fix: keep list previews and subjects on one line

Previews keep the body's paragraph breaks, so a line-clamped row showed
a dangling "…" line and rows came out at uneven heights, and a subject
carrying CR/LF rendered over several lines in the list and the viewer.
Fold every whitespace run to a single space before display with a new
`singleLine` helper, in the mailbox and unified inbox rows, the viewer
subject and the collapsed thread card preview.

src/components/email/ThreadMessageCard.tsx

@@ -9,6 +9,7 @@ import { useLocaleStore } from '../../stores/locale-store';
 import SenderAvatar from '../SenderAvatar';
 import { MessageContent, type MessageContentProps } from './MessageContent';
 import { emailDisplayDate, formatHeaderDate, formatHeaderTime } from '../../lib/email-date';
+import { singleLine } from '../../lib/single-line';
 
 interface Props extends MessageContentProps {
   expanded: boolean;
@@ -45,7 +46,7 @@ export function ThreadMessageCard({ expanded, onToggleExpanded, onReply, ...cont
             {email.hasAttachment && <Paperclip size={12} color={c.textMuted} />}
             <Text style={styles.collapsedDate}>{formatHeaderDate(date, locale)} {formatHeaderTime(date, timeFormat, locale)}</Text>
           </View>
-          <Text style={styles.collapsedPreview} numberOfLines={1}>{email.preview || ''}</Text>
+          <Text style={styles.collapsedPreview} numberOfLines={1}>{singleLine(email.preview)}</Text>
         </View>
         {starred && <Star size={14} color={c.starred} fill={c.starred} />}
       </Pressable>

src/lib/__tests__/single-line.test.ts

@@ -0,0 +1,24 @@
+import { describe, it, expect } from 'vitest';
+import { singleLine } from '../single-line';
+
+describe('singleLine', () => {
+  it('folds preview paragraph breaks into single spaces', () => {
+    expect(singleLine('Q3 revenue is up 12 %.\n\n…')).toBe('Q3 revenue is up 12 %. …');
+    expect(singleLine('Hi team,\r\n\r\nthe numbers\tare in.  See below.\n')).toBe('Hi team, the numbers are in. See below.');
+  });
+
+  it('folds a subject carrying CR/LF onto one line', () => {
+    expect(singleLine('Invoice 1042\r\n for September')).toBe('Invoice 1042 for September');
+  });
+
+  it('returns an empty string for missing or blank input', () => {
+    expect(singleLine(undefined)).toBe('');
+    expect(singleLine(null)).toBe('');
+    expect(singleLine(' \r\n\t ')).toBe('');
+  });
+
+  it('keeps a lone no-break space but folds runs that contain one', () => {
+    expect(singleLine('12 %')).toBe('12 %');
+    expect(singleLine('a \nb')).toBe('a b');
+  });
+});

src/lib/single-line.ts

@@ -0,0 +1,12 @@
+/**
+ * Fold a server string onto one line for display: every run of whitespace
+ * (CR/LF, tabs, repeated spaces) becomes a single space and the ends are
+ * trimmed. Message previews keep the body's paragraph breaks and a subject
+ * can carry a stray CR/LF; on a line-clamped Text those left a dangling
+ * "…" line and uneven row heights, and an unclamped subject wrapped over
+ * several lines. A lone no-break space is kept so "12 %" doesn't split.
+ */
+export function singleLine(text: string | null | undefined): string {
+  if (!text) return '';
+  return text.replace(/\s+/g, (run) => (run === ' ' ? run : ' ')).trim();
+}

src/screens/EmailListScreen.tsx

@@ -31,6 +31,7 @@ import { useContactsStore } from '../stores/contacts-store';
 import { useOutboxStore } from '../stores/outbox-store';
 import { getContactDisplayName } from '../lib/contact-utils';
 import { formatListDate } from '../lib/date-format';
+import { singleLine } from '../lib/single-line';
 import {
   findTrashMailbox, findArchiveMailbox, findJunkMailbox, mailboxesForSiblingOf, ownMailboxes,
 } from '../lib/mailbox-tree';
@@ -210,7 +211,7 @@ const EmailRow = React.memo(function EmailRow({
         {/* Row 2: Subject + tag pills */}
         <View style={styles.subjectRow}>
           <Text style={[styles.emailSubject, dyn.body, unread && styles.textBold]} numberOfLines={1}>
-            {item.subject || '(no subject)'}
+            {singleLine(item.subject) || '(no subject)'}
           </Text>
           {tags.slice(0, 3).map((tag) => (
             <View key={tag.id} style={[styles.tagPill, { backgroundColor: tag.bg }]}>
@@ -226,7 +227,7 @@ const EmailRow = React.memo(function EmailRow({
         {/* Row 3: Preview - hidden in compact density modes regardless of toggle */}
         {showPreview && density.showPreview && (
           <Text style={[styles.emailPreview, dyn.body]} numberOfLines={2}>
-            {item.preview}
+            {singleLine(item.preview)}
           </Text>
         )}
       </View>

src/screens/EmailThreadScreen.tsx

@@ -33,6 +33,7 @@ import { useSheetDrag } from '../lib/use-sheet-drag';
 import { useLocaleStore } from '../stores/locale-store';
 import { findTrashMailbox, mailboxesForSiblingOf } from '../lib/mailbox-tree';
 import { pickEmailBody, plainTextBody } from '../lib/email-body';
+import { singleLine } from '../lib/single-line';
 import { buildForwardAsAttachmentPayload } from '../lib/forward-as-attachment';
 import type { Email, EmailAddress, Identity } from '../api/types';
 import type { RootStackParamList } from '../navigation/types';
@@ -876,7 +877,7 @@ function EmailPane({
     return <EmailPaneSkeleton styles={styles} />;
   }
 
-  const subject = email.subject || t('email_viewer.no_subject', '(No Subject)');
+  const subject = singleLine(email.subject) || t('email_viewer.no_subject', '(No Subject)');
   const conversation = threading && threadIds && threadIds.length > 1
     ? threadIds.map((mid) => detailCache.get(mid)).filter((m): m is Email => !!m)
     : null;

src/screens/UnifiedInboxScreen.tsx

@@ -21,6 +21,7 @@ import { useAuthStore } from '../stores/auth-store';
 import { useSettingsStore, type SwipeAction } from '../stores/settings-store';
 import { useLocaleStore } from '../stores/locale-store';
 import { formatListDate } from '../lib/date-format';
+import { singleLine } from '../lib/single-line';
 import { isPermanentDelete, confirmPermanentDelete } from '../lib/delete-confirm';
 import { spacing, typography, componentSizes, radius, type ThemePalette } from '../theme/tokens';
 import { useColors } from '../theme/colors';
@@ -319,7 +320,7 @@ export default function UnifiedInboxScreen({ navigation, route }: Props) {
               <Text style={styles.time}>{formatListDate(item.receivedAt, { dateFormat, timeFormat, locale, t })}</Text>
             </View>
             <Text style={[styles.subject, unread && styles.bold]} numberOfLines={1}>
-              {item.subject || '(no subject)'}
+              {singleLine(item.subject) || '(no subject)'}
             </Text>
             <View style={styles.line}>
               {acc && accountIds.length > 1 && (
@@ -342,7 +343,7 @@ export default function UnifiedInboxScreen({ navigation, route }: Props) {
               )}
             </View>
             {item.preview ? (
-              <Text style={styles.preview} numberOfLines={1}>{item.preview}</Text>
+              <Text style={styles.preview} numberOfLines={1}>{singleLine(item.preview)}</Text>
             ) : null}
           </View>
         </Pressable>