Merge pull request 'Show the pictures inside Reddit comments' (#5) from reddit-inline-images into main

Reviewed-on: #5

CLAUDE.md

@@ -147,7 +147,16 @@ Things worth knowing before editing:
   timeline thumbnails, and the still is in `preview.images`. A gallery's pictures are in
   `media_metadata`, keyed and unordered; their order is only in `gallery_data`. Comment
   bodies are Markdown, rendered by `src/render/markdown.ts` — escape first, then put
-  back the constructs we chose to support, never `body_html`.
+  back the constructs we chose to support, never `body_html`. An image in a comment is
+  written as a token rather than an address — `![gif](giphy|Ve7wX45)`,
+  `![img](emote|t5_2th52|4358)`, `![img](jo8gf0ca92zd1)` — and in every case the token is
+  a key in that same comment's own `media_metadata`, so `resolveInlineImages` is one
+  lookup rather than three special cases. A bare `preview.redd.it` address pasted into a
+  comment is in there too, keyed by the id inside the URL. Prefer `s.gif` over `s.mp4`
+  for an animated one: a GIF moves in an `<img>` and an MP4 needs a player. An address
+  typed without a scheme counts as well, but only when it ends in an image extension —
+  the rule wants a host, a path *and* that extension, because comments are full of
+  dotted, slashed prose that must not turn into links.
 - **Threads** — same media schema as Instagram (`src/platforms/meta-media.ts`). Its
   payloads are full of empty stub nodes, so the finder only accepts a node with actual
   candidates in it. The page ships the linked post, the author's follow-ups, other

README.md

@@ -126,6 +126,13 @@ which is why it only appears once the script has run. What was behind a _load mo
 not fetched — that is a second page and often a third — but it is counted and said out
 loud rather than quietly dropped.
 
+Pictures inside comments are shown as pictures. Reddit writes them as a token rather
+than an address — a Giphy id, a subreddit emote, or an image uploaded to the comment —
+and all three are looked up in the comment's own metadata to find the real file. An
+image address someone simply pasted is shown too, which on Reddit is how most of them
+arrive. All of it goes through the same `/m/` proxy as everything else, so reading a
+comment thread never has your browser talking to Reddit.
+
 Media never gets linked straight at a CDN. Instagram and TikTok reject requests without
 a matching `Referer` (and sometimes cookies), and proxying keeps your browser from
 talking to the platform at all. Every asset is registered under an opaque `/m/<id>` and

public/app.css

@@ -556,3 +556,22 @@ main { max-width: 680px; margin: 0 auto; }
   max-height: 45dvh;
   min-height: 0;
 }
+
+/* A picture someone put in a comment. Capped hard: it is a remark inside a
+   conversation, not the thing the page is about. */
+.c__img {
+  display: block;
+  max-width: min(100%, 420px);
+  max-height: 40vh;
+  max-height: 40dvh;
+  width: auto;
+  height: auto;
+  margin: 8px 0;
+  border: 1px solid var(--line);
+  border-radius: 8px;
+  background: color-mix(in srgb, var(--ink) 4%, transparent);
+}
+
+/* A lone image is the whole comment more often than not, so it should not
+   carry a paragraph's worth of space above it as well as its own. */
+.c__body > p:first-child > .c__img:first-child { margin-top: 2px; }

src/platforms/reddit.ts

@@ -62,6 +62,7 @@ type Link = {
 type CommentData = {
   author?: string;
   body?: string;
+  media_metadata?: Record<string, MediaMeta>;
   created_utc?: number;
   score?: number;
   score_hidden?: boolean;
@@ -188,6 +189,37 @@ function bodyOf(link: Link): string | undefined {
   return undefined;
 }
 
