fix: keep the reader still while the list changes, and give Pro tabs no list ticks

components/email/__tests__/viewer-list-selection-prop.test.tsx

@@ -63,4 +63,24 @@ describe('the reader panel prop listSelection', () => {
     act(() => { useEmailStore.setState({ emails: [row('new'), row('a'), row('b'), row('c')] }); });
     expect(seen.at(-1)?.listSelection).toBe(before);
   });
+
+  it('does not render the reader again when the list changes but the ticks do not', () => {
+    useAuthStore.setState({ client });
+    useEmailStore.setState({ emails: [row('a'), row('b')], selectedEmailKeys: new Set(['a', 'b']), selectedMailbox: 'inbox', mailboxes });
+    render(<EmailViewer email={null} isLoading={false} mailboxes={mailboxes} selectedMailbox="inbox" currentMailboxRole="inbox" onDelete={() => {}} />);
+    const renders = seen.length;
+    act(() => { useEmailStore.setState({ emails: [row('new'), row('a'), row('b')] }); });
+    act(() => { useEmailStore.setState({ emails: [row('newer'), row('new'), row('a'), row('b')], threadEmailsCache: new Map() }); });
+    expect(seen.length).toBe(renders);
+    // A new tick does.
+    act(() => { useEmailStore.setState({ selectedEmailKeys: new Set(['a', 'b', 'new']) }); });
+    expect(seen.length).toBeGreaterThan(renders);
+  });
+
+  it('gives a panel outside the main list (a Pro tab) no ticks', () => {
+    useAuthStore.setState({ client });
+    useEmailStore.setState({ emails: [row('a'), row('b')], selectedEmailKeys: new Set(['a', 'b']), selectedMailbox: 'inbox', mailboxes });
+    render(<EmailViewer email={null} isLoading={false} mailboxes={mailboxes} selectedMailbox="inbox" currentMailboxRole="inbox" onDelete={() => {}} withListSelection={false} />);
+    expect(seen.at(-1)).toMatchObject({ listSelection: null });
+  });
 });

components/email/email-viewer.tsx

@@ -288,6 +288,8 @@ interface EmailViewerProps {
   mailboxes?: Mailbox[];
   selectedMailbox?: string;
   className?: string;
+  /** The side panel hears of the messages ticked in the main list (false: a Pro tab, whose message isn't from that list). */
+  withListSelection?: boolean;
 }
 
 // Helper function to format recipients with contextual display
@@ -1313,6 +1315,7 @@ export function EmailViewer({
   mailboxes = [],
   selectedMailbox = "",
   className,
+  withListSelection = true,
 }: EmailViewerProps) {
   const t = useTranslations('email_viewer');
   const archiveActionEnabled = useArchiveActionEnabled();
@@ -1819,7 +1822,7 @@ export function EmailViewer({
   }, []);
   const [detailFocusRequest, setDetailFocusRequest] = useState(0);
   // The messages ticked in the list, for the AI assistant (lib/plugin-sandbox/assistant).
-  const listSelection = useListSelection();
+  const listSelection = useListSelection(withListSelection);
   const pluginDetailProps = useMemo(
     () => ({ email: pluginEmailView, selection: bodySelection, listSelection, focusRequest: detailFocusRequest }),
     [pluginEmailView, bodySelection, listSelection, detailFocusRequest],

components/pro/__tests__/pro-email-edit-draft.test.tsx

@@ -143,6 +143,12 @@ describe('Pro email view - editing a draft', () => {
     expect(initialData.draftAccountId).toBeUndefined();
   });
 
+  // The ticks in the main list are another view's: the tab's side panel doesn't get them.
+  it('gives the side panel of an email tab no list selection', async () => {
+    await openAndEdit(undefined);
+    expect(viewerProps.current?.withListSelection).toBe(false);
+  });
+
   // Pro shell with the 0.16.23 login active and the 1.0 login's Drafts
   // browsed: the store reads a row of that list through the 1.0 login. A
   // view that names no login can't tell, so it names none - the active one

components/pro/pro-email-tab-body.tsx

@@ -541,6 +541,7 @@ export function ProEmailView({ emailId, client: clientOverride, clientAccountId,
           currentMailboxRole={currentMailboxRole}
           mailboxes={mailboxes}
           className="flex-1"
+          withListSelection={false}
         />
       </ErrorBoundary>
       <ConfirmDialog {...confirmDialogProps} />

lib/plugin-sandbox/assistant/b.list-selection.ts

@@ -2,7 +2,7 @@
 // the reader panel's `listSelection` prop, so the assistant can work on
 // several at once ("summarise these").
 
-import { useMemo, useRef } from 'react';
+import { useMemo } from 'react';
 import type { IJMAPClient } from '@/lib/jmap/client-interface';
 import { resolveEmailBlobContext, resolveSelectedEmails, useEmailStore } from '@/stores/email-store';
 import { useAuthStore } from '@/stores/auth-store';
@@ -33,18 +33,15 @@ export function listSelectionOf(state: SelectionState, client: IJMAPClient | nul
   return { emails, total };
 }
 
-/** listSelectionOf for the list on screen; the same object while the selection stays the same. */
-export function useListSelection(): ListSelectionView | null {
-  const selectedEmailKeys = useEmailStore((s) => s.selectedEmailKeys);
-  const emails = useEmailStore((s) => s.emails);
-  const threadEmailsCache = useEmailStore((s) => s.threadEmailsCache);
+/**
+ * listSelectionOf for the list on screen; the same object while the
+ * selection stays the same. The store is read through one selector that
+ * answers a string, so new mail, a search or a moved message re-render the
+ * caller only when the ticked messages change. `enabled` false (a Pro tab,
+ * whose panel isn't about the main list) always answers null.
+ */
+export function useListSelection(enabled = true): ListSelectionView | null {
   const client = useAuthStore((s) => s.client);
-  const last = useRef<{ key: string; value: ListSelectionView | null }>({ key: 'null', value: null });
-  return useMemo(() => {
-    const value = listSelectionOf({ selectedEmailKeys, emails, threadEmailsCache }, client);
-    const key = JSON.stringify(value);
-    // New mail arriving re-renders the list; the panel only hears of a new selection.
-    if (key !== last.current.key) last.current = { key, value };
-    return last.current.value;
-  }, [selectedEmailKeys, emails, threadEmailsCache, client]);
+  const key = useEmailStore((s) => (enabled ? JSON.stringify(listSelectionOf(s, client)) : 'null'));
+  return useMemo(() => JSON.parse(key) as ListSelectionView | null, [key]);
 }