diff --git a/App.tsx b/App.tsx
index bc631fa8..31b0ddc7 100644
--- a/App.tsx
+++ b/App.tsx
@@ -58,10 +58,11 @@ import { useCalendarStore } from './src/stores/calendar-store';
 import { useContactsStore } from './src/stores/contacts-store';
 import { useEmailStore, viewerParamsForRow } from './src/stores/email-store';
 import { mailboxAccountId } from './src/lib/mailbox-tree';
-import { prefetchMessage } from './src/lib/email-detail-cache';
+import { loadDetail, prefetchMessage } from './src/lib/email-detail-cache';
 import { useHasCalendar, useHasContacts, useHasFiles } from './src/lib/capabilities';
 import { useSettingsStore } from './src/stores/settings-store';
 import { useLocaleStore } from './src/stores/locale-store';
+import { toast } from './src/stores/toast-store';
 import { useNetworkStore } from './src/stores/network-store';
 import { useUpdatesStore } from './src/stores/updates-store';
 import { UpdateBanner } from './src/components/UpdateBanner';
@@ -69,10 +70,9 @@ import { PushOnboardingPrompt } from './src/components/PushOnboardingPrompt';
 import { ToastHost } from './src/components/ToastHost';
 import { UndoSnackbar } from './src/components/UndoSnackbar';
 import { AppIconBadge } from './src/components/AppIconBadge';
-import { getEmails, getFullEmail } from './src/api/email';
+import { getEmails } from './src/api/email';
 import { signOutWidgets, startWidgetSync } from './src/widgets/sync';
 import { draftContextFromEmail } from './src/lib/draft-context';
-import { replyComposeParams } from './src/lib/reply-compose';
 import { handleDeepLink, parseDeepLink, shareToDeepLink, type DeepLink } from './src/navigation/linking';
 import { addShareListener, getInitialShare, shareAttachments } from './src/lib/share-intent';
 import { OfflineCacheBanner } from './src/components/OfflineCacheBanner';
@@ -134,7 +134,7 @@ async function openCalendarReminder(target: CalendarReminderTarget): Promise<voi
 // Deep links (bulwarkmobile://, webmail https permalinks, mailto:) and
 // Android share-sheet payloads all end up here once the navigator is ready.
 async function openDeepLink(link: DeepLink): Promise<void> {
-  await handleDeepLink(link, {
+  const opened = await handleDeepLink(link, {
     navigation: navigationRef,
     resolveThreadId: async (emailId, jmapAccountId) => {
       try {
@@ -144,19 +144,10 @@ async function openDeepLink(link: DeepLink): Promise<void> {
         return null;
       }
     },
-    openReply: async (emailId, jmapAccountId) => {
-      try {
-        const params = replyComposeParams('reply', await getFullEmail(emailId, jmapAccountId), jmapAccountId);
-        if (!params || !navigationRef.isReady()) return false;
-        navigationRef.navigate('Compose', params);
-        return true;
-      } catch {
-        return false;
-      }
-    },
     openDraft: async (emailId, jmapAccountId) => {
       try {
-        const draft = draftContextFromEmail(await getFullEmail(emailId, jmapAccountId), jmapAccountId);
+        // Cache first, so a draft read before still opens offline.
+        const draft = draftContextFromEmail(await loadDetail(emailId, jmapAccountId), jmapAccountId);
         if (!navigationRef.isReady()) return false;
         navigationRef.navigate('Compose', { draft });
         return true;
@@ -172,6 +163,9 @@ async function openDeepLink(link: DeepLink): Promise<void> {
       return useAuthStore.getState().activeAccountId === accountId;
     },
   });
+  // A widget or a link elsewhere brought the app up for this; say it failed
+  // rather than leave the user wondering why the app just opened.
+  if (!opened) toast.error(useLocaleStore.getState().t('deep_link.open_failed', "Couldn't open this"));
 }
 