+/** The whole of `![...](...)`, with the target captured. */
+const INLINE_IMAGE = /!\[([^\]\n]*)\]\(([^)\s]+)\)/g;
+
+/**
+ * Point a comment's inline images at something fetchable.
+ *
+ * Reddit writes them as `![gif](giphy|Ve7wX45)`, `![img](emote|t5_2th52|4358)`
+ * or `![img](jo8gf0ca92zd1)` — a token rather than an address. In every case
+ * the token is a key in that same comment's `media_metadata`, which is where
+ * the real URL is, so one lookup covers all three and none of them needs
+ * naming here.
+ *
+ * A target that is already an address is not a key, so it falls through
+ * untouched.
+ */
+export function resolveInlineImages(
+  body: string,
+  meta: Record<string, MediaMeta> | undefined,
+): string {
+  if (!meta) return body;
+
+  return body.replace(INLINE_IMAGE, (whole, alt: string, token: string) => {
+    const entry = meta[token];
+    if (!entry || entry.status !== 'valid') return whole;
+    // An animated one has both; the GIF plays in an `<img>` on its own, which
+    // an MP4 does not.
+    const url = entry.s?.gif ?? entry.s?.u;
+    return url ? `![${alt}](${url})` : whole;
+  });
+}
+
 export function commentsFrom(listing: Listing<CommentData> | undefined): {
   comments: Comment[];
   more: number;
@@ -209,7 +241,7 @@ export function commentsFrom(listing: Listing<CommentData> | undefined): {
 
     comments.push({
       author: authorName(data.author),
-      ...(data.body ? { text: data.body } : {}),
+      ...(data.body ? { text: resolveInlineImages(data.body, data.media_metadata) } : {}),
       ...(isoFrom(data.created_utc) ? { postedAt: isoFrom(data.created_utc) } : {}),
       // Reddit hides the score on a new comment so an early downvote cannot
       // steer the rest. Showing a placeholder 1 would be a lie.

src/render/markdown.ts

@@ -13,6 +13,20 @@ import { escapeHtml, raw, type Raw } from './html.ts';
 
 const REDDIT = 'https://www.reddit.com';
 
+/**
+ * How an image in a comment becomes markup.
+ *
+ * Supplied by the caller rather than decided here, because the address has to
+ * go through the media proxy and this file knows nothing about that. Without
+ * one an image degrades to a link, which is what it was before.
+ */
+export type ImageRenderer = (url: string, alt: string) => string;
+
+/** Worth showing as a picture rather than as a link to one. */
+function looksLikeImage(url: string): boolean {
+  return /\.(jpe?g|png|gif|webp|avif)(\?|$)/i.test(url);
+}
+
 /** Absolute http(s) only. `javascript:` and friends never become links. */
 function safeHref(url: string): string | undefined {
   try {
@@ -46,44 +60,69 @@ function trimUrlTail(url: string): string {
 const INLINE = new RegExp(
   [
     '`([^`\\n]+)`', // 1 code
-    '\\[([^\\]\\n]+)\\]\\(([^)\\s]+)\\)', // 2 label, 3 href
+    // Before the link rule, or the `[` of an image matches as a link and
-    '\\*\\*([^*\\n]+)\\*\\*', // 4 strong
+    // leaves its `!` behind as text.
-    '~~([^~\\n]+)~~', // 5 strike
+    '!\\[([^\\]\\n]*)\\]\\(([^)\\s]+)\\)', // 2 alt, 3 src
-    '(?<![\\w*])\\*([^*\\n]+)\\*(?![\\w*])', // 6 em with asterisks
+    '\\[([^\\]\\n]+)\\]\\(([^)\\s]+)\\)', // 4 label, 5 href
-    '(?<![\\w_])_([^_\\n]+)_(?![\\w_])', // 7 em with underscores
+    '\\*\\*([^*\\n]+)\\*\\*', // 6 strong
-    '(https?://[^\\s<>]+)', // 8 bare url
+    '~~([^~\\n]+)~~', // 7 strike
-    '(?<![\\w/])(/?[ru]/[A-Za-z0-9_][A-Za-z0-9_-]{1,30})', // 9 r/sub and u/name
+    '(?<![\\w*])\\*([^*\\n]+)\\*(?![\\w*])', // 8 em with asterisks
+    '(?<![\\w_])_([^_\\n]+)_(?![\\w_])', // 9 em with underscores
+    '(https?://[^\\s<>]+)', // 10 bare url
+    // 11 the same thing with the scheme left off, which is how people type
+    // them. Narrow on purpose: a host, a path, and an image extension. Prose
+    // is full of dotted words, and `src/render/post.ts` must not become a
+    // link to a website in Tonga.
+    '(?<![\\w@/.])((?:[a-z0-9-]+\\.)+[a-z]{2,}/[^\\s<>]*\\.(?:jpe?g|png|gif|webp|avif)(?:\\?[^\\s<>]*)?)',
+    '(?<![\\w/])(/?[ru]/[A-Za-z0-9_][A-Za-z0-9_-]{1,30})', // 12 r/sub and u/name
   ].join('|'),
   'g',
 );
 
