feat: collapse quoted reply text behind a "..." toggle #480

components/email/email-viewer.tsx

@@ -7,6 +7,7 @@ import { emailExportFilename, attachmentDownloadFilename, attachmentsBundleFilen
 import { EML_IMPORT_ACCEPT, expandImportableEmails } from "@/lib/eml-import";
 import { EMAIL_IFRAME_SANITIZE_CONFIG, applyNewTabToAnchor, blockExternalResourcesOnNode, collapseBlockedImageContainers, escapeHtml, plainTextToSafeHtml, sanitizeEmailHtml, sanitizePlainTextRenderedHtml } from "@/lib/email-sanitization";
 import { hasMeaningfulHtmlBody } from "@/lib/signature-utils";
+import { collapsePlainTextQuotes, setupQuoteCollapse } from "@/lib/quote-collapse";
 import { withBasePath } from "@/lib/browser-navigation";
 import { Button } from "@/components/ui/button";
 import { Avatar } from "@/components/ui/avatar";
@@ -1702,7 +1703,11 @@ export function EmailViewer({
         const textContent = email.bodyValues[email.textBody[0].partId].value;
 
         return {
-          html: plainTextToSafeHtml(textContent),
+          // Trailing ">"-quoted block collapses behind a <details> toggle (#480).
+          html: collapsePlainTextQuotes(plainTextToSafeHtml(textContent), {
+            show: t('show_quoted_text'),
+            hide: t('hide_quoted_text'),
+          }),
           isHtml: false,
           hasStyleTag: false,
           externalBlocked: false,
@@ -1742,6 +1747,11 @@ export function EmailViewer({
 
   // Override email content with S/MIME decrypted content when available
   const effectiveEmailContent = useMemo(() => {
+    const plainToHtml = (text: string) =>
+      collapsePlainTextQuotes(plainTextToSafeHtml(text), {
+        show: t('show_quoted_text'),
+        hide: t('hide_quoted_text'),
+      });
     if (pluginRenderedHtml) {
       const htmlWithCidUrls = pluginRenderedHtml.replace(
         /\bcid:([^"'\s)]+)/gi,
@@ -1753,7 +1763,7 @@ export function EmailViewer({
       return { html: cleanHtml, isHtml: true, hasStyleTag: /<style[\s>]/i.test(pluginRenderedHtml), externalBlocked: false };
     }
     if (pluginRenderedText) {
-      return { html: plainTextToSafeHtml(pluginRenderedText), isHtml: false, hasStyleTag: false, externalBlocked: false };
+      return { html: plainToHtml(pluginRenderedText), isHtml: false, hasStyleTag: false, externalBlocked: false };
     }
     // TNEF (winmail.dat) extracted content
     if (tnefHtml) {
@@ -1761,7 +1771,7 @@ export function EmailViewer({
       return { html: cleanHtml, isHtml: true, hasStyleTag: /<style[\s>]/i.test(tnefHtml), externalBlocked: false };
     }
     if (tnefText) {
-      return { html: plainTextToSafeHtml(tnefText), isHtml: false, hasStyleTag: false, externalBlocked: false };
+      return { html: plainToHtml(tnefText), isHtml: false, hasStyleTag: false, externalBlocked: false };
     }
     // Embedded message/rfc822 unwrapped content
     if (embeddedEmailHtml) {
@@ -1769,10 +1779,10 @@ export function EmailViewer({
       return { html: cleanHtml, isHtml: true, hasStyleTag: /<style[\s>]/i.test(embeddedEmailHtml), externalBlocked: false };
     }
     if (embeddedEmailText) {
-      return { html: plainTextToSafeHtml(embeddedEmailText), isHtml: false, hasStyleTag: false, externalBlocked: false };
+      return { html: plainToHtml(embeddedEmailText), isHtml: false, hasStyleTag: false, externalBlocked: false };
     }
     return emailContent;
-  }, [cidBlobUrls, emailContent, pluginRenderedHtml, pluginRenderedText, tnefHtml, tnefText, embeddedEmailHtml, embeddedEmailText]);
+  }, [cidBlobUrls, emailContent, pluginRenderedHtml, pluginRenderedText, tnefHtml, tnefText, embeddedEmailHtml, embeddedEmailText, t]);
 
   const resolveAttachmentName = useCallback(
     (attachment: EffectiveAttachment) => {
@@ -2244,6 +2254,14 @@ export function EmailViewer({
       if (initializedDocRef.current === doc) return;
       initializedDocRef.current = doc;
       {
+        // Collapse the quoted original of a reply behind a "•••" toggle
+        // (#480). Before the height wiring, so the initial measurement
+        // already reflects the collapsed body.
+        setupQuoteCollapse(doc, {
+          show: t('show_quoted_text'),
+          hide: t('hide_quoted_text'),
+        });
+
         // Auto-resize iframe to fit content
         // Measure max(documentElement, body): a height:100% wrapper can leave
         // documentElement.scrollHeight short while the real content lives in body.
@@ -2415,7 +2433,7 @@ export function EmailViewer({
     } catch {
       // Cross-origin restrictions - iframe will still display content
     }
-  }, [isDark, emailHasNativeDarkMode, email?.id]);
+  }, [isDark, emailHasNativeDarkMode, email?.id, t]);
 
