fix: route conversation blobs by originating message

2026-10-31 00:12:39 +00:00 · 2026-10-19 15:43:38 +03:00
parent 391ed6c018
commit a73ac09035
5 changed files with 404 additions and 81 deletions
@@ -107,7 +107,7 @@ import { useDeviceDetection } from "@/hooks/use-media-query";
 import { useIsPaneScoped } from "@/hooks/use-pane-context";
 import { useAuthStore } from "@/stores/auth-store";
 import { useAccountStore } from "@/stores/account-store";
-import { useEmailStore } from "@/stores/email-store";
+import { useEmailStore, resolveEmailBlobContext, type EmailBlobContext } from "@/stores/email-store";
 import { useThemeStore } from "@/stores/theme-store";
 import { EmailIdentityBadge } from "./email-identity-badge";
 import { UnsubscribeBanner } from "./unsubscribe-banner";
@@ -129,7 +129,7 @@ import { parseTnef, isTnefAttachment } from "@/lib/tnef";
 import { debug } from "@/lib/debug";
 import { findVerificationCode, verificationCodeBodyText } from "@/lib/verification-code";
 import { VerificationCodeChip } from "./verification-code-chip";
-import { ConversationEmailBody, useConversationExternalContent, useMarkReadWhenShown } from "./thread-conversation-view";
+import { ConversationEmailBody, type ConversationAttachmentHandler, useConversationExternalContent, useMarkReadWhenShown } from "./thread-conversation-view";
 import type { TnefAttachment } from "@/lib/tnef";
 import { PluginSlot } from "@/components/plugins/plugin-slot";
 import { PluginActions } from "@/components/plugins/plugin-actions";
@@ -154,7 +154,7 @@ const SUB_MENU_ITEM_SELECTOR = '[role="menuitem"],[role="menuitemcheckbox"],[rol
 interface EmailViewerProps {
  email: Email | null;
  /** Captured message routing supplied by the standard mail UI. */
-  blobSource?: { client: IJMAPClient | null; accountId?: string };
+  blobSource?: EmailBlobContext;
  isLoading?: boolean;
  onReply?: (draftText?: string) => void;
  onReplyAll?: () => void;
@@ -165,7 +165,7 @@ interface EmailViewerProps {
  onToggleStar?: () => void;
  onMarkAsRead?: (emailId: string, read: boolean) => void;
  onSetTag?: (emailId: string, tagId: string | null) => void;
-  onDownloadAttachment?: (blobId: string, name: string, type?: string, forceDownload?: boolean) => void;
+  onDownloadAttachment?: (blobId: string, name: string, type?: string, forceDownload?: boolean, source?: EmailBlobContext) => void;
  onQuickReply?: (body: string) => Promise<void>;
  onMarkAsSpam?: () => void;
  onUndoSpam?: () => void;
@@ -791,6 +791,7 @@ export function MvExpandedConversationCard({
  onMarkRead,
  onReply,
  onDownloadAttachment,
+  blobSource,
  compact,
 }: {
  email: Email;
@@ -800,7 +801,8 @@ export function MvExpandedConversationCard({
  onLoadBody?: (email: Email) => void;
  onMarkRead?: (email: Email) => void;
  onReply?: (email: Email) => void;
-  onDownloadAttachment?: (blobId: string, name: string, type?: string) => void;
+  onDownloadAttachment?: ConversationAttachmentHandler;
+  blobSource?: EmailBlobContext;
 }) {
  const t = useTranslations('email_viewer');
  const externalContent = useConversationExternalContent();
@@ -883,6 +885,7 @@ export function MvExpandedConversationCard({
          onAllowExternal={() => externalContent.allow(email.id)}
          onTrustSender={externalContent.trustSender(email)}
          onDownloadAttachment={onDownloadAttachment}
+          blobSource={blobSource}
          className={cn("pb-4", compact ? "px-4" : "ps-[80px] pe-6")}
          bodyStyle={{ paddingBlock: '0.25rem 0.5rem' }}
        />
@@ -1215,7 +1218,10 @@ export function EmailViewer({
      onLoadBody={onLoadConversationEmail}
      onMarkRead={onMarkConversationEmailRead}
      onReply={onReplyConversationEmail}
-      onDownloadAttachment={onDownloadAttachment}
+      blobSource={target.sourceClientAccountId || target.sourceAccountId
+        ? resolveEmailBlobContext(target, client)
+        : blobSource ?? resolveEmailBlobContext(target, client)}
+      onDownloadAttachment={(blobId, name, type, source) => onDownloadAttachment?.(blobId, name, type, false, source)}
      compact={mvMobileViewer}
    />
  );
@@ -39,6 +39,7 @@ import {
 import { useTranslations } from "next-intl";
 import { useSettingsStore } from "@/stores/settings-store";
 import { useContactStore } from "@/stores/contact-store";
+import { useEmailStore, resolveEmailBlobContext, type EmailBlobContext } from "@/stores/email-store";
 import { useAuthStore } from "@/stores/auth-store";
 import { isFilePreviewable, toInertBlob } from "@/lib/file-preview";
 import { useWopiStatus, canWopiOpen } from "@/hooks/use-wopi-status";
@@ -51,6 +52,10 @@ import { usePluginRenderedBody } from "@/hooks/use-plugin-rendered-body";
 import { emailToReadView } from "@/lib/plugin-projection";
 import { AttachmentPluginMenu, ReaderAboveQuoteSlot } from "./reader-plugin-surfaces";

+export type ConversationAttachmentHandler = (
+  blobId: string, name: string, type: string | undefined, source: EmailBlobContext,
+) => void;
+
 interface ThreadConversationViewProps {
  thread: ThreadGroup;
  emails: Email[];
@@ -59,7 +64,9 @@ interface ThreadConversationViewProps {
  onReply?: (email: Email) => void;
  onReplyAll?: (email: Email) => void;
  onForward?: (email: Email) => void;
-  onDownloadAttachment?: (blobId: string, name: string, type?: string) => void;
+  onDownloadAttachment?: ConversationAttachmentHandler;
+  /** Routing captured when this conversation was opened. */
+  blobSource?: EmailBlobContext;
  onMarkAsRead?: (emailId: string, read: boolean) => void;
  /** Role of the folder the conversation was opened from, for plugin actions limited to some folders. */
  mailboxRole?: string | null;
@@ -176,6 +183,7 @@ export function ThreadConversationView({
  onReplyAll,
  onForward,
  onDownloadAttachment,
+  blobSource,
  onMarkAsRead,
  mailboxRole,
 }: ThreadConversationViewProps) {
@@ -274,6 +282,7 @@ export function ThreadConversationView({
              onReplyAll={onReplyAll ? () => onReplyAll(email) : undefined}
              onForward={onForward ? () => onForward(email) : undefined}
              onDownloadAttachment={onDownloadAttachment}
+            blobSource={blobSource}
              onMarkAsRead={onMarkAsRead}
              mailboxRole={mailboxRole}
            />
@@ -296,7 +305,9 @@ interface EmailCardProps {
  onReply?: () => void;
  onReplyAll?: () => void;
  onForward?: () => void;
-  onDownloadAttachment?: (blobId: string, name: string, type?: string) => void;
+  onDownloadAttachment?: ConversationAttachmentHandler;
+  /** Routing captured when this conversation was opened. */
+  blobSource?: EmailBlobContext;
  onMarkAsRead?: (emailId: string, read: boolean) => void;
  mailboxRole?: string | null;
 }
@@ -330,6 +341,7 @@ function EmailCard({
  onReplyAll,
  onForward,
  onDownloadAttachment,
+  blobSource,
  onMarkAsRead,
  mailboxRole,
 }: EmailCardProps) {
@@ -412,6 +424,7 @@ function EmailCard({
            onAllowExternal={onAllowExternal}
            onTrustSender={onTrustSender}
            onDownloadAttachment={onDownloadAttachment}
+            blobSource={blobSource}
          />
          <PluginSlot name="email-footer" className="w-full" extraProps={plugin.idProps} />