 /** One line of body text: escaped, with the inline constructs put back. */
-function inline(text: string): string {
+function inline(text: string, image?: ImageRenderer): string {
   let out = '';
   let cursor = 0;
 
   for (const match of text.matchAll(INLINE)) {
-    const [whole, code, label, href, strong, strike, emStar, emScore, url, subOrUser] = match;
+    const [whole, code, alt, src, label, href, strong, strike, emStar, emScore, url, schemeless,
+      subOrUser] = match;
     out += escapeHtml(text.slice(cursor, match.index));
     cursor = match.index + whole.length;
 
     if (code !== undefined) {
       out += `<code>${escapeHtml(code)}</code>`;
+    } else if (src !== undefined) {
+      const safe = safeHref(src);
+      // Without a renderer to place it, an image is still a link to one.
+      out += safe ? (image ? image(safe, alt ?? '') : anchor(safe, alt || safe)) : escapeHtml(whole);
     } else if (label !== undefined && href !== undefined) {
       const safe = safeHref(href);
       out += safe ? anchor(safe, label) : escapeHtml(whole);
     } else if (strong !== undefined) {
-      out += `<strong>${inline(strong)}</strong>`;
+      out += `<strong>${inline(strong, image)}</strong>`;
     } else if (strike !== undefined) {
-      out += `<del>${inline(strike)}</del>`;
+      out += `<del>${inline(strike, image)}</del>`;
     } else if (emStar !== undefined || emScore !== undefined) {
-      out += `<em>${inline(emStar ?? emScore ?? '')}</em>`;
+      out += `<em>${inline(emStar ?? emScore ?? '', image)}</em>`;
     } else if (url !== undefined) {
       const trimmed = trimUrlTail(url);
       const safe = safeHref(trimmed);
-      out += safe
+      const tail = escapeHtml(url.slice(trimmed.length));
-        ? anchor(safe, trimmed.replace(/^https?:\/\/(www\.)?/, '')) + escapeHtml(url.slice(trimmed.length))
+      if (!safe) {
-        : escapeHtml(whole);
+        out += escapeHtml(whole);
+      } else if (image && looksLikeImage(trimmed)) {
+        // People paste the address of a picture and mean the picture. On
+        // Reddit that is most of what an image in a comment even is.
+        out += image(safe, '') + tail;
+      } else {
+        out += anchor(safe, trimmed.replace(/^https?:\/\/(www\.)?/, '')) + tail;
+      }
+    } else if (schemeless !== undefined) {
+      // Assumed https: every host that serves these redirects to it anyway,
+      // and a picture is the one thing worth guessing a scheme for.
+      const safe = safeHref(`https://${schemeless}`);
+      out += safe ? (image ? image(safe, '') : anchor(safe, schemeless)) : escapeHtml(whole);
     } else if (subOrUser !== undefined) {
       const path = subOrUser.startsWith('/') ? subOrUser : `/${subOrUser}`;
       out += anchor(`${REDDIT}${path}`, subOrUser);
@@ -101,7 +140,7 @@ const NUMBERED = /^\s{0,3}\d+[.)]\s+/;
  * from the reply to it, and a comment that loses that separation reads as
  * though the commenter said both halves.
  */
-function blocks(lines: string[]): string {
+function blocks(lines: string[], image?: ImageRenderer): string {
   let out = '';
   let at = 0;
 
@@ -139,7 +178,7 @@ function blocks(lines: string[]): string {
     if (/^\s*>/.test(line)) {
       const body = takeWhile((l) => /^\s*>/.test(l));
       // Nested, so a quote of a quote keeps its shape.
-      out += `<blockquote>${blocks(body.map((l) => l.replace(/^\s*>\s?/, '')))}</blockquote>`;
+      out += `<blockquote>${blocks(body.map((l) => l.replace(/^\s*>\s?/, '')), image)}</blockquote>`;
       continue;
     }
 