   // Wire up the iframe as soon as its sandboxed document has parsed, rather than
   // waiting for the iframe 'load' event. 'load' also waits on every subresource,

components/email/thread-conversation-view.tsx

@@ -5,6 +5,7 @@ import DOMPurify from "dompurify";
 import { Email, ThreadGroup } from "@/lib/jmap/types";
 import { EMAIL_SANITIZE_CONFIG, collapseBlockedImageContainers, plainTextToSafeHtml, sanitizePlainTextRenderedHtml } from "@/lib/email-sanitization";
 import { hasMeaningfulHtmlBody } from "@/lib/signature-utils";
+import { collapsePlainTextQuotes, setupQuoteCollapse } from "@/lib/quote-collapse";
 import { transformInlineStyles, transformColorForDarkMode, transformBgColorForDarkMode } from "@/lib/color-transform";
 import { useThemeStore } from "@/stores/theme-store";
 import { Avatar } from "@/components/ui/avatar";
@@ -424,7 +425,14 @@ function EmailCard({
       // Plain text fallback
       if (email.textBody?.[0]?.partId && email.bodyValues[email.textBody[0].partId]) {
         const text = email.bodyValues[email.textBody[0].partId].value;
-        return { html: plainTextToSafeHtml(text, 'text-primary hover:underline'), isHtml: false };
+        return {
+          // Trailing ">"-quoted block collapses behind a <details> toggle (#480).
+          html: collapsePlainTextQuotes(plainTextToSafeHtml(text, 'text-primary hover:underline'), {
+            show: t('email_viewer.show_quoted_text'),
+            hide: t('email_viewer.hide_quoted_text'),
+          }),
+          isHtml: false,
+        };
       }
     }
 
@@ -438,7 +446,7 @@ function EmailCard({
     }
 
     return { html: "", isHtml: false };
-  }, [email, allowExternal, resolvedTheme, emailAlwaysLightMode, cidBlobUrls]);
+  }, [email, allowExternal, resolvedTheme, emailAlwaysLightMode, cidBlobUrls, t]);
 
   // Render the sanitized HTML body inside a sandboxed iframe so a malicious
   // (or accidentally-bypassed) email cannot inject styles/scripts/forms into
@@ -469,6 +477,12 @@ function EmailCard({
     try {
       const doc = iframe.contentDocument;
       if (!doc?.body) return;
+      // Collapse the quoted original of a reply behind a "•••" toggle (#480),
+      // before the first resize so the height reflects the collapsed body.
+      setupQuoteCollapse(doc, {
+        show: t('email_viewer.show_quoted_text'),
+        hide: t('email_viewer.hide_quoted_text'),
+      });
       const resize = () => {
         iframe.style.height = doc.documentElement.scrollHeight + 'px';
       };
@@ -482,7 +496,7 @@ function EmailCard({
     } catch {
       // contentDocument may be inaccessible under stricter sandboxes; ignore.
     }
-  }, []);
+  }, [t]);
 