@@ -479,7 +492,9 @@ interface ConversationEmailBodyProps {
  allowExternal: boolean;
  onAllowExternal: () => void;
  onTrustSender?: () => void;
-  onDownloadAttachment?: (blobId: string, name: string, type?: string) => void;
+  onDownloadAttachment?: ConversationAttachmentHandler;
+  /** Routing captured when this conversation was opened. */
+  blobSource?: EmailBlobContext;
  /** Padding around the body; the phone card's density padding by default. */
  bodyStyle?: React.CSSProperties;
  className?: string;
@@ -496,6 +511,7 @@ export function ConversationEmailBody({
  onAllowExternal,
  onTrustSender,
  onDownloadAttachment,
+  blobSource,
  bodyStyle,
  className,
 }: ConversationEmailBodyProps) {
@@ -515,8 +531,18 @@ export function ConversationEmailBody({
    [showVerificationCodes, email.id, email.subject, email.bodyValues],
  );
  const [hasBlockedContent, setHasBlockedContent] = useState(false);
-  const [cidBlobUrls, setCidBlobUrls] = useState<Record<string, string>>({});
-  const { client } = useAuthStore(useShallow((state) => ({ client: state.client })));
+  const { client } = useAuthStore(useShallow((state) => ({
+    client: state.client, revision: state.connectedAccountsRevision,
+  })));
+  const fallbackSource = useEmailStore(useShallow(() => resolveEmailBlobContext(email, client)));
+  const source = blobSource ?? fallbackSource;
+  const { client: blobClient, accountId } = source;
+  // Local CID URLs belong to a particular client/owner/message/part list.
+  // Hide the previous set during render, before the new fetch's effect runs.
+  const cidRequest = useMemo(() => ({ blobClient, accountId, emailId: email.id, attachments: email.attachments }),
+    [blobClient, accountId, email.id, email.attachments]);
+  const [cidResult, setCidResult] = useState<{ request: typeof cidRequest; urls: Record<string, string> } | null>(null);
+  const cidBlobUrls = useMemo(() => cidResult?.request === cidRequest ? cidResult.urls : {}, [cidResult, cidRequest]);
  // A crypto plugin's decrypted body (PGP, S/MIME) replaces the message's own.
  const pluginBody = usePluginRenderedBody(email);
  // reader-above-quote: the body the quote was collapsed in, once it is on screen.
@@ -530,14 +556,14 @@ export function ConversationEmailBody({

  // Fetch inline CID images with authentication to prevent browser auth dialogs
  useEffect(() => {
-    if (!client || !email?.attachments) {
-      setCidBlobUrls({});
+    if (!blobClient || !cidRequest.attachments) {
+      setCidResult(null);
      return;
    }

-    const cidAttachments = email.attachments.filter(att => att.cid && att.blobId);
+    const cidAttachments = cidRequest.attachments.filter(att => att.cid && att.blobId);
    if (cidAttachments.length === 0) {
-      setCidBlobUrls({});
+      setCidResult(null);
      return;
    }

@@ -551,7 +577,7 @@ export function ConversationEmailBody({
        try {
          // Re-type sender-declared script-bearing parts before they become a
          // blob: URL in our origin (GHSA-xvjh-v9c6-qcvc).
-          const objectUrl = URL.createObjectURL(toInertBlob(await client!.fetchBlob(att.blobId, att.name || 'inline', att.type)));
+          const objectUrl = URL.createObjectURL(toInertBlob(await blobClient!.fetchBlob(att.blobId, att.name || 'inline', att.type, accountId)));
          if (!cancelled) {
            urls[cidValue] = objectUrl;
            objectUrls.push(objectUrl);
@@ -563,7 +589,7 @@ export function ConversationEmailBody({
        }
      }));
      if (!cancelled) {
-        setCidBlobUrls(urls);
+        setCidResult({ request: cidRequest, urls });
      }
    }

@@ -573,7 +599,7 @@ export function ConversationEmailBody({
      cancelled = true;
      objectUrls.forEach(url => URL.revokeObjectURL(url));
    };
-  }, [client, email?.id, email?.attachments]);
+  }, [cidRequest, blobClient, accountId]);

  // Sanitize and prepare email HTML content
  const emailContent = useMemo(() => {
@@ -867,7 +893,7 @@ export function ConversationEmailBody({
                <button
                  onClick={(e) => {
                    e.stopPropagation();
-                    onDownloadAttachment?.(attachment.blobId, attachment.name || 'attachment', attachment.type);
+                    onDownloadAttachment?.(attachment.blobId, attachment.name || 'attachment', attachment.type, source);
                  }}
                  title={opensPreview ? t('files.preview') : t('email_viewer.download')}
                  className="flex items-center gap-2 px-3 py-2 rounded-lg bg-muted hover:bg-muted/80 transition-colors text-sm"
@@ -1,7 +1,7 @@
 import React, { Suspense, lazy } from 'react';
-import { act, fireEvent, render, screen, waitFor } from '@testing-library/react';
+import { act, fireEvent, render, screen, waitFor, within } from '@testing-library/react';
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
-import type { Email, Mailbox } from '@/lib/jmap/types';
+import type { Email, Mailbox, ThreadGroup } from '@/lib/jmap/types';
 import { JMAPClient } from '@/lib/jmap/client';
 import type { IJMAPClient } from '@/lib/jmap/client-interface';
 import { useAuthStore } from '@/stores/auth-store';
@@ -10,8 +10,11 @@ import { useSettingsStore } from '@/stores/settings-store';
 import { usePluginStore } from '@/stores/plugin-store';
 import { useThemeStore } from '@/stores/theme-store';
 import { DEFAULT_SEARCH_FILTERS } from '@/lib/jmap/search-utils';
+import { useUIStore } from '@/stores/ui-store';
 import { threadKeyFor } from '@/lib/thread-utils';