@@ -148,20 +187,21 @@ function blocks(lines: string[]): string {
       const pattern = ordered ? NUMBERED : BULLET;
       const items = takeWhile((l) => pattern.test(l));
       const tag = ordered ? 'ol' : 'ul';
-      out += `<${tag}>${items.map((l) => `<li>${inline(l.replace(pattern, ''))}</li>`).join('')}</${tag}>`;
+      out += `<${tag}>${items.map((l) => `<li>${inline(l.replace(pattern, ''), image)}</li>`).join('')}</${tag}>`;
       continue;
     }
 
     const paragraph = takeWhile(
       (l) => l.trim() !== '' && !/^\s*>/.test(l) && !BULLET.test(l) && !NUMBERED.test(l) && !/^\s*```/.test(l),
     );
-    out += `<p>${paragraph.map((l) => inline(l)).join('<br>')}</p>`;
+    out += `<p>${paragraph.map((l) => inline(l, image)).join('<br>')}</p>`;
   }
 
   return out;
 }
 
-/** Comment text, as safe markup. */
+/** Comment text, as safe markup. `image` places the pictures; without it
-export function renderMarkdown(text: string): Raw {
+ *  they stay links, which is what they were before. */
-  return raw(blocks(text.replace(/\r\n?/g, '\n').split('\n')));
+export function renderMarkdown(text: string, image?: ImageRenderer): Raw {
+  return raw(blocks(text.replace(/\r\n?/g, '\n').split('\n'), image));
 }

src/render/post.ts

@@ -145,6 +145,22 @@ function shortWhen(postedAt: string | undefined): Raw {
   })}</time>`;
 }
 
+/**
+ * A picture inside a comment.
+ *
+ * Through the proxy like everything else — a comment full of `preview.redd.it`
+ * addresses would otherwise have the viewer's browser fetch every one of them
+ * straight from Reddit, which is the thing this whole app exists to avoid.
+ *
+ * No dimensions to reserve space with: the size is in the payload but not in
+ * the Markdown, so these are capped by the stylesheet and load at whatever
+ * shape they are.
+ */
+function renderCommentImage(url: string, alt: string): string {
+  return html`<img class="c__img" src="${proxyUrlFor({ url })}" alt="${alt}" loading="lazy" decoding="async">`
+    .value;
+}
+
 /** Everything hanging off a comment, however deep. Shown only while it is
  *  collapsed, so what a fold is hiding is never a mystery. */
 function descendantsOf(comment: Comment): number {
@@ -179,7 +195,9 @@ function renderComment(comment: Comment, depth: number): Raw {
           }</span>`
         : ''}
     </summary>
-    ${comment.text ? html`<div class="c__body">${renderMarkdown(comment.text)}</div>` : ''}
+    ${comment.text
+      ? html`<div class="c__body">${renderMarkdown(comment.text, renderCommentImage)}</div>`
+      : ''}
     ${comment.replies.length || comment.moreReplies
       ? html`<div class="c__replies">
           ${comment.replies.map((reply) => renderComment(reply, depth + 1))}

test/markdown.test.ts

@@ -1,9 +1,16 @@
 import assert from 'node:assert/strict';
 import { test } from 'node:test';
+import { escapeHtml } from '../src/render/html.ts';
 import { renderMarkdown } from '../src/render/markdown.ts';
 
 const md = (text: string): string => String(renderMarkdown(text));
 