   return (
     <div className={cn(

lib/__tests__/quote-collapse.test.ts

@@ -0,0 +1,248 @@
+import { describe, it, expect, beforeEach } from 'vitest';
+
+import { setupQuoteCollapse, collapsePlainTextQuotes, QUOTE_TOGGLE_ATTR, QUOTE_COLLAPSED_ATTR } from '@/lib/quote-collapse';
+import { plainTextToSafeHtml, sanitizeEmailHtml, sanitizePlainTextRenderedHtml } from '@/lib/email-sanitization';
+
+const labels = { show: 'Show quoted text', hide: 'Hide quoted text' };
+
+const toggle = () => document.body.querySelector<HTMLButtonElement>(`[${QUOTE_TOGGLE_ATTR}]`);
+
+describe('setupQuoteCollapse', () => {
+  beforeEach(() => {
+    document.body.innerHTML = '';
+  });
+
+  it('collapses a Gmail-style trailing quote behind a toggle', () => {
+    document.body.innerHTML = `
+      <div dir="ltr">Thanks, sounds good!</div>
+      <div class="gmail_quote">
+        <div class="gmail_attr">On Mon, Jul 20, 2026 John wrote:</div>
+        <blockquote>Original message body</blockquote>
+      </div>`;
+    expect(setupQuoteCollapse(document, labels)).toBe(true);
+
+    const quote = document.querySelector<HTMLElement>('.gmail_quote')!;
+    expect(quote.style.display).toBe('none');
+    const btn = toggle()!;
+    expect(btn).toBeTruthy();
+    expect(btn.getAttribute('aria-expanded')).toBe('false');
+    expect(btn.title).toBe(labels.show);
+    // Button sits directly before the quote it controls.
+    expect(btn.nextElementSibling).toBe(quote);
+  });
+
+  it('toggle expands and re-collapses, restoring the original inline display', () => {
+    document.body.innerHTML = `
+      <p>reply text</p>
+      <div class="gmail_quote" style="display:flex">quoted</div>`;
+    setupQuoteCollapse(document, labels);
+
+    const quote = document.querySelector<HTMLElement>('.gmail_quote')!;
+    const btn = toggle()!;
+    btn.click();
+    expect(quote.style.display).toBe('flex');
+    expect(quote.hasAttribute(QUOTE_COLLAPSED_ATTR)).toBe(false);
+    expect(btn.getAttribute('aria-expanded')).toBe('true');
+    expect(btn.title).toBe(labels.hide);
+
+    btn.click();
+    expect(quote.style.display).toBe('none');
+    expect(btn.getAttribute('aria-expanded')).toBe('false');
+    expect(btn.title).toBe(labels.show);
+  });
+
+  it('collapses an Apple Mail cite blockquote but keeps the attribution line visible', () => {
+    document.body.innerHTML = `
+      <div>See you then.</div>
+      <div>On 20 Jul 2026, at 10:00, Jane wrote:</div>
+      <blockquote type="cite">the original</blockquote>`;
+    expect(setupQuoteCollapse(document, labels)).toBe(true);
+
+    const quote = document.querySelector<HTMLElement>('blockquote')!;
+    expect(quote.style.display).toBe('none');
+    expect(document.body.textContent).toContain('Jane wrote:');
+  });
+
+  it('collapses Bulwark\'s own data-quoted-html reply island', () => {
+    document.body.innerHTML = `
+      <p>my answer</p>
+      <div>On Jul 20, John &lt;j@example.com&gt; wrote:</div>
+      <div data-quoted-html style="border-left:2px solid #c5c5c5;padding-left:12px;">original</div>`;
+    expect(setupQuoteCollapse(document, labels)).toBe(true);
+    expect(document.querySelector<HTMLElement>('[data-quoted-html]')!.style.display).toBe('none');
+  });
+
+  it('collapses everything after an Outlook divRplyFwdMsg separator', () => {
+    document.body.innerHTML = `
+      <div>Top-posted answer</div>
+      <div id="divRplyFwdMsg"><b>From:</b> John<br><b>Sent:</b> Monday</div>
+      <div>quoted paragraph one</div>
+      <div>quoted paragraph two</div>`;
+    expect(setupQuoteCollapse(document, labels)).toBe(true);
+
+    const divs = [...document.querySelectorAll<HTMLElement>('body > div')];
+    expect(divs[0].style.display).toBe('');
+    expect(divs[1].style.display).toBe('none');
+    expect(divs[2].style.display).toBe('none');
+    expect(divs[3].style.display).toBe('none');
+  });
+
+  it('collapses from a Thunderbird moz-cite-prefix attribution onwards', () => {
+    document.body.innerHTML = `
+      <p>reply</p>
+      <div class="moz-cite-prefix">On 20.07.2026, Jane wrote:</div>
+      <blockquote type="cite">original</blockquote>`;
+    expect(setupQuoteCollapse(document, labels)).toBe(true);
+    expect(document.querySelector<HTMLElement>('.moz-cite-prefix')!.style.display).toBe('none');
+    expect(document.querySelector<HTMLElement>('blockquote')!.style.display).toBe('none');
+  });
+
+  it('does not collapse when the quote is the entire message', () => {
+    document.body.innerHTML = `
+      <div class="gmail_quote">forwarded content only</div>`;
+    expect(setupQuoteCollapse(document, labels)).toBe(false);
+    expect(toggle()).toBeNull();
+    expect(document.querySelector<HTMLElement>('.gmail_quote')!.style.display).toBe('');
+  });
+
+  it('does not collapse an interleaved reply (content after the quote container)', () => {
+    document.body.innerHTML = `
+      <p>first point</p>
+      <blockquote type="cite">their question</blockquote>
+      <p>my answer below the quote</p>`;
+    expect(setupQuoteCollapse(document, labels)).toBe(false);
+    expect(toggle()).toBeNull();
+  });
+
+  it('ignores whitespace-only trailing content after the quote container', () => {
+    document.body.innerHTML = `
+      <p>reply</p>
+      <div class="gmail_quote">quoted</div>
+      <div><br></div>
+      ${String.fromCharCode(160)}`;
+    expect(setupQuoteCollapse(document, labels)).toBe(true);
+  });
+
+  it('is idempotent per document', () => {
+    document.body.innerHTML = `
+      <p>reply</p>
+      <div class="gmail_quote">quoted</div>`;
+    expect(setupQuoteCollapse(document, labels)).toBe(true);
+    expect(setupQuoteCollapse(document, labels)).toBe(false);
+    expect(document.querySelectorAll(`[${QUOTE_TOGGLE_ATTR}]`)).toHaveLength(1);
+  });
+
+  it('does nothing when no quote marker exists', () => {
+    document.body.innerHTML = `<p>plain email with content</p><p>and more content</p>`;
+    expect(setupQuoteCollapse(document, labels)).toBe(false);
+    expect(toggle()).toBeNull();
+  });
+
+  it('collapses a bare blockquote preceded by an attribution line ending in a colon', () => {
+    // Shape of a Bulwark reply to a plain-text original (issue #480 follow-up):
+    // no type/class on the blockquote, attribution in the preceding <p>.
+    document.body.innerHTML = `
+      <div>
+        <p>Hi Tracey,<br>thanks for reaching out.</p>
+        <p>On Mo., 18. Mai 2026, 20:27, Tracey Tiefisher wrote:<br></p>
+        <blockquote><p>Hi Linus,</p><blockquote><p>older nested quote</p></blockquote></blockquote>
+        <p></p>
+      </div>`;
+    expect(setupQuoteCollapse(document, labels)).toBe(true);
+    const outer = document.querySelector<HTMLElement>('blockquote')!;
+    expect(outer.style.display).toBe('none');
+    expect(document.body.textContent).toContain('Tracey Tiefisher wrote:');
+  });
+
+  it('leaves a bare blockquote alone when the preceding text is not an attribution', () => {
+    document.body.innerHTML = `
+      <p>Our newsletter quote of the day</p>
+      <blockquote>Stay hungry, stay foolish.</blockquote>`;
+    expect(setupQuoteCollapse(document, labels)).toBe(false);
+    expect(toggle()).toBeNull();
+  });
+
+  it('collapses a nested wrapper case: separator inside a wrapper div hides content outside it too', () => {
+    document.body.innerHTML = `
+      <div>answer</div>
+      <div><div id="appendonsend"></div><div>quoted intro</div></div>
+      <div>quoted rest</div>`;
+    expect(setupQuoteCollapse(document, labels)).toBe(true);
+    const last = document.body.lastElementChild as HTMLElement;
+    expect(last.textContent).toBe('quoted rest');
+    expect(last.style.display).toBe('none');
+  });
+});
+
+describe('sanitizer keeps the quote marker attribute', () => {
+  it('preserves data-quoted-html through sanitizeEmailHtml', () => {
+    const out = sanitizeEmailHtml('<p>hi</p><div data-quoted-html style="padding-left:12px">orig</div>');
+    expect(out).toContain('data-quoted-html');
+  });
+});
+
+describe('collapsePlainTextQuotes', () => {
+  const raw = [
+    'Hallo Linus,',
+    '',
+    'ich sehe eben, dass du das gefixt hast, thx!',
+    '',
+    'On Dienstag, 31. Maerz 2026 13:56 Richard Weinberger wrote:',
+    '> On Dienstag, 31. Maerz 2026 00:28 Richard Weinberger wrote:',
+    '> > Hi!',
+    '> ',
+    '> Here are some more issues:',
+    '> ',
+    '> - getClientIP() vulnerable to IP spoofing.',
+    '',
+    '',
+    '-- ',
+    'sigma star gmbh | Eduard-Bodem-Gasse 6, 6020 Innsbruck, AUT',
+  ].join('\n');
+
+  it('wraps the trailing quote run in <details>, keeping reply, attribution and signature visible', () => {
+    const out = collapsePlainTextQuotes(plainTextToSafeHtml(raw), labels);
+    expect(out).toContain('<details>');
+    expect(out).toContain('•••');
+    expect(out).toContain(`title="${labels.show}"`);
+    // Quote run is inside the details, attribution and signature outside.
+    const details = out.slice(out.indexOf('<details>'), out.indexOf('</details>'));
+    expect(details).toContain('getClientIP()');
+    // The nested quoted attribution (00:28) collapses, the outer one (13:56) stays.
+    expect(details).toContain('00:28');
+    expect(details).not.toContain('13:56');
+    const outside = out.replace(details, '');
+    expect(outside).toContain('Hallo Linus,');
+    expect(outside).toContain('13:56 Richard Weinberger wrote:');
+    expect(outside).toContain('sigma star gmbh');
+  });
+
+  it('round-trips through sanitizePlainTextRenderedHtml', () => {
+    const out = sanitizePlainTextRenderedHtml(collapsePlainTextQuotes(plainTextToSafeHtml(raw), labels));
+    expect(out).toContain('<details>');
+    expect(out).toContain('<summary');
+    expect(out).toContain(`title="${labels.show}"`);
+  });
+
+  it('does not collapse a bottom-posted reply (content after the quote run)', () => {
+    const text = 'Tom wrote:\n> what do you think?\n\nSounds good to me!';
+    const safe = plainTextToSafeHtml(text);
+    expect(collapsePlainTextQuotes(safe, labels)).toBe(safe);
+  });
+
+  it('does not collapse when the quote is the whole message', () => {
+    const text = '> forwarded line one\n> forwarded line two';
+    const safe = plainTextToSafeHtml(text);
+    expect(collapsePlainTextQuotes(safe, labels)).toBe(safe);
+  });
+
+  it('leaves mail without quote lines untouched', () => {
+    const safe = plainTextToSafeHtml('just a normal message\nwith two lines');
+    expect(collapsePlainTextQuotes(safe, labels)).toBe(safe);
+  });
+
+  it('never treats a ">" mid-line as a quote', () => {
+    const safe = plainTextToSafeHtml('a -> b\nx > y comparison');
+    expect(collapsePlainTextQuotes(safe, labels)).toBe(safe);
+  });
+});