+const device = vi.hoisted(() => ({ mobile: false }));
+
 // Keep the real MailApp selection/download handlers and EmailViewer. Stub
 // unrelated shell UI and bootstrap requests so no server is contacted.
 vi.mock('next/dynamic', () => ({ default: (load: () => Promise<React.ComponentType<Record<string, unknown>>>) => {
@@ -25,6 +28,8 @@ vi.mock('@/components/layout/sidebar', () => ({ Sidebar: () => null }));
 vi.mock('@/components/layout/navigation-rail', () => ({ NavigationRail: () => null }));
 vi.mock('@/components/layout/calendar-event-notification-toaster', () => ({ CalendarEventNotificationToaster: () => null }));
 vi.mock('@/components/layout/share-notification-toaster', () => ({ ShareNotificationToaster: () => null }));
+vi.mock('@/components/layout/mv-top-bar', () => ({ MvTopBar: () => null }));
+vi.mock('@/components/layout/mv-side-panel', () => ({ MvSidePanel: () => null }));
 vi.mock('@/components/layout/mobile-header', () => ({ MobileHeader: () => null }));
 vi.mock('@/components/email/message-list-tabs', () => ({ MessageListTabs: () => null }));
 vi.mock('@/components/search/search-box', () => ({ SearchBox: () => null }));
@@ -38,22 +43,38 @@ vi.mock('@/hooks/use-pro-multi-account-mailboxes', () => ({ useProMultiAccountMa
 vi.mock('@/hooks/use-wopi-status', () => ({ useWopiStatus: () => null, canWopiOpen: () => false }));
 vi.mock('@/hooks/use-browser-navigation', () => ({ useBrowserNavigation: () => {} }));
 vi.mock('@/hooks/use-media-query', () => ({
-  useDeviceDetection: () => ({ isMobile: false, isTablet: false, isDesktop: true }),
+  useDeviceDetection: () => ({ isMobile: device.mobile, isTablet: false, isDesktop: !device.mobile }),
  useMediaQuery: () => false,
  useIsDesktop: () => true,
 }));
 vi.mock('@/lib/push-bindings', () => ({ reconcilePushBindings: () => {}, releasePushBindings: () => {} }));
-vi.mock('@/components/email/email-list', () => ({ EmailList: ({ emails, onEmailSelect, onOpenAttachment }: {
-  emails: Email[]; onEmailSelect: (email: Email) => void; onOpenAttachment: (email: Email, attachment: NonNullable<Email['attachments']>[number]) => void;
-}) => <div>{emails.map((email, i) => <div key={i}>
-  <button onClick={() => onEmailSelect(email)}>Select {i}</button>
-  <button onClick={() => onOpenAttachment(email, email.attachments![0])}>List attachment {i}</button>
-</div>)}</div> }));
+vi.mock('@/components/email/email-list', async () => {
+  const { ThreadListItem } = await import('@/components/email/thread-list-item');
+  const { groupEmailsByThread } = await import('@/lib/thread-utils');
+  return { EmailList: ({ emails, onEmailSelect, onOpenAttachment, onOpenConversation }: {
+    emails: Email[];
+    onOpenConversation: (thread: ThreadGroup) => void;
+    onEmailSelect: (email: Email) => void;
+    onOpenAttachment: (email: Email, attachment: NonNullable<Email['attachments']>[number]) => void;
+  }) => device.mobile ? (
+    <div>{groupEmailsByThread(emails).map(thread => (
+      <ThreadListItem key={thread.threadKey} thread={thread} isExpanded={false}
+        onToggleExpand={() => {}} onEmailSelect={onEmailSelect} onOpenConversation={onOpenConversation} />
+    ))}</div>
+  ) : (
+    <div>{emails.map((email, i) => <div key={i}>
+      <button onClick={() => onEmailSelect(email)}>Select {i}</button>
+      <button onClick={() => onOpenAttachment(email, email.attachments![0])}>List attachment {i}</button>
+    </div>)}</div>
+  ) };
+});
 vi.mock('@/components/files/file-preview-modal', () => ({ FilePreviewModal: ({ onDownload, getFileContent }: {
  onDownload: () => void; getFileContent: () => Promise<unknown>;
 }) => <div><button onClick={onDownload}>Preview download</button><button onClick={() => void getFileContent()}>Preview fetch</button></div> }));

 const { MailApp } = await import('../mail-app');
+const { ConversationEmailBody } = await import('@/components/email/thread-conversation-view');
+const { EmailViewer } = await import('@/components/email/email-viewer');

 const sharedMailbox = { id: 'nrichmond:inbox', originalId: 'inbox', name: 'Shared', isShared: true, accountId: 'nrichmond' } as Mailbox;
 const primaryMailbox = { id: 'inbox', name: 'Inbox', role: 'inbox' } as Mailbox;
@@ -90,6 +111,8 @@ let other: ReturnType<typeof makeClient>;
 const asClient = (c: ReturnType<typeof makeClient>) => c as unknown as IJMAPClient;