 // Toasts and the undo bar show on whichever stack screen is up, so a failure
diff --git a/locales/rn/en.json b/locales/rn/en.json
index cabbed7d..b6c558d8 100644
--- a/locales/rn/en.json
+++ b/locales/rn/en.json
@@ -249,6 +249,9 @@
     "color_tag": "Tag",
     "remove_color": "Remove tag"
   },
+  "deep_link": {
+    "open_failed": "Couldn't open this"
+  },
   "email_composer": {
     "attach_camera": "Camera",
     "attachment_reminder_body": "Your message mentions \"{keyword}\" but no file is attached. Send anyway?",
diff --git a/src/navigation/__tests__/linking.test.ts b/src/navigation/__tests__/linking.test.ts
index a701f962..3468282b 100644
--- a/src/navigation/__tests__/linking.test.ts
+++ b/src/navigation/__tests__/linking.test.ts
@@ -3,6 +3,7 @@ import { handleDeepLink, parseDeepLink, shareToDeepLink } from '../linking';
 import { usePendingSettingsTab } from '../pending-settings-tab';
 import { usePendingCalendarOpen } from '../pending-calendar-open';
 import { usePendingMailSearch } from '../pending-mail-search';
+import { links } from '../../widgets/clicks';
 
 describe('parseDeepLink', () => {
   it('parses app-scheme mail links', () => {
@@ -80,6 +81,14 @@ describe('parseDeepLink', () => {
     expect(parseDeepLink('bulwarkmobile://mail/message/M1?account=a%40b&jmapAccount=team&action=reply')).toEqual({
       kind: 'message', emailId: 'M1', accountId: 'a@b', jmapAccountId: 'team', action: 'reply',
     });
+    // What the widgets build is what the app reads, thread included.
+    const m = { id: 'M/1', threadId: 'T1', accountId: 'a@b', jmapAccountId: 'team' };
+    expect(parseDeepLink(links.reply(m))).toEqual({
+      kind: 'message', emailId: 'M/1', accountId: 'a@b', jmapAccountId: 'team', threadId: 'T1', action: 'reply',
+    });
+    expect(parseDeepLink(links.message({ id: 'M2', accountId: 'a@b' }))).toEqual({
+      kind: 'message', emailId: 'M2', accountId: 'a@b',
+    });
     expect(parseDeepLink('bulwarkmobile://mail/draft/D1')).toEqual({ kind: 'draft', emailId: 'D1', accountId: undefined });
     expect(parseDeepLink('bulwarkmobile://mail/unified?view=starred')).toEqual({ kind: 'unified', view: 'starred' });
     expect(parseDeepLink('bulwarkmobile://mail/unified?role=drafts&view=bogus')).toEqual({ kind: 'unified', role: 'drafts' });
@@ -179,7 +188,7 @@ describe('handleDeepLink', () => {
     }));
   });
 
-  it('opens a group-mailbox message in its JMAP account and hands replies to the composer opener', async () => {
+  it('opens a group-mailbox message in its JMAP account', async () => {
     const navigation = nav();
     const resolveThreadId = vi.fn(async () => 'T1');
     await handleDeepLink(
@@ -188,14 +197,25 @@ describe('handleDeepLink', () => {
     );
     expect(resolveThreadId).toHaveBeenCalledWith('M1', 'team');
     expect(navigation.navigate).toHaveBeenCalledWith('EmailThread', { emailId: 'M1', threadId: 'T1', jmapAccountId: 'team' });
+  });
 