lib/email-sanitization.ts

@@ -8,7 +8,11 @@ import DOMPurify from 'dompurify';
  */
 export const EMAIL_SANITIZE_CONFIG = {
   ADD_TAGS: [],
-  ADD_ATTR: ['target', 'rel', 'style', 'class', 'width', 'height', 'align', 'valign', 'bgcolor', 'color'],
+  // data-quoted-html is Bulwark's own reply-quote marker (see
+  // components/email/quoted-html.ts). Explicitly whitelisted despite
+  // ALLOW_DATA_ATTR:false so the viewer can detect and collapse the quoted
+  // original (lib/quote-collapse.ts); it's inert otherwise.
+  ADD_ATTR: ['target', 'rel', 'style', 'class', 'width', 'height', 'align', 'valign', 'bgcolor', 'color', 'data-quoted-html'],
   ALLOW_DATA_ATTR: false,
   FORCE_BODY: true,
   // Allow blob: URIs so authenticated inline images (CID) are not stripped.
@@ -182,8 +186,10 @@ export function sanitizeI18nHtml(html: string): string {
  * future code path passes raw HTML in by mistake.
  */
 const PLAIN_TEXT_RENDERED_CONFIG = {
-  ALLOWED_TAGS: ['a', 'br', 'p', 'div', 'span'],
+  // details/summary/title carry the script-less quote-collapse toggle emitted
-  ALLOWED_ATTR: ['href', 'target', 'rel', 'class', 'style'],
+  // by collapsePlainTextQuotes (lib/quote-collapse.ts).
+  ALLOWED_TAGS: ['a', 'br', 'p', 'div', 'span', 'details', 'summary'],
+  ALLOWED_ATTR: ['href', 'target', 'rel', 'class', 'style', 'title'],
   // DOMPurify URI-tests every attribute value not on its URI-safe list, so the
   // strict ALLOWED_URI_REGEXP below would strip target="_blank" (and rel) —
   // "_blank" is not a URI. This branch renders into the main document rather