 beforeEach(() => {
+  device.mobile = false;
+  useUIStore.setState({ isMobile: false });
  vi.stubGlobal('fetch', vi.fn().mockRejectedValue(new Error('Unexpected network request')));
  usePluginStore.setState({ initializePlugins: vi.fn().mockResolvedValue(undefined) });
  useThemeStore.setState({ syncServerThemes: vi.fn().mockResolvedValue(undefined) });
@@ -104,7 +127,7 @@ beforeEach(() => {
    getClientForAccount: (id) => (id === 'login-primary' ? asClient(primary) : id === 'login-other' ? asClient(other) : undefined) as never,
    getAllConnectedClients: () => new Map([['login-primary', asClient(primary)], ['login-other', asClient(other)]]) as never,
  });
-  useSettingsStore.setState({ enableUnifiedMailbox: false, mailAttachmentAction: 'download', mailLayout: 'split', attachmentImagePreviewsEnabled: false, postExportAction: 'none', attachmentDownloadTemplate: '{filename}', filenameLowercase: false } as never);
+  useSettingsStore.setState({ interfaceLayout: 'default', markAsReadDelay: -1, enableUnifiedMailbox: false, mailAttachmentAction: 'download', mailLayout: 'split', attachmentImagePreviewsEnabled: false, postExportAction: 'none', attachmentDownloadTemplate: '{filename}', filenameLowercase: false } as never);
  useEmailStore.setState({
    emails: [message()], selectedEmail: message(), selectedMailbox: sharedMailbox.id,
    mailboxes: [primaryMailbox, sharedMailbox], viewingAccountId: null, accountMailboxes: {},
@@ -352,3 +375,230 @@ describe('standard mail UI blob routing', () => {
    await waitFor(() => expect(primary.fetchBlob).toHaveBeenCalledWith('same-blob', 'inline.png', 'image/png', 'nrichmond'));
  });
 });
+
+
+// Exercise real thread-row clicks, MailApp conversation loading, the card body,
+// and JMAP URL/authentication. Only unrelated shell UI and responses are mocked.
+async function conversationClients() {
+  const a = await connectDownloadClient('https://primary.example.com', 'primary-login', 'postal12345');
+  const b = await connectDownloadClient('https://secondary.example.com', 'secondary-login', 'secondary-primary');
+  useAuthStore.setState({ client: a,
+    getClientForAccount: id => id === 'login-primary' ? a : id === 'login-other' ? b : undefined,
+    getAllConnectedClients: () => new Map([['login-primary', a], ['login-other', b]]),
+  });
+  const fetchMock = vi.mocked(fetch);
+  fetchMock.mockClear();
+  fetchMock.mockImplementation(async () => new Response('blob bytes', {
+    status: 200, headers: { 'Content-Type': 'image/png' },
+  }));
+  vi.spyOn(HTMLAnchorElement.prototype, 'click').mockImplementation(() => {});
+  return { a, b, fetchMock };
+}
+const cardAttachment = { partId: '3', blobId: 'same-blob', name: 'card.png', type: 'image/png', size: 50 };
+function conversationMessage(overrides: Partial<Email> = {}) {
+  return message({ id: 'card', subject: 'Routing conversation', attachments: [cardAttachment], ...overrides });
+}
+function inlineMessage(overrides: Partial<Email> = {}) {
+  return conversationMessage({
+    htmlBody: [{ partId: '1', blobId: 'html-blob', type: 'text/html', size: 30 }], textBody: [],
+    bodyValues: { '1': { value: '<img src="cid:test-image">', isTruncated: false, isEncodingProblem: false } },
+    attachments: [{ ...cardAttachment, cid: 'test-image' }], ...overrides,
+  });
+}
+function expectBlobRequest(url: string, login: string, index = 0) {
+  const calls = vi.mocked(fetch).mock.calls;
+  expect(String(calls[index][0])).toBe(url);
+  expect(calls[index][1]?.headers).toEqual(expect.objectContaining({
+    Authorization: `Basic ${btoa(`${login}:test-password`)}`,
+  }));
+}
+async function openPhoneConversation(ref: Email, threadClient: JMAPClient, selected: Email | null = null, unified = true) {
+  device.mobile = true;
+  useUIStore.setState({ isMobile: true });
+  const older = { ...ref, id: 'older', receivedAt: '2025-12-31T00:00:00Z', attachments: [] };
+  // Email/get/Thread/get results have no UI source stamps.
+  const raw = (email: Email) => ({ ...email, sourceClientAccountId: undefined, sourceAccountId: undefined });
+  const threadFetch = vi.spyOn(threadClient, 'getThreadEmails').mockResolvedValue([raw(ref), raw(older)]);
+  useEmailStore.setState({ emails: [ref, older], selectedEmail: selected,
+    selectedMailbox: unified ? '__unified_inbox__' : sharedMailbox.id,
+    isUnifiedView: unified, unifiedRole: unified ? 'inbox' : null,
+  });
+  render(<MailApp />);
+  fireEvent.click(await screen.findByText('Routing conversation'));
+  await screen.findByRole('button', { name: 'email_viewer.back_to_list' });
+  await waitFor(() => expect(threadFetch).toHaveBeenCalled());
+  await screen.findByText('threads.messages_other');
+  return threadFetch;
+}
+
+describe('conversation blob routing', () => {
+  it.each([
+    { source: 'direct shared folder', login: 'login-primary', owner: 'nrichmond', unified: false },
+    { source: 'secondary login and shared owner', login: 'login-other', owner: 'nrichmond', unified: true },
+    { source: 'primary account', login: 'login-primary', owner: 'postal12345', unified: true },
+  ])('routes phone CID images for $source', async ({ login, owner, unified }) => {
+    const { a, b, fetchMock } = await conversationClients();
+    const ref = inlineMessage(unified ? { sourceClientAccountId: login, sourceAccountId: owner } : {});
+    const threadFetch = await openPhoneConversation(ref, login === 'login-other' ? b : a, null, unified);
+    expect(threadFetch).toHaveBeenCalledWith('thread', unified ? owner : 'nrichmond');
+    await waitFor(() => expect(fetchMock).toHaveBeenCalledTimes(1));
+    expectBlobRequest(`https://${login === 'login-other' ? 'secondary' : 'primary'}.example.com/download/${owner}/same-blob/card.png?accept=image%2Fpng`, login === 'login-other' ? 'secondary-login' : 'primary-login');
+  });
+
+  it('routes a direct shared-folder conversation through the browsing login', async () => {
+    const { b, fetchMock } = await conversationClients();
+    useEmailStore.setState({ viewingAccountId: 'login-other', accountMailboxes: { 'login-other': [sharedMailbox] } });
+    await openPhoneConversation(inlineMessage(), b, null, false);
+    await waitFor(() => expect(fetchMock).toHaveBeenCalledTimes(1));
+    expectBlobRequest('https://secondary.example.com/download/nrichmond/same-blob/card.png?accept=image%2Fpng', 'secondary-login');
+  });
+
+  it.each([
+    { selection: 'null', login: 'login-other', owner: 'nrichmond' },
+    { selection: 'unrelated', login: 'login-other', owner: 'nrichmond' },
+    { selection: 'null', login: 'login-primary', owner: 'postal12345' },
+  ])('downloads the phone card on $login with $selection selectedEmail', async ({ selection, login, owner }) => {
+    const { a, b, fetchMock } = await conversationClients();
+    const selected = selection === 'null' ? null : message({ id: 'unrelated', subject: 'Other message', sourceClientAccountId: 'login-primary', sourceAccountId: 'unrelated-owner' });
+    await openPhoneConversation(conversationMessage({ sourceClientAccountId: login, sourceAccountId: owner }), login === 'login-other' ? b : a, selected);
+    fireEvent.click(await screen.findByRole('button', { name: /card.png/ }));
+    await waitFor(() => expect(fetchMock).toHaveBeenCalledTimes(1));
+    expectBlobRequest(`https://${login === 'login-other' ? 'secondary' : 'primary'}.example.com/download/${owner}/same-blob/card.png?accept=image%2Fpng`, login === 'login-other' ? 'secondary-login' : 'primary-login');
+  });
+
+  it.each([false, true])('retains phone preview routing after navigation (direct shared=%s)', async direct => {