+/** Stands in for the real one, which proxies. Escapes the way that one does:
+ *  placing the image is the renderer's job, and so is making it safe. */
+const img = (url: string, alt: string): string =>
+  `<img src="${escapeHtml(url)}" alt="${escapeHtml(alt)}">`;
+const mdi = (text: string): string => String(renderMarkdown(text, img));
+
 test('markup a commenter typed is text, not markup', () => {
   const out = md('<script>alert(1)</script> & "quoted"');
   assert.ok(!out.includes('<script>'));
@@ -64,3 +71,85 @@ test('a single newline inside a paragraph is a line break, a blank line is a new
   assert.equal(md('one\ntwo'), '<p>one<br>two</p>');
   assert.equal(md('one\n\ntwo'), '<p>one</p><p>two</p>');
 });
+
+test('an image is a picture when there is something to place it with', () => {
+  assert.equal(mdi('![a cat](https://i.redd.it/x.jpg)'),
+    '<p><img src="https://i.redd.it/x.jpg" alt="a cat"></p>');
+});
+
+test('an image degrades to a link when there is not', () => {
+  const out = md('![a cat](https://i.redd.it/x.jpg)');
+  assert.ok(out.includes('<a href="https://i.redd.it/x.jpg"'));
+  assert.ok(!out.includes('<img'));
+});
+
+test("an image's `!` is not left behind as text", () => {
+  // The link rule would otherwise match from the `[` and strand the bang.
+  assert.ok(!mdi('![](https://i.redd.it/x.png)').includes('!'));
+});
+
+test('a pasted image address becomes the picture, not a link to it', () => {
+  // Which is how most images in a Reddit comment arrive.
+  const out = mdi('look\n\nhttps://preview.redd.it/abc.jpeg?width=1274&s=deadbeef');
+  assert.ok(out.includes('<img src="https://preview.redd.it/abc.jpeg?width=1274&amp;s=deadbeef"'));
+  assert.ok(!out.includes('<a href'));
+});
+
+test('a link that is not an image is still a link', () => {
+  const out = mdi('see https://example.com/article');
+  assert.ok(out.includes('<a href="https://example.com/article"'));
+  assert.ok(!out.includes('<img'));
+});
+
+test('a sentence after a pasted image keeps its punctuation out of the address', () => {
+  const out = mdi('here https://i.redd.it/x.jpg.');
+  assert.ok(out.includes('src="https://i.redd.it/x.jpg"'), out);
+  assert.ok(out.endsWith('.</p>'), out);
+});
+
+test('only http and https become pictures', () => {
+  const out = mdi('![x](javascript:alert(1))');
+  assert.ok(!out.includes('<img'));
+  assert.ok(out.includes('![x]'));
+});
+
+test("an image's alt text is escaped like anything else a stranger wrote", () => {
+  const out = mdi('![" onerror=alert(1)](https://i.redd.it/x.jpg)');
+  assert.ok(!out.includes('onerror=alert(1)>'), out);
+  assert.ok(out.includes('&quot;'));
+});
+
+test('images inside a quote are still placed', () => {
+  assert.match(mdi('> ![](https://i.redd.it/x.gif)'), /<blockquote><p><img/);
+});
+
+test('an image address typed without a scheme is still the picture', () => {
+  // Which is how people type them: no https, straight from the address bar.
+  const out = mdi('preview.redd.it/lz4drsqh0clh1.jpeg?width=1290&s=b27e');
+  assert.ok(out.includes('<img src="https://preview.redd.it/lz4drsqh0clh1.jpeg?width=1290&amp;s=b27e"'), out);
+});
+
+test('a schemeless image address mid-sentence keeps the sentence', () => {
+  const out = mdi('look at i.redd.it/x.png nice one');
+  assert.ok(out.startsWith('<p>look at <img'), out);
+  assert.ok(out.endsWith(' nice one</p>'), out);
+});
+
+test('prose full of dots and slashes is not mistaken for an address', () => {
+  // The reason this rule insists on a host, a path and an image extension.
+  for (const text of [
+    'the file is at src/render/post.ts',
+    'see node_modules/foo/bar.js',
+    'a path like ./images/cat.jpg',
+    'C:/Users/x/cat.png',
+    'email [email protected]/nope.jpg',
+    'version 1.2.3/4.png',
+  ]) {
+    assert.ok(!mdi(text).includes('<img'), `treated as an image: ${text}`);
+  }
+});
+
+test('a schemeless address that is not an image is left alone', () => {
+  // Guessing a scheme is worth it for a picture and not for prose.
+  assert.equal(mdi('example.com/article'), '<p>example.com/article</p>');
+});