lib/quote-collapse.ts

@@ -0,0 +1,259 @@
+/**
+ * Quote collapsing for the email viewer (issue #480).
+ *
+ * When a reply carries the original message as a trailing quote, hide it by
+ * default and inject a Gmail-style "•••" pill that toggles it. Runs against
+ * the live iframe DOM from the parent frame AFTER sanitization, so the
+ * injected button and its click listener are not subject to the sanitizer or
+ * the iframe's script-blocking CSP (parent-attached DOM listeners still fire).
+ *
+ * Two kinds of markers:
+ *  - container: an element that wraps the entire quoted original. Hiding the
+ *    element hides the quote.
+ *  - separator: a header/divider element ("From: …" block, attribution line)
+ *    that the quoted original FOLLOWS as siblings. Everything from the marker
+ *    to the end of the body is hidden.
+ */
+
+// Order matters only for readability - document order decides which marker
+// wins when several are present (querySelector on the comma-joined list).
+const CONTAINER_SELECTORS = [
+  // Bulwark's own reply/forward island (see components/email/quoted-html.ts).
+  // The attribute survives sanitization via an explicit ADD_ATTR entry.
+  'div[data-quoted-html]',
+  // Gmail: gmail_quote_container (2023+) wraps gmail_attr + gmail_quote.
+  'div.gmail_quote_container',
+  'div.gmail_quote',
+  // Apple Mail / Thunderbird quoted body.
+  'blockquote[type="cite"]',
+  'div.yahoo_quoted',
+  'blockquote.protonmail_quote',
+  'div.protonmail_quote',
+];
+
+const SEPARATOR_SELECTORS = [
+  // Outlook (desktop + OWA): "From:/Sent:/To:/Subject:" header block; the
+  // quoted message body follows as siblings.
+  '#divRplyFwdMsg',
+  '#appendonsend',
+  // Thunderbird attribution line ("On …, X wrote:"); the blockquote follows.
+  'div.moz-cite-prefix',
+];
+
+const ALL_SELECTORS = [...CONTAINER_SELECTORS, ...SEPARATOR_SELECTORS].join(',');
+
+/** Marks the injected toggle button (also the idempotence guard). */
+export const QUOTE_TOGGLE_ATTR = 'data-quote-toggle';
+/** Marks elements hidden by the collapse; value stores the original inline display. */
+export const QUOTE_COLLAPSED_ATTR = 'data-quote-collapsed';
+
+export interface QuoteCollapseLabels {
+  /** Accessible label/tooltip while collapsed, e.g. "Show quoted text". */
+  show: string;
+  /** Accessible label/tooltip while expanded, e.g. "Hide quoted text". */
+  hide: string;
+}
+
+/** True when any text node outside `marker` on the given side of it has visible content. */
+function hasVisibleContent(body: HTMLElement, marker: Element, side: 'before' | 'after'): boolean {
+  const positionBit = side === 'before'
+    ? Node.DOCUMENT_POSITION_PRECEDING
+    : Node.DOCUMENT_POSITION_FOLLOWING;
+  const doc = body.ownerDocument;
+  const walker = doc.createTreeWalker(body, NodeFilter.SHOW_TEXT | NodeFilter.SHOW_ELEMENT);
+  for (let node = walker.nextNode(); node; node = walker.nextNode()) {
+    const rel = marker.compareDocumentPosition(node);
+    // Skip the marker's own subtree and anything not on the requested side.
+    if (rel & Node.DOCUMENT_POSITION_CONTAINED_BY) continue;
+    if (!(rel & positionBit)) continue;
+    if (node.nodeType === Node.TEXT_NODE) {
+      if ((node.nodeValue || '').trim() !== '') return true;
+    } else if ((node as Element).tagName === 'IMG') {
+      // An image counts as content (image-only replies exist), but not the
+      // 1x1 placeholders left by blocked external images.
+      const img = node as HTMLImageElement;
+      if (!img.hasAttribute('data-blocked-src') && (img.style.display !== 'none')) return true;
+    }
+  }
+  return false;
+}
+
+/**
+ * Fallback for replies whose quote is a bare <blockquote> (no type/class -
+ * e.g. Bulwark's own reply to a plain-text original, and various mobile
+ * clients): an outermost blockquote directly preceded by an attribution line.
+ * Attribution is sniffed language-agnostically as the nearest preceding text
+ * ending with a colon ("On …, X wrote:", "Am … schrieb X:", "… a écrit :").
+ */
+function findAttributedBlockquote(body: HTMLElement): Element | null {
+  for (const bq of Array.from(body.querySelectorAll('blockquote'))) {
+    if (bq.parentElement?.closest('blockquote')) continue; // outermost only
+    if (precedingTextEndsWithColon(body, bq)) return bq;
+  }
+  return null;
+}
+
+/** True when the last non-blank text node before `el` ends with a colon. */
+function precedingTextEndsWithColon(body: HTMLElement, el: Element): boolean {
+  const walker = body.ownerDocument.createTreeWalker(body, NodeFilter.SHOW_TEXT);
+  let last: string | null = null;
+  for (let node = walker.nextNode(); node; node = walker.nextNode()) {
+    const rel = el.compareDocumentPosition(node);
+    if (rel & Node.DOCUMENT_POSITION_CONTAINED_BY) continue;
+    if (!(rel & Node.DOCUMENT_POSITION_PRECEDING)) break; // reached/passed el
+    const text = (node.nodeValue || '').trim();
+    if (text !== '') last = text;
+  }
+  return last !== null && last.endsWith(':');
+}
+
+/** Hide an element, remembering its original inline display for restore. */
+function hideElement(el: HTMLElement): void {
+  el.setAttribute(QUOTE_COLLAPSED_ATTR, el.style.display || '');
+  el.style.display = 'none';
+}
+
+/**
+ * The elements to hide for a separator marker: the marker itself plus
+ * everything after it in document order (climbing to body handles markers
+ * nested inside wrapper divs).
+ */
+function collectSeparatorRange(body: HTMLElement, marker: Element): HTMLElement[] {
+  const range: HTMLElement[] = [marker as HTMLElement];
+  let el: Element | null = marker;
+  while (el && el !== body) {
+    for (let sib = el.nextElementSibling; sib; sib = sib.nextElementSibling) {
+      range.push(sib as HTMLElement);