-    const openReply = vi.fn(async () => true);
+  it('opens a reply over its message, without a lookup when the link names the thread', async () => {
+    // Offline, or before the session is back: the lookup would fail.
+    const resolveThreadId = vi.fn(async () => null);
+    const navigation = nav();
     const ok = await handleDeepLink(
-      { kind: 'message', emailId: 'M2', action: 'reply' },
-      { navigation: nav() as never, resolveThreadId, openReply },
+      { kind: 'message', emailId: 'M2', threadId: 'T2', action: 'reply' },
+      { navigation: navigation as never, resolveThreadId },
     );
     expect(ok).toBe(true);
-    expect(openReply).toHaveBeenCalledWith('M2', undefined);
+    expect(resolveThreadId).not.toHaveBeenCalled();
+    expect(navigation.navigate).toHaveBeenCalledWith('EmailThread', { emailId: 'M2', threadId: 'T2', action: 'reply' });
+
+    // Without the thread and without a server, nothing opens (the app says so).
+    expect(await handleDeepLink(
+      { kind: 'message', emailId: 'M3', action: 'reply' },
+      { navigation: nav() as never, resolveThreadId },
+    )).toBe(false);
   });
 
   it('opens drafts, unified views, scheduled mail and searches', async () => {
diff --git a/src/navigation/linking.ts b/src/navigation/linking.ts
index 9149f94d..537b48e0 100644
--- a/src/navigation/linking.ts
+++ b/src/navigation/linking.ts
@@ -19,8 +19,9 @@ type UnifiedView = typeof UNIFIED_VIEWS[number];
 
 export type DeepLink =
   // `jmapAccountId`: the JMAP account owning a message in a group/shared
-  // mailbox (`?jmapAccount=`); `action: 'reply'` opens a reply to it.
-  | { kind: 'message'; emailId: string; accountId?: string; jmapAccountId?: string; action?: 'reply' }
+  // mailbox (`?jmapAccount=`); `threadId` (`?thread=`) saves looking it up;
+  // `action: 'reply'` opens a reply to it.
+  | { kind: 'message'; emailId: string; accountId?: string; jmapAccountId?: string; threadId?: string; action?: 'reply' }
   | { kind: 'draft'; emailId: string; accountId?: string; jmapAccountId?: string }
   | { kind: 'thread'; threadId: string; accountId?: string }
   | { kind: 'folder'; ref: string; accountId?: string }
@@ -96,11 +97,13 @@ export function parseDeepLink(url: string): DeepLink | null {
     case 'mail': {
       const jmapAccountId = search.get('jmapAccount') ?? undefined;
       if (kind === 'message' && value) {
+        const threadId = search.get('thread');
         return {
           kind: 'message',
           emailId: decodeSegment(value),
           accountId,
           ...(jmapAccountId ? { jmapAccountId } : {}),
+          ...(threadId ? { threadId } : {}),
           ...(search.get('action') === 'reply' ? { action: 'reply' as const } : {}),
         };
       }
@@ -169,9 +172,8 @@ export interface DeepLinkNavigator {
   // null when the message cannot be loaded. `jmapAccountId` names the
   // group/shared account holding it, when it is not the user's own.
   resolveThreadId: (emailId: string, jmapAccountId?: string) => Promise<string | null>;
-  // Open the composer on a reply to / on a server draft of this message.
-  // Resolve false when the message cannot be loaded.
-  openReply?: (emailId: string, jmapAccountId?: string) => Promise<boolean>;
+  // Open the composer on a server draft. Resolve false when the draft cannot
+  // be loaded.
   openDraft?: (emailId: string, jmapAccountId?: string) => Promise<boolean>;
   // Switch to the account a permalink names (`?account=`); resolves false
   // when that account is not signed in on this device.
@@ -189,15 +191,16 @@ export async function handleDeepLink(link: DeepLink, nav: DeepLinkNavigator): Pr
 