+    const { a, b, fetchMock } = await conversationClients();
+    useSettingsStore.setState({ mailAttachmentAction: 'preview' });
+    const ref = conversationMessage(direct ? {} : { sourceClientAccountId: 'login-other', sourceAccountId: 'nrichmond' });
+    await openPhoneConversation(ref, direct ? a : b, null, !direct);
+    fireEvent.click(await screen.findByRole('button', { name: /card.png/ }));
+    await screen.findByText('Preview fetch');
+    act(() => {
+      useEmailStore.setState({ selectedMailbox: 'inbox', selectedEmail: message({ sourceClientAccountId: 'login-primary', sourceAccountId: 'other-owner' }) });
+      useAuthStore.setState({ client: b, activeAccountId: 'login-other' });
+    });
+    fireEvent.click(screen.getByText('Preview fetch'));
+    fireEvent.click(screen.getByText('Preview download'));
+    await waitFor(() => expect(fetchMock).toHaveBeenCalledTimes(2));
+    for (const index of [0, 1]) expectBlobRequest(`https://${direct ? 'primary' : 'secondary'}.example.com/download/nrichmond/same-blob/card.png?accept=image%2Fpng`, direct ? 'primary-login' : 'secondary-login', index);
+  });
+
+  it.each([false, true])('routes Mountain View expanded sibling CID and attachment (mobile=%s)', async mobile => {
+    const { b, fetchMock } = await conversationClients();
+    device.mobile = mobile;
+    useUIStore.setState({ isMobile: mobile });
+    useSettingsStore.setState({ interfaceLayout: 'mountain-view' });
+    const sibling = inlineMessage({ attachments: [...inlineMessage().attachments!, { ...cardAttachment, name: 'download.png', partId: '4' }], id: 'sibling', from: [{ name: 'Older sender', email: 'older@example.com' }], sourceClientAccountId: 'login-other', sourceAccountId: 'nrichmond' });
+    const open = conversationMessage({ id: 'open', attachments: [], receivedAt: '2026-01-02T00:00:00Z', sourceClientAccountId: 'login-other', sourceAccountId: 'nrichmond' });
+    const download = vi.fn();
+    const { container } = render(<EmailViewer email={open} blobSource={{ client: b, accountId: 'nrichmond' }} mvConversation={[sibling, open]} onDownloadAttachment={download} />);
+    fireEvent.click(await screen.findByText('Older sender'));
+    await waitFor(() => expect(fetchMock).toHaveBeenCalledTimes(1));
+    expectBlobRequest('https://secondary.example.com/download/nrichmond/same-blob/card.png?accept=image%2Fpng', 'secondary-login');
+    const card = container.querySelector('[data-mv-conversation-expanded]') as HTMLElement;
+    fireEvent.click(within(card).getByRole('button', { name: /download.png/ }));
+    expect(download).toHaveBeenCalledWith('same-blob', 'download.png', 'image/png', false, expect.objectContaining({ client: b, accountId: 'nrichmond' }));
+  });
+
+  it('downloads overlapping card blob ids from successive phone conversations', async () => {
+    const { a, b, fetchMock } = await conversationClients();
+    device.mobile = true;
+    useUIStore.setState({ isMobile: true });
+    const one = conversationMessage({ subject: 'First conversation', sourceClientAccountId: 'login-primary', sourceAccountId: 'owner-a' });
+    const two = conversationMessage({ subject: 'Second conversation', sourceClientAccountId: 'login-other', sourceAccountId: 'owner-b' });
+    const rows = [one, { ...one, id: 'older' }, two, { ...two, id: 'older' }];
+    vi.spyOn(a, 'getThreadEmails').mockResolvedValue([one]);
+    vi.spyOn(b, 'getThreadEmails').mockResolvedValue([two]);
+    useEmailStore.setState({ emails: rows, selectedEmail: null, selectedMailbox: '__unified_inbox__', isUnifiedView: true, unifiedRole: 'inbox' });
+    render(<MailApp />);
+    fireEvent.click(await screen.findByText('First conversation'));
+    fireEvent.click(await screen.findByRole('button', { name: /card.png/ }));
+    await waitFor(() => expect(fetchMock).toHaveBeenCalledTimes(1));
+    fireEvent.click(screen.getByRole('button', { name: 'email_viewer.back_to_list' }));
+    fireEvent.click(screen.getByText('Second conversation'));
+    fireEvent.click(await screen.findByRole('button', { name: /card.png/ }));
+    await waitFor(() => expect(fetchMock).toHaveBeenCalledTimes(2));
+    expectBlobRequest('https://primary.example.com/download/owner-a/same-blob/card.png?accept=image%2Fpng', 'primary-login', 0);
+    expectBlobRequest('https://secondary.example.com/download/owner-b/same-blob/card.png?accept=image%2Fpng', 'secondary-login', 1);
+  });
+
+  it.each(['owner', 'client'] as const)('scopes Mountain View pending loads when only the %s changes', async changed => {
+    const { a, b, fetchMock } = await conversationClients();
+    useSettingsStore.setState({ interfaceLayout: 'mountain-view' });
+    const nextOwner = changed === 'owner' ? 'next-owner' : 'nrichmond';
+    const nextMailbox = { ...sharedMailbox, id: 'next-inbox', accountId: nextOwner };
+    const open = conversationMessage({ id: 'open', attachments: [], receivedAt: '2026-01-02T00:00:00Z' });
+    const sibling = (label: string) => conversationMessage({
+      id: 'sibling', keywords: {}, from: [{ name: label, email: 'older@example.com' }],
+    });
+    const getThreadA = vi.spyOn(a, 'getThread').mockResolvedValue({ id: 'thread', emailIds: ['sibling', 'open'] });
+    const getThreadB = vi.spyOn(b, 'getThread').mockResolvedValue({ id: 'thread', emailIds: ['sibling', 'open'] });
+    vi.spyOn(a, 'getSomeEmails').mockImplementation(async (_ids, owner) => [sibling(owner === nextOwner && changed === 'owner' ? 'Next sender' : 'First sender'), { ...open }]);
+    vi.spyOn(b, 'getSomeEmails').mockResolvedValue([sibling('Next sender'), { ...open }]);
+    useEmailStore.setState({ emails: [open], selectedEmail: open, selectedMailbox: sharedMailbox.id,
+      mailboxes: [sharedMailbox, nextMailbox], accountMailboxes: { 'login-other': [sharedMailbox, nextMailbox] },
+    });
+    const { container } = render(<MailApp />);
+    await screen.findByText('First sender');
+    expect(fetchMock).not.toHaveBeenCalled();
+    act(() => useEmailStore.setState({
+      selectedMailbox: nextMailbox.id, selectedEmail: { ...open },
+      viewingAccountId: changed === 'client' ? 'login-other' : null,
+    }));
+    await waitFor(() => expect(container.querySelector('[data-mv-conversation-expanded]')?.textContent).toContain('Next sender'));
+    const card = container.querySelector('[data-mv-conversation-expanded]') as HTMLElement;
+    fireEvent.click(within(card).getByRole('button', { name: /card.png/ }));
+    await waitFor(() => expect(fetchMock).toHaveBeenCalledTimes(1));
+    expect(changed === 'client' ? getThreadB : getThreadA).toHaveBeenLastCalledWith('thread', nextOwner);
+    expectBlobRequest(`https://${changed === 'client' ? 'secondary' : 'primary'}.example.com/download/${nextOwner}/same-blob/card.png?accept=image%2Fpng`, changed === 'client' ? 'secondary-login' : 'primary-login');
+  });
+
+  it('does not fetch a disconnected stamped source through another login', async () => {
+    const { fetchMock } = await conversationClients();
+    render(<ConversationEmailBody email={inlineMessage({ sourceClientAccountId: 'disconnected', sourceAccountId: 'nrichmond' })} allowExternal={false} onAllowExternal={() => {}} />);
+    await act(async () => {});
+    expect(fetchMock).not.toHaveBeenCalled();
+  });
+
+  it('isolates equal email/blob/CID ids across clients and owners and discards late CID results', async () => {
+    await conversationClients();
+    let finishFirst!: (blob: Blob) => void;
+    const firstClient = asClient(primary);
+    const secondClient = asClient(other);