+    }
+    el = el.parentElement;
+  }
+  return range;
+}
+
+/**
+ * Detect a trailing quoted original in `doc` and collapse it behind a "•••"
+ * toggle button. No-op (returns false) when no marker is found, when the
+ * quote IS the whole message (nothing visible before it - collapsing would
+ * render the mail as a lone button), or - for container markers - when
+ * visible content follows the quote (interleaved/bottom-posted reply, where
+ * hiding "the rest" would swallow real content).
+ *
+ * Idempotent per document. Returns true when a quote was collapsed.
+ */
+export function setupQuoteCollapse(doc: Document, labels: QuoteCollapseLabels): boolean {
+  const body = doc.body;
+  if (!body || body.querySelector(`[${QUOTE_TOGGLE_ATTR}]`)) return false;
+
+  const marker = body.querySelector(ALL_SELECTORS) ?? findAttributedBlockquote(body);
+  if (!marker) return false;
+
+  const isSeparator = SEPARATOR_SELECTORS.some((sel) => marker.matches(sel));
+
+  // Never collapse the entire message down to just the toggle.
+  if (!hasVisibleContent(body, marker, 'before')) return false;
+  // Interleaved reply: real content after the quote container - leave as is.
+  if (!isSeparator && hasVisibleContent(body, marker, 'after')) return false;
+
+  const hidden = isSeparator
+    ? collectSeparatorRange(body, marker)
+    : [marker as HTMLElement];
+
+  const button = doc.createElement('button');
+  button.type = 'button';
+  button.setAttribute(QUOTE_TOGGLE_ATTR, '');
+  button.setAttribute('aria-expanded', 'false');
+  button.setAttribute('aria-label', labels.show);
+  button.title = labels.show;
+  button.textContent = '•••';
+  // Inline styles only: the iframe has no app CSS, and style-src allows
+  // inline. Neutral grays read fine after the dark-mode invert filter too.
+  button.style.cssText =
+    'display:inline-block;margin:12px 0 4px;padding:3px 12px;border:none;' +
+    'border-radius:999px;background:#e3e6ea;color:#3c4043;font-size:11px;' +
+    'line-height:1;letter-spacing:2px;cursor:pointer;font-family:inherit;';
+  button.addEventListener('mouseenter', () => { button.style.background = '#d4d8dd'; });
+  button.addEventListener('mouseleave', () => { button.style.background = '#e3e6ea'; });
+
+  marker.parentNode?.insertBefore(button, marker);
+  hidden.forEach(hideElement);
+
+  button.addEventListener('click', () => {
+    const expanded = button.getAttribute('aria-expanded') === 'true';
+    hidden.forEach((el) => {
+      if (expanded) {
+        hideElement(el);
+      } else {
+        el.style.display = el.getAttribute(QUOTE_COLLAPSED_ATTR) || '';
+        el.removeAttribute(QUOTE_COLLAPSED_ATTR);
+      }
+    });
+    button.setAttribute('aria-expanded', String(!expanded));
+    const label = expanded ? labels.show : labels.hide;
+    button.setAttribute('aria-label', label);
+    button.title = label;
+  });
+
+  return true;
+}
+
+const escapeAttr = (s: string) =>
+  s.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/"/g, '&quot;');
+
+/**
+ * Collapse the trailing ">"-quoted block of a plain-text email.
+ *
+ * Operates on the ESCAPED html produced by plainTextToSafeHtml (lines are
+ * plain text with entities plus <a> tags, still newline-separated), because
+ * the plain-text branch renders into the main DOM via dangerouslySetInnerHTML
+ * - there is no post-render hook to attach a JS toggle to. Instead the quote
+ * run is wrapped in native <details>/<summary>, which toggles without any
+ * script and survives sanitizePlainTextRenderedHtml (details/summary are
+ * whitelisted there for exactly this markup).
+ *
+ * Collapsed: the last run of "&gt;"-prefixed lines (interior blank lines
+ * included). Left visible: everything before it (reply + attribution line),
+ * and a trailing "-- " signature block after it. No-op when real content
+ * follows the run (bottom-posted/interleaved reply), when there is no content
+ * before it, or when there are no quote lines at all.
+ */
+export function collapsePlainTextQuotes(safeHtml: string, labels: QuoteCollapseLabels): string {
+  const lines = safeHtml.split('\n');
+  const isQuote = (l: string) => /^\s*&gt;/.test(l);
+
+  let end = -1;
+  for (let i = lines.length - 1; i >= 0; i--) {
+    if (isQuote(lines[i])) { end = i; break; }
+  }
+  if (end === -1) return safeHtml;
+
+  // Everything after the run must be blank or a "-- " signature block.
+  let inSignature = false;
+  for (let i = end + 1; i < lines.length; i++) {
+    if (inSignature || lines[i].trim() === '') continue;
+    if (/^--\s*$/.test(lines[i].trim())) { inSignature = true; continue; }
+    return safeHtml;
+  }
+
+  // Walk back to the start of the run; blank lines BETWEEN quote lines are
+  // part of it (start only ever lands on a quote line).
+  let start = end;
+  for (let i = end - 1; i >= 0; i--) {
+    if (isQuote(lines[i])) start = i;
+    else if (lines[i].trim() !== '') break;
+  }
+
+  // Never collapse the entire message down to just the toggle.
+  if (!lines.slice(0, start).some((l) => l.trim() !== '')) return safeHtml;
+
+  const before = lines.slice(0, start).join('\n');
+  const quoted = lines.slice(start, end + 1).join('\n');
+  const after = lines.slice(end + 1).join('\n');
+  // Same pill look as the HTML-path toggle button; list-style:none hides the
+  // native disclosure triangle.
+  const summary =
+    `<summary title="${escapeAttr(labels.show)}" style="display:inline-block;` +
+    'list-style:none;margin:4px 0;padding:3px 12px;border-radius:999px;' +
+    'background:#e3e6ea;color:#3c4043;font-size:11px;line-height:1;' +
+    `letter-spacing:2px;cursor:pointer;">•••</summary>`;
+  return `${before}\n<details>${summary}${quoted}</details>${after ? '\n' + after : ''}`;
+}

