fix: keep mail lines a readable length on wide screens

src/lib/__tests__/email-html.test.ts

@@ -8,6 +8,7 @@ import {
   hasRemoteContent,
   prepareEmailHtml,
   wrapPlainTextEmail,
+  wrapEmailHtml,
   hasNativeDarkMode,
   sniffImageMime,
   TRANSPARENT_BLOCKED_PIXEL,
@@ -253,3 +254,12 @@ describe('sniffImageMime', () => {
     expect(sniffImageMime(new Uint8Array([1, 2, 3]), 'application/octet-stream')).toBe('application/octet-stream');
   });
 });
+
+describe('reading width on a wide pane', () => {
+  it('caps HTML and plain-text bodies only above the tablet breakpoint', () => {
+    const html = wrapEmailHtml('<p>Hello</p>');
+    expect(html).toMatch(/@media \(min-width: 840px\) \{\s*body \{ max-width: 720px;/);
+    const plain = wrapPlainTextEmail('Hello');
+    expect(plain).toContain('@media (min-width: 840px) { body { max-width: 80ch; } }');
+  });
+});

src/lib/email-html.ts

@@ -449,6 +449,11 @@ body {
   word-wrap: break-word;
   overflow-wrap: break-word;
 }
+/* A wide reading pane (tablet): keep lines readable instead of running
+   150+ characters across. Phones never reach the breakpoint. */
+@media (min-width: 840px) {
+  body { max-width: 720px; margin-left: auto; margin-right: auto; }
+}
 /* Only force the cap on images and tables that set no max-width of their own:
    an !important 100% also overrides a sender's inline max-width, so an image
    sized by max-width + max-height + width:100% grows to the pane width while
@@ -676,7 +681,7 @@ export function wrapPlainTextEmail(
   const { isDark = true, font = 'sans' } = options;
   const cleaned = stripDangerousTags(innerHtml);
 
-  const bg = isDark ? '#09090b' : '#ffffff';
+  const bg = isDark ? '#0a0a0a' : '#ffffff';
   const fg = isDark ? '#fafafa' : '#1a1a1a';
   const link = isDark ? '#60a5fa' : '#1a73e8';
   const fontFamily = font === 'mono'
@@ -701,6 +706,8 @@ body {
 }
 a { color: ${link}; text-decoration: underline; }
 details > summary::-webkit-details-marker { display: none; }
+/* A wide reading pane (tablet): about 80 characters a line. */
+@media (min-width: 840px) { body { max-width: 80ch; } }
 `;
 
   return `<!doctype html>