min.js"></script>
+  <script defer src="/assets/code-enhancements.js"></script>
   <script defer src="/assets/d3.layout.cloud.js"></script>
   <script defer src="/assets/tag-cloud.js"></script>
   <script defer src="/assets/lightbox.min.js"></script>

src/main/engine/templates/partials/styles.liquid

@@ -18,6 +18,30 @@
   .blog-menu-item-with-children:hover > .blog-menu-submenu,
   .blog-menu-item-with-children:focus-within > .blog-menu-submenu { display: block; }
   .post { border: 1px solid var(--pico-muted-border-color, var(--muted-border-color)); padding: 1rem; background: var(--pico-card-background-color, var(--card-background-color)); }
+  .post pre { position: relative; overflow-x: auto; border: 1px solid var(--pico-muted-border-color, var(--muted-border-color)); border-radius: .3rem; margin: .9rem 0; padding: .85rem .9rem; background: var(--pico-code-background-color, rgba(33, 38, 45, .82)); }
+  .post pre code { display: block; font-size: .88rem; line-height: 1.5; }
+  .code-copy-button {
+    position: absolute;
+    top: .4rem;
+    right: .4rem;
+    border: 1px solid var(--pico-muted-border-color, var(--muted-border-color));
+    background: var(--pico-card-background-color, var(--card-background-color));
+    color: var(--pico-muted-color, var(--muted-color));
+    border-radius: .25rem;
+    width: 1.8rem;
+    height: 1.8rem;
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    padding: 0;
+    cursor: pointer;
+    opacity: .88;
+  }
+  .code-copy-button:hover,
+  .code-copy-button:focus-visible { opacity: 1; color: var(--pico-color, var(--color)); }
+  .code-copy-icon { font-size: .95rem; line-height: 1; }
+  .code-copy-success .code-copy-button { color: var(--pico-ins-color, rgb(53, 117, 56)); border-color: var(--pico-ins-color, rgb(53, 117, 56)); }
+  .code-copy-failed .code-copy-button { color: var(--pico-del-color, rgb(183, 72, 72)); border-color: var(--pico-del-color, rgb(183, 72, 72)); }
   .post iframe { width: 100%; min-height: 20rem; }
   .macro-gallery, .macro-photo-archive, .macro-tag-cloud { border: 1px dashed var(--pico-muted-border-color, var(--muted-border-color)); padding: .75rem; margin: 1rem 0; }
   .gallery-container { display: grid; gap: .5rem; }

tests/engine/BlogGenerationOutputService.test.ts

@@ -2,6 +2,7 @@ import { mkdir, readFile } from 'node:fs/promises';
 import path from 'node:path';
 import { describe, expect, it, vi } from 'vitest';
 import {
+  copyPreviewAssets,
   normalizeGeneratedUrlPath,
   urlPathToHtmlIndexPath,
   writeFileIfHashChanged,
@@ -145,4 +146,73 @@ describe('BlogGenerationOutputService', () => {
 
     expect(ensureDirectory).toHaveBeenCalledTimes(1);
   });
+
+  it('copies preview assets with hash checks so unchanged files are not rewritten', async () => {
+    const tempRoot = path.join('/tmp', makeTempName());
+    const htmlDir = path.join(tempRoot, 'html');
+    await mkdir(htmlDir, { recursive: true });
+
+    const hashStore = new Map<string, string>();
+    const getHash = vi.fn(async (_projectId: string, relativePath: string) => hashStore.get(relativePath) ?? null);
+    const setHash = vi.fn(async (_projectId: string, relativePath: string, hash: string) => {
+      hashStore.set(relativePath, hash);
+    });
+
+    const hashCache = new Map<string, string | null>();
+
+    await copyPreviewAssets(htmlDir, {
+      projectId: 'project-a',
+      hashCache,
+      previewAssets: {
+        'runtime.js': {
+          contentType: 'application/javascript; charset=utf-8',
+          sourceText: 'console.log("runtime");',
+        },
+      },
+      previewImageAssets: {
+        'pixel.png': {
+          modulePath: 'virtual:pixel.png',
+          contentType: 'image/png',
+        },
+      },
+      readModuleFile: async (modulePath: string) => {
+        if (modulePath === 'virtual:pixel.png') {
+          return Buffer.from([0, 1, 2, 3]);
+        }
+        throw new Error(`Unexpected module path: ${modulePath}`);
+      },
+      getGeneratedFileHash: getHash,
+      setGeneratedFileHash: setHash,
+    });
+
+    await copyPreviewAssets(htmlDir, {
+      projectId: 'project-a',
+      hashCache,
+      previewAssets: {
+        'runtime.js': {
+          contentType: 'application/javascript; charset=utf-8',
+          sourceText: 'console.log("runtime");',
+        },
+      },
+      previewImageAssets: {
+        'pixel.png': {
+          modulePath: 'virtual:pixel.png',
+          contentType: 'image/png',
+        },
+      },
+      readModuleFile: async (modulePath: string) => {
+        if (modulePath === 'virtual:pixel.png') {
+          return Buffer.from([0, 1, 2, 3]);
+        }
+        throw new Error(`Unexpected module path: ${modulePath}`);
+      },
+      getGeneratedFileHash: getHash,
+      setGeneratedFileHash: setHash,
+    });
+
+    expect(setHash).toHaveBeenCalledTimes(2);
+    expect(await readFile(path.join(htmlDir, 'assets', 'runtime.js'), 'utf-8')).toBe('console.log("runtime");');
+    const imageContent = await readFile(path.join(htmlDir, 'images', 'pixel.png'));
+    expect(Array.from(imageContent)).toEqual([0, 1, 2, 3]);
+  });
 });