locales/ar/common.json

@@ -277,6 +277,8 @@
     "no_subject": "(بلا موضوع)",
     "no_body_content": "(لا يوجد محتوى نصي متاح)",
     "no_preview_available": "لا تتوفر معاينة",
+    "show_quoted_text": "إظهار النص المقتبس",
+    "hide_quoted_text": "إخفاء النص المقتبس",
     "loading_email": "جارٍ تحميل الرسالة...",
     "loading": "جارٍ التحميل...",
     "reply": "رد",

locales/cs/common.json

@@ -277,6 +277,8 @@
     "no_subject": "(Bez předmětu)",
     "no_body_content": "(Žádný obsah těla)",
     "no_preview_available": "Náhled není k dispozici",
+    "show_quoted_text": "Zobrazit citovaný text",
+    "hide_quoted_text": "Skrýt citovaný text",
     "loading_email": "Načítání zprávy...",
     "loading": "Načítání...",
     "reply": "Odpovědět",

locales/da/common.json

@@ -277,6 +277,8 @@
     "no_subject": "(Intet emne)",
     "no_body_content": "(Intet indhold tilgængeligt)",
     "no_preview_available": "Forhåndsvisning ikke tilgængelig",
+    "show_quoted_text": "Vis citeret tekst",
+    "hide_quoted_text": "Skjul citeret tekst",
     "loading_email": "Indlæser e-mail...",
     "loading": "Indlæser...",
     "reply": "Svar",

locales/de/common.json

@@ -277,6 +277,8 @@
     "no_subject": "(Kein Betreff)",
     "no_body_content": "(Kein Inhalt verfügbar)",
     "no_preview_available": "Keine Vorschau verfügbar",
+    "show_quoted_text": "Zitierten Text anzeigen",
+    "hide_quoted_text": "Zitierten Text ausblenden",
     "loading_email": "E-Mail wird geladen...",
     "loading": "Lädt...",
     "reply": "Antworten",

locales/en/common.json

@@ -277,6 +277,8 @@
     "no_subject": "(No Subject)",
     "no_body_content": "(No body content available)",
     "no_preview_available": "No preview available",
+    "show_quoted_text": "Show quoted text",
+    "hide_quoted_text": "Hide quoted text",
     "loading_email": "Loading email...",
     "loading": "Loading...",
     "reply": "Reply",

locales/es/common.json

@@ -277,6 +277,8 @@
     "no_subject": "(Sin Asunto)",
     "no_body_content": "(Sin contenido disponible)",
     "no_preview_available": "Vista previa no disponible",
+    "show_quoted_text": "Mostrar texto citado",
+    "hide_quoted_text": "Ocultar texto citado",
     "loading_email": "Cargando correo...",
     "loading": "Cargando...",
     "reply": "Responder",

locales/fa/common.json

@@ -277,6 +277,8 @@
     "no_subject": "(بدون موضوع)",
     "no_body_content": "(محتوایی موجود نیست)",
     "no_preview_available": "پیش‌نمایشی در دسترس نیست",
+    "show_quoted_text": "نمایش متن نقل‌قول‌شده",
+    "hide_quoted_text": "پنهان کردن متن نقل‌قول‌شده",
     "loading_email": "در حال بارگذاری ایمیل...",
     "loading": "در حال بارگذاری...",
     "reply": "پاسخ",

locales/fr/common.json

@@ -277,6 +277,8 @@
     "no_subject": "(Sans objet)",
     "no_body_content": "(Aucun contenu disponible)",
     "no_preview_available": "Aucun aperçu disponible",
+    "show_quoted_text": "Afficher le texte cité",
+    "hide_quoted_text": "Masquer le texte cité",
     "loading_email": "Chargement de l'email...",
     "loading": "Chargement...",
     "reply": "Répondre",

locales/he/common.json

@@ -478,6 +478,8 @@
     },
     "no_body_content": "(אין תוכן גוף זמין)",
     "no_preview_available": "אין תצוגה מקדימה זמינה",
+    "show_quoted_text": "הצג טקסט מצוטט",
+    "hide_quoted_text": "הסתר טקסט מצוטט",
     "unread": "סמן כלא נקרא",
     "read": "קרא",
     "spam_short": "דואר זבל",

locales/hu/common.json

@@ -277,6 +277,8 @@
     "no_subject": "(Nincs tárgy)",
     "no_body_content": "(Nincs elérhető tartalom)",
     "no_preview_available": "Nincs előnézet",
+    "show_quoted_text": "Idézett szöveg megjelenítése",
+    "hide_quoted_text": "Idézett szöveg elrejtése",
     "loading_email": "E-mail betöltése...",
     "loading": "Betöltés...",
     "reply": "Válasz",

locales/it/common.json

@@ -277,6 +277,8 @@
     "no_subject": "(Nessun oggetto)",
     "no_body_content": "(Nessun contenuto disponibile)",
     "no_preview_available": "Anteprima non disponibile",
+    "show_quoted_text": "Mostra testo citato",
+    "hide_quoted_text": "Nascondi testo citato",
     "loading_email": "Caricamento messaggio...",
     "loading": "Caricamento...",
     "reply": "Rispondi",

