fix: mark quotes and list items in the plain-text part of sent mail

components/email/email-composer.tsx

@@ -84,9 +84,10 @@ import { toUnicodeEmail } from "@/lib/idn";
  * Derives the text/plain alternative from the composer's HTML body, preserving
  * line structure from block elements and <br> tags. Paragraph spacing is on so
  * <p> blocks are separated by a blank line, matching their visual rendering (#421).
+ * Quotes get "> " and list items their markers, like any plain-text mail.
  */
 function htmlToPlainText(html: string): string {
-  return htmlToPlainTextShared(html, { paragraphSpacing: true });
+  return htmlToPlainTextShared(html, { paragraphSpacing: true, mailMarkup: true });
 }
 
 /**

lib/__tests__/html-to-text.test.ts

@@ -60,4 +60,28 @@ describe('htmlToPlainText', () => {
     // recognise as the start of a signature.
     expect(htmlToPlainText('<p>Hi</p><p>-- </p><p>User A</p>')).toBe('Hi\n-- \nUser A');
   });
+
+  describe('mailMarkup', () => {
+    // The text part of a reply showed the quoted original as ordinary text,
+    // and list items without their bullets.
+    const mail = { paragraphSpacing: true, mailMarkup: true };
+
+    it('prefixes quoted text with "> "', () => {
+      const html = '<p>Sure.</p><p>On Sun, B wrote:</p><div data-quoted-html=""><p>Hi A,</p><p>can you?</p></div>';
+      expect(htmlToPlainText(html, mail)).toBe('Sure.\n\nOn Sun, B wrote:\n\n> Hi A,\n>\n> can you?');
+    });
+
+    it('nests quotes', () => {
+      expect(htmlToPlainText('<blockquote><p>a</p><blockquote><p>b</p></blockquote></blockquote>', mail)).toBe('> a\n>\n> > b');
+    });
+
+    it('marks list items', () => {
+      expect(htmlToPlainText('<ul><li>Revenue</li><li>Costs</li></ul><ol start="3"><li>x</li><li>y</li></ol>', mail))
+        .toBe('- Revenue\n- Costs\n\n3. x\n4. y');
+    });
+
+    it('leaves the default conversion unchanged', () => {
+      expect(htmlToPlainText('<blockquote>a</blockquote><ul><li>b</li></ul>')).toBe('a\nb');
+    });
+  });
 });

lib/html-to-text.ts

@@ -55,6 +55,12 @@ export interface HtmlToPlainTextOptions {
    * are visually spaced; leave off for compact output like signatures.
    */
   paragraphSpacing?: boolean;
+  /**
+   * Mark quoted text (<blockquote>, the composer's quoted original) with "> "
+   * and list items with "- " or "1. ", as plain-text mail does. Without them
+   * the text part of a reply could not tell the reply from the quote.
+   */
+  mailMarkup?: boolean;
 }
 
 function normalizeLineBreaks(value: string): string {
@@ -76,7 +82,7 @@ function normalizeLineBreaks(value: string): string {
  * is the href. Used to derive the text/plain alternative of an HTML email.
  */
 export function htmlToPlainText(html: string, options: HtmlToPlainTextOptions = {}): string {
-  const { paragraphSpacing = false } = options;
+  const { paragraphSpacing = false, mailMarkup = false } = options;
   const document = parseHtmlSafely(html);
   const chunks: string[] = [];
 
@@ -152,6 +158,31 @@ export function htmlToPlainText(html: string, options: HtmlToPlainTextOptions =
     const separator = paragraphSpacing && PARAGRAPH_TAGS.has(tagName) ? 2 : 1;
     const isBlock = BLOCK_TAGS.has(tagName);
 
+    if (mailMarkup && (tagName === 'blockquote' || element.hasAttribute('data-quoted-html'))) {
+      const quoted = htmlToPlainText(element.innerHTML, options);
+      if (quoted) {
+        ensureNewlines(separator);
+        chunks.push(quoted.split('\n').map((line) => (line ? `> ${line}` : '>')).join('\n'));
+        ensureNewlines(separator);
+      }
+      return;
+    }
+
+    if (mailMarkup && tagName === 'li') {
+      const list = element.parentElement;
+      let marker = '- ';
+      if (list?.tagName.toLowerCase() === 'ol') {
+        const start = Number(list.getAttribute('start') ?? 1) || 1;
+        const position = Array.from(list.children).filter((child) => child.tagName.toLowerCase() === 'li').indexOf(element);
+        marker = `${start + position}. `;
+      }
+      ensureNewlines(1);
+      chunks.push(marker);
+      Array.from(element.childNodes).forEach(walk);
+      ensureNewlines(1);
+      return;
+    }
+
     if (isBlock) {
       ensureNewlines(separator);
     }