   switch (link.kind) {
     case 'message': {
-      if (link.action === 'reply' && nav.openReply) {
-        return nav.openReply(link.emailId, link.jmapAccountId);
-      }
-      const threadId = await nav.resolveThreadId(link.emailId, link.jmapAccountId);
+      const threadId = link.threadId ?? await nav.resolveThreadId(link.emailId, link.jmapAccountId);
       if (!threadId) return false;
+      // A reply opens over the message, like the reader's own Reply: the
+      // reader loads it (from its cache when offline) and then opens the
+      // composer, or shows why it could not.
       navigation.navigate('EmailThread', {
         emailId: link.emailId,
         threadId,
         ...(link.jmapAccountId ? { jmapAccountId: link.jmapAccountId } : {}),
+        ...(link.action === 'reply' ? { action: 'reply' as const } : {}),
       });
       return true;
     }
diff --git a/src/navigation/types.ts b/src/navigation/types.ts
index 3ed53acb..098f7c8f 100644
--- a/src/navigation/types.ts
+++ b/src/navigation/types.ts
@@ -67,6 +67,8 @@ export type RootStackParamList = {
      * viewer pages over the store's current folder.
      */
     emailIds?: string[];
+    /** Open the composer on a reply once the message has loaded (widget Reply). */
+    action?: 'reply';
   };
   EmailSource: { emailId: string; blobId: string; subject?: string; jmapAccountId?: string };
   Compose:
diff --git a/src/screens/EmailThreadScreen.tsx b/src/screens/EmailThreadScreen.tsx
index 747213a3..aad8f3f9 100644
--- a/src/screens/EmailThreadScreen.tsx
+++ b/src/screens/EmailThreadScreen.tsx
@@ -536,6 +536,15 @@ function EmailViewer({ route, navigation }: Props) {
     if (params) navigation.navigate('Compose', params);
   }, [email, navigation, ownerAccountId]);
 
+  // Opened to reply (a widget's Reply): the composer follows as soon as the
+  // message is here, once. If it never loads, the reader's error says why.
+  const replyPending = React.useRef(route.params.action === 'reply');
+  React.useEffect(() => {
+    if (!replyPending.current || email?.id !== route.params.emailId) return;
+    replyPending.current = false;
+    navigateCompose('reply', email);
+  }, [email, route.params.emailId, navigateCompose]);
+
   // Forward the raw message as a message/rfc822 attachment (webmail 1.8.1).
   const onForwardAsAttachment = () => {
     setMoreMenuOpen(false);
diff --git a/src/widgets/clicks.ts b/src/widgets/clicks.ts
index b88f2a6c..838f21c9 100644
--- a/src/widgets/clicks.ts
+++ b/src/widgets/clicks.ts
@@ -37,12 +37,16 @@ function query(params: Record<string, string | undefined>): string {
   return parts.length ? `?${parts.join('&')}` : '';
 }
 