locales/ja/common.json

@@ -277,6 +277,8 @@
     "no_subject": "（件名なし）",
     "no_body_content": "（本文がありません）",
     "no_preview_available": "プレビューは利用できません",
+    "show_quoted_text": "引用テキストを表示",
+    "hide_quoted_text": "引用テキストを非表示",
     "loading_email": "メールを読み込み中...",
     "loading": "読み込み中...",
     "reply": "返信",

locales/ko/common.json

@@ -277,6 +277,8 @@
     "no_subject": "(제목 없음)",
     "no_body_content": "(본문 내용 없음)",
     "no_preview_available": "미리 보기를 사용할 수 없습니다",
+    "show_quoted_text": "인용된 텍스트 표시",
+    "hide_quoted_text": "인용된 텍스트 숨기기",
     "loading_email": "메일을 불러오는 중...",
     "loading": "불러오는 중...",
     "reply": "답장",

locales/lv/common.json

@@ -277,6 +277,8 @@
     "no_subject": "(nav temata)",
     "no_body_content": "(nav satura)",
     "no_preview_available": "Priekšskatījums nav pieejams",
+    "show_quoted_text": "Rādīt citēto tekstu",
+    "hide_quoted_text": "Paslēpt citēto tekstu",
     "loading_email": "Ielādē vēstuli...",
     "loading": "Ielādē...",
     "reply": "Atbildēt",

locales/nl/common.json

@@ -277,6 +277,8 @@
     "no_subject": "(Geen onderwerp)",
     "no_body_content": "(Geen inhoud beschikbaar)",
     "no_preview_available": "Geen voorbeeld beschikbaar",
+    "show_quoted_text": "Geciteerde tekst tonen",
+    "hide_quoted_text": "Geciteerde tekst verbergen",
     "loading_email": "E-mail laden...",
     "loading": "Laden...",
     "reply": "Beantwoorden",

locales/pl/common.json

@@ -277,6 +277,8 @@
     "no_subject": "(Bez tematu)",
     "no_body_content": "(Brak treści)",
     "no_preview_available": "Podgląd niedostępny",
+    "show_quoted_text": "Pokaż cytowany tekst",
+    "hide_quoted_text": "Ukryj cytowany tekst",
     "loading_email": "Ładowanie wiadomości...",
     "loading": "Ładowanie...",
     "reply": "Odpowiedz",

locales/pt/common.json

@@ -277,6 +277,8 @@
     "no_subject": "(Sem Assunto)",
     "no_body_content": "(Sem conteúdo disponível)",
     "no_preview_available": "Pré-visualização não disponível",
+    "show_quoted_text": "Mostrar texto citado",
+    "hide_quoted_text": "Ocultar texto citado",
     "loading_email": "Carregando e-mail...",
     "loading": "Carregando...",
     "reply": "Responder",

locales/ro/common.json

@@ -277,6 +277,8 @@
     "no_subject": "(Fără subiect)",
     "no_body_content": "(Nu există conținut disponibil)",
     "no_preview_available": "Nu este disponibilă previzualizarea",
+    "show_quoted_text": "Afișează textul citat",
+    "hide_quoted_text": "Ascunde textul citat",
     "loading_email": "Se încarcă e-mailul...",
     "loading": "Se încarcă...",
     "reply": "Răspunde",

locales/ru/common.json

@@ -277,6 +277,8 @@
     "no_subject": "(Без темы)",
     "no_body_content": "(Содержимое отсутствует)",
     "no_preview_available": "Предварительный просмотр недоступен",
+    "show_quoted_text": "Показать цитируемый текст",
+    "hide_quoted_text": "Скрыть цитируемый текст",
     "loading_email": "Загрузка письма...",
     "loading": "Загрузка...",
     "reply": "Ответить",

locales/sk/common.json

@@ -277,6 +277,8 @@
     "no_subject": "(Bez predmetu)",
     "no_body_content": "(Obsah správy nie je dostupný)",
     "no_preview_available": "Náhľad nie je dostupný",
+    "show_quoted_text": "Zobraziť citovaný text",
+    "hide_quoted_text": "Skryť citovaný text",
     "loading_email": "Načítavanie e-mailu...",
     "loading": "Načítavanie...",
     "reply": "Odpovedať",

locales/tr/common.json

@@ -277,6 +277,8 @@
     "no_subject": "(Konu Yok)",
     "no_body_content": "(İçerik yok)",
     "no_preview_available": "Önizleme kullanılamıyor",
+    "show_quoted_text": "Alıntılanan metni göster",
+    "hide_quoted_text": "Alıntılanan metni gizle",
     "loading_email": "E-posta yükleniyor...",
     "loading": "Yükleniyor...",
     "reply": "Yanıtla",

locales/uk/common.json

@@ -277,6 +277,8 @@
     "no_subject": "(без теми)",
     "no_body_content": "(вміст відсутній)",
     "no_preview_available": "Попередній перегляд недоступний",
+    "show_quoted_text": "Показати цитований текст",
+    "hide_quoted_text": "Приховати цитований текст",
     "loading_email": "Завантаження електронної пошти...",
     "loading": "Завантаження...",
     "reply": "Відповісти",

locales/zh/common.json

@@ -277,6 +277,8 @@
     "no_subject": "（无主题）",
     "no_body_content": "（无正文内容）",
     "no_preview_available": "无可用预览",
+    "show_quoted_text": "显示引用文本",
+    "hide_quoted_text": "隐藏引用文本",
     "loading_email": "正在加载邮件...",
     "loading": "正在加载…",
     "reply": "回复",