tests/engine/PreviewServer.test.ts

@@ -304,7 +304,10 @@ describe('PreviewServer', () => {
 
     expect(rootHtml).toContain('href="/assets/pico.min.css"');
     expect(rootHtml).toContain('href="/assets/lightbox.min.css"');
+    expect(rootHtml).toContain('href="/assets/highlight.min.css"');
     expect(rootHtml).toContain('src="/assets/lightbox.min.js"');
+    expect(rootHtml).toContain('src="/assets/highlight.min.js"');
+    expect(rootHtml).toContain('src="/assets/code-enhancements.js"');
     expect(rootHtml).toContain('src="/assets/d3.layout.cloud.js"');
     expect(rootHtml).toContain('src="/assets/tag-cloud.js"');
     expect(rootHtml).not.toContain('function parseWords(');
@@ -322,6 +325,18 @@ describe('PreviewServer', () => {
     expect(lightboxJsResponse.status).toBe(200);
     expect(lightboxJsResponse.headers.get('content-type')).toContain('application/javascript');
 
+    const highlightCssResponse = await fetch(`${server.getBaseUrl()}/assets/highlight.min.css`);
+    expect(highlightCssResponse.status).toBe(200);
+    expect(highlightCssResponse.headers.get('content-type')).toContain('text/css');
+
+    const highlightJsResponse = await fetch(`${server.getBaseUrl()}/assets/highlight.min.js`);
+    expect(highlightJsResponse.status).toBe(200);
+    expect(highlightJsResponse.headers.get('content-type')).toContain('application/javascript');
+
+    const codeEnhancementsResponse = await fetch(`${server.getBaseUrl()}/assets/code-enhancements.js`);
+    expect(codeEnhancementsResponse.status).toBe(200);
+    expect(codeEnhancementsResponse.headers.get('content-type')).toContain('application/javascript');
+
     const d3CloudJsResponse = await fetch(`${server.getBaseUrl()}/assets/d3.layout.cloud.js`);
     expect(d3CloudJsResponse.status).toBe(200);
     expect(d3CloudJsResponse.headers.get('content-type')).toContain('application/javascript');
@@ -339,6 +354,23 @@ describe('PreviewServer', () => {
     expect(lightboxLoadingImageResponse.headers.get('content-type')).toContain('image/gif');
   });
 
+  it('keeps markdown code block html minimal and includes code language metadata', async () => {
+    const postWithCode = makePost({
+      content: '```python\nprint("hello")\n```',
+    });
+
+    server = new PreviewServer({
+      postEngine: makeEngine([postWithCode]),
+      settingsEngine: makeSettings(50),
+      getActiveProjectContext: async () => ({ projectId: 'default' }),
+    });
+
+    await server.start(0);
+
+    const html = await (await fetch(`${server.getBaseUrl()}/`)).text();
+    expect(html).toContain('<code class="language-python" data-code-language="python">');
+  });
+
   it('does not set project context or run startup sync for static asset requests', async () => {
     const postEngine = makeEngine([makePost()]);
     const mediaEngine = {