+    const first = vi.spyOn(firstClient, 'fetchBlob').mockImplementation(() => new Promise(resolve => { finishFirst = resolve; }));
+    const second = vi.spyOn(secondClient, 'fetchBlob').mockResolvedValue(new Blob(['second'], { type: 'image/png' }));
+    useAuthStore.setState({ client: firstClient as never,
+      getClientForAccount: id => (id === 'login-primary' ? firstClient : secondClient) as never,
+    });
+    const attachments = inlineMessage().attachments;
+    const one = inlineMessage({ attachments, sourceClientAccountId: 'login-primary', sourceAccountId: 'owner-a' });
+    const two = { ...one, sourceClientAccountId: 'login-other', sourceAccountId: 'owner-b' };
+    vi.mocked(URL.createObjectURL).mockReturnValueOnce('blob:second').mockReturnValueOnce('blob:late');
+    const body = (email: Email) => <ConversationEmailBody email={email} allowExternal={false} onAllowExternal={() => {}} />;
+    const { container, rerender, unmount } = render(body(one));
+    await waitFor(() => expect(first).toHaveBeenCalled());
+    rerender(body(two));
+    await waitFor(() => expect(second).toHaveBeenCalledWith('same-blob', 'card.png', 'image/png', 'owner-b'));
+    await waitFor(() => expect(container.querySelector('iframe')?.getAttribute('srcdoc')).toContain('blob:second'));
+    await act(async () => finishFirst(new Blob(['late'], { type: 'image/png' })));
+    expect(container.querySelector('iframe')?.getAttribute('srcdoc')).toContain('blob:second');
+    expect(URL.revokeObjectURL).toHaveBeenCalledWith('blob:late');
+    unmount();
+    expect(URL.revokeObjectURL).toHaveBeenCalledWith('blob:second');
+  });
+
+  it('clears resolved CID URLs immediately when only the owning account changes', async () => {
+    const { a, fetchMock } = await conversationClients();
+    vi.mocked(URL.createObjectURL).mockReturnValue('blob:owner-a');
+    const first = inlineMessage({ sourceClientAccountId: 'login-primary', sourceAccountId: 'owner-a' });
+    const body = (email: Email) => <ConversationEmailBody email={email} allowExternal={false} onAllowExternal={() => {}} />;
+    const { container, rerender } = render(body(first));
+    await waitFor(() => expect(container.querySelector('iframe')?.getAttribute('srcdoc')).toContain('blob:owner-a'));
+    vi.spyOn(a, 'fetchBlob').mockImplementation(() => new Promise(() => {}));
+    rerender(body({ ...first, sourceAccountId: 'owner-b' }));
+    expect(container.querySelector('iframe')?.getAttribute('srcdoc')).not.toContain('blob:owner-a');
+    expect(fetchMock).toHaveBeenCalledTimes(1);
+    expect(a.fetchBlob).toHaveBeenLastCalledWith('same-blob', 'card.png', 'image/png', 'owner-b');
+    expect(URL.revokeObjectURL).toHaveBeenCalledWith('blob:owner-a');
+  });
+});
@@ -35,7 +35,7 @@ import type { UnifiedAccountClient } from "@/lib/unified-mailbox";
 import { connectedAccountsGrew } from "@/lib/unified-mailbox";
 import { messagePriorityFromHeaders, type MessagePriority } from "@/lib/message-priority";
 import { KeyboardShortcutsModal } from "@/components/keyboard-shortcuts-modal";
-import { useEmailStore, pendingInitialData, buildUnifiedAccountClients, invalidateUnifiedMailboxes, captureViewToken, ArchiveMailboxNotFoundError, ensureArchiveMailbox, resolveSelectedEmails, resolveUnstampedEmailAccountId, resolveEmailBlobContext, emptyFolderMovesToTrash, bulkDeleteIsPermanent, shouldConfirmBulkDelete, removalFolder, canRemoveFromFolder } from "@/stores/email-store";
+import { useEmailStore, pendingInitialData, buildUnifiedAccountClients, invalidateUnifiedMailboxes, captureViewToken, ArchiveMailboxNotFoundError, ensureArchiveMailbox, resolveSelectedEmails, resolveUnstampedEmailAccountId, resolveEmailBlobContext, type EmailBlobContext, emptyFolderMovesToTrash, bulkDeleteIsPermanent, shouldConfirmBulkDelete, removalFolder, canRemoveFromFolder } from "@/stores/email-store";
 import { useRemoveFromFolder } from "@/hooks/use-remove-from-folder";
 import { groupSearchScopeFolders, SEARCH_SCOPE_ALL_FOLDERS } from "@/lib/search-scope-folders";
 import { toast } from "@/stores/toast-store";
@@ -233,6 +233,8 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
  const [isResizing, setIsResizing] = useState(false);
  const dragStartWidth = useRef(0);
  // Mobile conversation view state
+  const [conversationBlobSource, setConversationBlobSource] = useState<EmailBlobContext | undefined>();
+  const conversationOpenSeqRef = useRef(0);
  const [conversationThread, setConversationThread] = useState<ThreadGroup | null>(null);
  // Mountain View writes replies in place under the conversation until the
  // user pops one out into the docked window.
@@ -242,11 +244,17 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
  }, [showComposer]);
  const handleMvPopOut = useCallback(() => setMvReplyPoppedOut(true), []);
  // Mountain View: the open message's whole conversation, light properties only.
-  const [mvConversation, setMvConversation] = useState<Email[] | null>(null);
+  const [mvConversationResult, setMvConversationResult] = useState<{
+    emails: Email[]; source: EmailBlobContext; threadId: string;
+  } | null>(null);
  // The thread whose conversation is being fetched, so the viewer waits for it
  // instead of showing the message alone first. (#1223)
  const [mvConversationLoading, setMvConversationLoading] = useState<string | null>(null);
-  const mvConversationLoadRef = useRef<{ key: string; startedAt: number; promise: Promise<Email[] | null> } | null>(null);
+  const mvConversationLoadRef = useRef<{
+    client: NonNullable<EmailBlobContext['client']>; accountId?: string;
+    threadId: string; emailId: string; startedAt: number; promise: Promise<Email[] | null>;
+  } | null>(null);
+  const mvConversationOpenSeqRef = useRef(0);
  const [conversationEmails, setConversationEmails] = useState<Email[]>([]);
  const [isLoadingConversation, setIsLoadingConversation] = useState(false);
  const [rateLimitSecondsLeft, setRateLimitSecondsLeft] = useState<number | null>(null);
@@ -768,6 +776,8 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
    // to return to a thread, we silently skip - back navigation always works.
    if ((state.threadId ?? null) !== ctx.conversationThreadId) {
      if (state.threadId === null) {
+        ++conversationOpenSeqRef.current;
+        setConversationBlobSource(undefined);
        setConversationThread(null);
        setConversationEmails([]);
      }
@@ -1784,9 +1794,14 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
    // Conversation. One fetch serves both layouts: mobile opens the dedicated
    // conversation view, desktop opens the newest message of the thread (which
    // is what clicking a thread in the list does there).
+    const openSeq = ++conversationOpenSeqRef.current;
+    const source: EmailBlobContext = {
+      client: activeClient, clientAccountId: useAuthStore.getState().activeAccountId ?? undefined,
+    };
    setLoadingEmail(true);
    try {
      const threadEmails = await activeClient.getThreadEmails(link.id);
+      if (openSeq !== conversationOpenSeqRef.current) return;
      const [group] = groupEmailsByThread(threadEmails);
      if (!group) {
        toast.error(t('deep_link.thread_not_found'));
@@ -1794,6 +1809,7 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
      }
      if (isMobile) {
        setConversationThread(group);
+        setConversationBlobSource(source);
        setConversationEmails(threadEmails);
        setActiveView('viewer');
      } else {
@@ -2833,6 +2849,8 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
      if (!archived) return;