+// Message links carry the thread so the app opens them without asking the
+// server first, which also works offline from its cache.
+type MessageRef = Pick<MailItem, 'id' | 'accountId' | 'jmapAccountId'> & { threadId?: string };
+
 export const links = {
   inbox: () => `${base}mail/folder/inbox`,
-  message: (m: Pick<MailItem, 'id' | 'accountId' | 'jmapAccountId'>) =>
-    `${base}mail/message/${enc(m.id)}${query({ account: m.accountId, jmapAccount: m.jmapAccountId })}`,
-  reply: (m: Pick<MailItem, 'id' | 'accountId' | 'jmapAccountId'>) =>
-    `${base}mail/message/${enc(m.id)}${query({ account: m.accountId, jmapAccount: m.jmapAccountId, action: 'reply' })}`,
+  message: (m: MessageRef) =>
+    `${base}mail/message/${enc(m.id)}${query({ account: m.accountId, jmapAccount: m.jmapAccountId, thread: m.threadId })}`,
+  reply: (m: MessageRef) =>
+    `${base}mail/message/${enc(m.id)}${query({ account: m.accountId, jmapAccount: m.jmapAccountId, thread: m.threadId, action: 'reply' })}`,
   draft: (m: Pick<MailItem, 'id' | 'accountId' | 'jmapAccountId'>) =>
     `${base}mail/draft/${enc(m.id)}${query({ account: m.accountId, jmapAccount: m.jmapAccountId })}`,
   unified: (params: { view?: 'all' | 'unread' | 'starred'; role?: string } = {}) =>
diff --git a/src/widgets/jmap.ts b/src/widgets/jmap.ts
index 1891802c..52ddd260 100644
--- a/src/widgets/jmap.ts
+++ b/src/widgets/jmap.ts
@@ -184,7 +184,7 @@ export async function fetchMailSection(
     calls.push(['Email/get', {
       accountId,
       '#ids': { resultOf: 'qa', name: 'Email/query', path: '/ids' },
-      properties: ['id', 'from', 'receivedAt', 'attachments'],
+      properties: ['id', 'threadId', 'from', 'receivedAt', 'attachments'],
       bodyProperties: ['name', 'type', 'disposition', 'cid', 'size'],
     }, 'ga']);
   }
@@ -221,6 +221,7 @@ export async function fetchMailSection(
   }>)
     .map((e) => ({
       emailId: e.id,
+      threadId: e.threadId,
       accountId: registryAccountId,
       fromName: e.from?.[0]?.name || e.from?.[0]?.email || '',
       receivedAt: Date.parse(e.receivedAt) || 0,
diff --git a/src/widgets/layouts/hubs.tsx b/src/widgets/layouts/hubs.tsx
index b205a6ce..71bc13be 100644
--- a/src/widgets/layouts/hubs.tsx
+++ b/src/widgets/layouts/hubs.tsx
@@ -616,7 +616,7 @@ export const AttachmentsLayout: Layout = ({ s, p, f, now, width, height }) => {
         return (
           <FlexWidget
             key={g.emailId}
-            {...open(links.message({ id: g.emailId, accountId: g.accountId }))}
+            {...open(links.message({ id: g.emailId, threadId: g.threadId, accountId: g.accountId }))}
             style={{
               width: 'match_parent',
               paddingHorizontal: 14,
diff --git a/src/widgets/sample-snapshot.ts b/src/widgets/sample-snapshot.ts
index 640c30b7..e8bd4b70 100644
--- a/src/widgets/sample-snapshot.ts
+++ b/src/widgets/sample-snapshot.ts
@@ -157,9 +157,9 @@ export function sampleSnapshot(now: number): WidgetSnapshot {
       recentSearches: ['from:sarah', 'invoice', 'has:attachment', 'Q4 timeline', 'is:unread'],
       tags: [{ keyword: '$label:receipts', name: 'Receipts', color: '#f97316', unread: 2, total: 14, latestFrom: 'Sarah Kim', latestAt: ago(46) }],
       attachments: [
-        { emailId: 'm2', accountId: 'demo@example.com@demo', fromName: 'Sarah Kim', receivedAt: ago(46),
+        { emailId: 'm2', threadId: 't-m2', accountId: 'demo@example.com@demo', fromName: 'Sarah Kim', receivedAt: ago(46),
           files: [{ name: 'Invoice-2024-089.pdf', type: 'application/pdf' }, { name: 'prototype-v3.png', type: 'image/png' }] },
-        { emailId: 'm7', accountId: 'demo@example.com@demo', fromName: 'Anna Kowalski', receivedAt: ago(60 * 48),
+        { emailId: 'm7', threadId: 't-m7', accountId: 'demo@example.com@demo', fromName: 'Anna Kowalski', receivedAt: ago(60 * 48),
           files: [{ name: 'wedding-001.jpg', type: 'image/jpeg' }, { name: 'wedding-014.jpg', type: 'image/jpeg' }, { name: 'wedding-038.jpg', type: 'image/jpeg' }] },
       ],
     },
diff --git a/src/widgets/snapshot.ts b/src/widgets/snapshot.ts
index f9bf9f09..8e8e1b70 100644
--- a/src/widgets/snapshot.ts
+++ b/src/widgets/snapshot.ts
@@ -75,6 +75,8 @@ export interface TagCount {
 
 export interface AttachmentGroup {
   emailId: string;
+  /** Absent in snapshots stored before it was kept. */
+  threadId?: string;
   accountId: string;
   fromName: string;
   receivedAt: number;