test/reddit.test.ts

@@ -1,6 +1,6 @@
 import assert from 'node:assert/strict';
 import { test } from 'node:test';
-import { commentsFrom, mediaFromLink, toPost, treeFromDepths } from '../src/platforms/reddit.ts';
+import { commentsFrom, mediaFromLink, resolveInlineImages, toPost, treeFromDepths } from '../src/platforms/reddit.ts';
 import { reddit } from '../src/platforms/reddit.ts';
 import { originalUrlFor } from '../src/platforms/index.ts';
 import { fixture } from './helpers.ts';
@@ -168,3 +168,82 @@ test('the page fallback rebuilds nesting from the depth on each comment', () =>
 test('a comment the page gave no text for is dropped rather than shown empty', () => {
   assert.deepEqual(treeFromDepths([{ depth: 0, author: 'a', score: 1, created: '', text: '' }]), []);
 });
+
+// Real shapes, captured from comments carrying each kind.
+const GIPHY = {
+  'giphy|Ve7wX45gaOFmw8eeEM': {
+    status: 'valid',
+    e: 'AnimatedImage',
+    m: 'image/gif',
+    s: {
+      y: 200,
+      x: 304,
+      gif: 'https://external-preview.redd.it/CTp8.gif?width=304&height=200&s=b0e9',
+      mp4: 'https://external-preview.redd.it/CTp8.gif?width=304&height=200&format=mp4&s=a389',
+    },
+  },
+};
+
+const UPLOAD = {
+  jo8gf0ca92zd1: {
+    status: 'valid',
+    e: 'Image',
+    m: 'image/jpeg',
+    s: { y: 1270, x: 1274, u: 'https://preview.redd.it/jo8gf0ca92zd1.jpeg?width=1274&s=c226' },
+  },
+};
+
+test('a giphy comment points at the gif rather than at a token', () => {
+  // `![gif](giphy|ID)` is not an address, and renders as nothing at all until
+  // it is looked up in the comment's own media_metadata.
+  assert.equal(
+    resolveInlineImages('![gif](giphy|Ve7wX45gaOFmw8eeEM)', GIPHY),
+    '![gif](https://external-preview.redd.it/CTp8.gif?width=304&height=200&s=b0e9)',
+  );
+});
+
+test('the animated form takes the gif, which plays on its own', () => {
+  const out = resolveInlineImages('![gif](giphy|Ve7wX45gaOFmw8eeEM)', GIPHY);
+  assert.ok(out.includes('.gif?'), out);
+  assert.ok(!out.includes('format=mp4'), 'an mp4 would need a player to move');
+});
+
+test('an uploaded image resolves through the same lookup', () => {
+  // Giphy, emotes and uploads are all a token that is a key in the same map,
+  // so none of them needs naming.
+  assert.equal(
+    resolveInlineImages('![img](jo8gf0ca92zd1)', UPLOAD),
+    '![img](https://preview.redd.it/jo8gf0ca92zd1.jpeg?width=1274&s=c226)',
+  );
+});
+
+test('a target that is already an address is left alone', () => {
+  const already = '![a](https://i.redd.it/x.jpg)';
+  assert.equal(resolveInlineImages(already, UPLOAD), already);
+  assert.equal(resolveInlineImages(already, undefined), already);
+});
+
+test('a token with no entry, or a broken one, is not invented', () => {
+  assert.equal(resolveInlineImages('![gif](giphy|missing)', GIPHY), '![gif](giphy|missing)');
+  assert.equal(
+    resolveInlineImages('![img](gone)', { gone: { status: 'failed', e: 'Image' } }),
+    '![img](gone)',
+  );
+});
+
+test('inline images survive the walk into the comment tree', () => {
+  const { comments } = commentsFrom({
+    data: {
+      children: [{
+        kind: 't1',
+        data: {
+          author: 'a',
+          body: 'ha ![gif](giphy|Ve7wX45gaOFmw8eeEM)',
+          media_metadata: GIPHY,
+          replies: '',
+        },
+      }],
+    },
+  });
+  assert.match(comments[0]?.text ?? '', /external-preview\.redd\.it/);
+});

test/render.test.ts

@@ -237,3 +237,21 @@ test('markup in a quoted post is escaped like any other stranger\'s text', () =>
   assert.ok(!html_.includes('<script>alert(1)</script>'));
   assert.ok(!html_.includes('<img src=x'));
 });
+
+test('a picture in a comment is proxied, and its alt text cannot break out', () => {
+  const page = renderPost(redditPost({
+    comments: [{
+      author: 'u/a',
+      text: '![" onerror=alert(1) x="](https://preview.redd.it/x.jpeg?s=abc)\n\nhttps://i.redd.it/y.png',
+      replies: [],
+    }],
+  }));
+
+  assert.ok(!page.includes('https://preview.redd.it/x.jpeg'), 'upstream URLs must not reach the page');
+  assert.ok(!page.includes('https://i.redd.it/y.png'), 'a pasted address is proxied too');
+  assert.equal((page.match(/<img class="c__img" src="\/m\//g) ?? []).length, 2);
+  // The payload survives as text inside the attribute, which is the point:
+  // its quotes are neutered, so it cannot close `alt="` and become markup.
+  assert.ok(page.includes('alt="&quot; onerror=alert(1) x=&quot;"'), 'alt text must be escaped');
+  assert.ok(!/alt="" onerror/.test(page), 'the attribute must not be closable');
+});