      if (conversationThread && conversationThread.threadKey === threadKeyFor(emailToArchive)) {
+        ++conversationOpenSeqRef.current;
+        setConversationBlobSource(undefined);
        setConversationThread(null);
        setConversationEmails([]);
      }
@@ -3685,8 +3703,8 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
    return load;
  }, []);

-  const handleDownloadAttachment = async (blobId: string, name: string, type?: string, forceDownload?: boolean) => {
-    const { blobClient, accountId, clientAccountId } = resolveBlobSource(selectedEmail);
+  const handleDownloadAttachment = async (blobId: string, name: string, type?: string, forceDownload?: boolean, source?: EmailBlobContext) => {
+    const { client: blobClient, accountId, clientAccountId } = source ?? resolveEmailBlobContext(selectedEmail, client);
    if (!blobClient) return;

    try {
@@ -3706,6 +3724,9 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
    }
  };

+  const handleDownloadConversationAttachment = (blobId: string, name: string, type: string | undefined, source: EmailBlobContext) =>
+    handleDownloadAttachment(blobId, name, type, false, source);
+
  const handlePreviewAttachmentDownload = useCallback(async () => {
    const c = previewAttachment?.client;
    if (!c || !previewAttachment) return;
@@ -3890,26 +3911,31 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
  const mvConversationThreadId = mvConversationView && !cursorOnly ? (selectedEmail?.threadId ?? null) : null;
  const mvConversationRef = mvConversationView && !cursorOnly ? selectedEmail : null;
  const mvConversationRoute = (ref: Email, fallback: NonNullable<typeof client>) => {
-    const route = resolveThreadRoute({ isUnifiedView, ref, mailboxes: viewMailboxes, selectedMailbox });
-    const threadClient = route.clientAccountId
-      ? (useAuthStore.getState().getClientForAccount(route.clientAccountId) ?? fallback)
-      : fallback;
-    return { threadClient, accountId: route.accountId };
+    const source = resolveEmailBlobContext(ref, fallback);
+    return { threadClient: source.client, accountId: source.accountId };
  };
+  const mvBlobSource = resolveEmailBlobContext(mvConversationRef, client);
+  // Do not render the previous owner's cards while the replacement loads.
+  const mvConversation = mvConversationResult?.source.client === mvBlobSource.client
+    && mvConversationResult?.source.accountId === mvBlobSource.accountId
+    && mvConversationResult?.threadId === mvConversationThreadId
+    ? mvConversationResult.emails : null;
  // Fetches the conversation around `ref`, oldest first. Opening a message
  // starts this next to the message fetch, and the effect below picks up that
  // same request rather than sending a second one.
  const loadMvConversation = (ref: Email, fallback: NonNullable<typeof client>): Promise<Email[] | null> => {
-    const key = `${ref.sourceClientAccountId ?? ''}:${ref.sourceAccountId ?? ''}:${ref.threadId}:${ref.id}`;
+    const { threadClient, accountId } = mvConversationRoute(ref, fallback);
+    if (!threadClient) return Promise.resolve(null);
    const pending = mvConversationLoadRef.current;
-    if (pending?.key === key && Date.now() - pending.startedAt < 10_000) return pending.promise;
-    const route = mvConversationRoute(ref, fallback);
-    const threadClient = route.threadClient;
+    // Bare ids overlap across shared owners and across connected clients.
+    if (pending?.client === threadClient && pending.accountId === accountId
+      && pending.threadId === ref.threadId && pending.emailId === ref.id
+      && Date.now() - pending.startedAt < 10_000) return pending.promise;
    const promise = (async () => {
-      const thread = await threadClient.getThread(ref.threadId, route.accountId);
+      const thread = await threadClient.getThread(ref.threadId, accountId);
      const ids = thread?.emailIds ?? [];
      if (ids.length < 2) return null;
-      const emails = await threadClient.getSomeEmails(ids, route.accountId);
+      const emails = await threadClient.getSomeEmails(ids, accountId);
      for (const e of emails) {
        // Carry the open message's source stamps, so opening one of these
        // in a merged view reaches the right account.
@@ -3922,37 +3948,45 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
        .filter((e) => e.id === ref.id || !e.keywords?.$draft)
        .sort((a, b) => a.receivedAt.localeCompare(b.receivedAt));
    })().catch(() => null);
-    mvConversationLoadRef.current = { key, startedAt: Date.now(), promise };
+    mvConversationLoadRef.current = { client: threadClient, accountId, threadId: ref.threadId, emailId: ref.id, startedAt: Date.now(), promise };
    return promise;
  };

  useEffect(() => {
+    ++mvConversationOpenSeqRef.current;
    if (!mvConversationThreadId || !client || !mvConversationRef) {
-      setMvConversation(null);
+      setMvConversationResult(null);
      setMvConversationLoading(null);
      return;
    }
    let cancelled = false;
+    setMvConversationResult(null);
    setMvConversationLoading(mvConversationThreadId);
    void loadMvConversation(mvConversationRef, client).then((conversation) => {
      if (cancelled) return;
-      setMvConversation(conversation);
+      setMvConversationResult(conversation ? {
+        emails: conversation, source: mvBlobSource, threadId: mvConversationThreadId,
+      } : null);
      setMvConversationLoading(null);
    });
-    return () => { cancelled = true; };
+    return () => { cancelled = true; ++mvConversationOpenSeqRef.current; };
    // eslint-disable-next-line react-hooks/exhaustive-deps -- keyed on the open message, not on every list refresh
-  }, [mvConversationThreadId, mvConversationRef?.id, client]);
+  }, [mvConversationThreadId, mvConversationRef?.id, mvBlobSource.client, mvBlobSource.accountId, client]);

  const patchMvConversation = (id: string, patch: (e: Email) => Email) =>
-    setMvConversation((prev) => prev?.map((e) => (e.id === id ? patch(e) : e)) ?? prev);
+    setMvConversationResult(prev => prev ? {
+      ...prev, emails: prev.emails.map(e => e.id === id ? patch(e) : e),
+    } : null);

  // An unfolded conversation message needs its body: the thread fetch above
  // only carries list properties.
  const handleLoadConversationEmail = async (target: Email): Promise<Email | null> => {
    if (!client) return null;
    const { threadClient, accountId } = mvConversationRoute(target, client);
+    if (!threadClient) return null;
+    const openSeq = mvConversationOpenSeqRef.current;
    const fetched = await threadClient.getEmail(target.id, accountId);
-    if (!fetched) return null;
+    if (!fetched || openSeq !== mvConversationOpenSeqRef.current) return null;
    const full: Email = {
      ...fetched,
      accountId: target.accountId,
@@ -3982,6 +4016,7 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
          return;
        }
        const { threadClient, accountId } = mvConversationRoute(target, client);
+        if (!threadClient) return;
        await threadClient.markAsRead(target.id, true, accountId);
        void emailHooks.onEmailReadStateChange.emit({ emailIds: [target.id], read: true });
      }
@@ -4138,7 +4173,8 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {

    // Fetch the full content
    try {
-      const { client: fetchClient, accountId } = resolveEmailBlobContext(listEmail ?? null, client);
+      const source = resolveEmailBlobContext(listEmail ?? null, client);
+      const { client: fetchClient, accountId } = source;
      if (!fetchClient) {
        console.warn('[mail-app] No connected client for email source');
        if (openSeq === emailOpenSeqRef.current) abandonOpenEmail(previousEmail);
@@ -4180,8 +4216,10 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
            conversationPrefetch,
            new Promise<undefined>((resolve) => setTimeout(() => resolve(undefined), MV_CONVERSATION_WAIT_MS)),
          ]);
-          if (conversation !== undefined) setMvConversation(conversation);
          if (openSeq !== emailOpenSeqRef.current) return;
+          if (conversation !== undefined) setMvConversationResult(conversation ? {
+            emails: conversation, source, threadId: fullEmail.threadId,
+          } : null);
        }
        // One write: the message, and the end of its loading state.
        finishOpenEmail(fullEmail);
@@ -4202,6 +4240,8 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
  // The OS / hardware back button is still wired through popstate → handleNavRestore.
  const handleMobileBack = () => {
    if (conversationThread) {
+      ++conversationOpenSeqRef.current;
+      setConversationBlobSource(undefined);
      setConversationThread(null);
      setConversationEmails([]);
    }
@@ -4226,42 +4266,36 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
  // Handle opening conversation view on mobile
  const handleOpenConversation = async (thread: ThreadGroup) => {
    if (!client) return;
+    const source = resolveEmailBlobContext(thread.latestEmail, client);
+    // Never fetch a stamped thread through an unrelated login.
+    if (!source.client) return;
+    const openSeq = ++conversationOpenSeqRef.current;

-    // The view marks the thread read; keep its row where it was tapped.
    useEmailStore.getState().holdListRow(thread.threadKey);
    setConversationThread(thread);
+    setConversationBlobSource(source);
+    setConversationEmails([]);
    setIsLoadingConversation(true);
    setActiveView("viewer");

    try {
-      // The thread may belong to another account: in unified/aggregate views via
-      // the email's own source stamp (#281), and in a directly-browsed shared
-      // folder via the selected mailbox's owner (#814). Either way the fetch has
-      // to name that account - thread ids are per-account, so an unscoped fetch
-      // resolves to an unrelated thread in the active one.
-      const ref = thread.emails?.[0];
-      const route = resolveThreadRoute({ isUnifiedView, ref, mailboxes: viewMailboxes, selectedMailbox });
-      const threadClient = route.clientAccountId
-        ? (useAuthStore.getState().getClientForAccount(route.clientAccountId) ?? client)
-        : client;
-      const emails = await threadClient.getThreadEmails(thread.threadId, route.accountId);
-      // Re-stamp the source reference so conversation actions (reply/move/…)
-      // resolve to the right account; the fetched objects don't carry it.
-      if (isUnifiedView && ref) {
-        for (const e of emails) {
-          e.accountId = ref.accountId;
-          e.accountLabel = ref.accountLabel;
-          e.sourceClientAccountId = ref.sourceClientAccountId;
-          e.sourceAccountId = ref.sourceAccountId;
-        }
-      }
-      setConversationEmails(emails);
+      const emails = await source.client.getThreadEmails(thread.threadId, source.accountId);
+      if (openSeq !== conversationOpenSeqRef.current) return;
+      // Preserve UI identity stamps; direct-folder messages stay unstamped.
+      const ref = thread.latestEmail;
+      setConversationEmails(emails.map(e => ({
+        ...e,
+        accountId: ref.accountId,
+        accountLabel: ref.accountLabel,
+        sourceClientAccountId: ref.sourceClientAccountId,
+        sourceAccountId: ref.sourceAccountId,
+      })));
    } catch (error) {
+      if (openSeq !== conversationOpenSeqRef.current) return;
      console.error('Failed to fetch thread emails:', error);
-      // Fall back to thread.emails
      setConversationEmails(thread.emails);
    } finally {
-      setIsLoadingConversation(false);
+      if (openSeq === conversationOpenSeqRef.current) setIsLoadingConversation(false);
    }
  };

@@ -5209,7 +5243,8 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
                onReply={handleConversationReply}
                onReplyAll={handleConversationReplyAll}
                onForward={handleConversationForward}
-                onDownloadAttachment={handleDownloadAttachment}
+                blobSource={conversationBlobSource}
+                onDownloadAttachment={handleDownloadConversationAttachment}
                onMarkAsRead={async (emailId, read) => {
                  if (client) {
                    const target = conversationEmails.find((e) => e.id === emailId);
@@ -1043,10 +1043,16 @@ function findListRow(rows: ListRow[], key: string): number {
  return own !== -1 ? own : rows.findIndex((row) => row.members.includes(key));
 }

+export interface EmailBlobContext {
+  client: IJMAPClient | null;
+  accountId?: string;
+  clientAccountId?: string;
+}
+
 export function resolveEmailBlobContext(
  email: Pick<Email, 'sourceClientAccountId' | 'sourceAccountId'> | null,
  passedClient: IJMAPClient | null,
-): { client: IJMAPClient | null; accountId?: string; clientAccountId?: string } {
+): EmailBlobContext {
  const state = useEmailStore.getState();
  const auth = useAuthStore.getState();
  const clientAccountId = email?.sourceClientAccountId ?? state.viewingAccountId ?? undefined;