feat(list): click sender avatar to select message/thread (Thunderbird-style)

Wrap the message-list avatar in a SelectableAvatar control: clicking the
avatar toggles the row into the current selection instead of opening it,
matching Thunderbird's correspondent-avatar selection affordance. A check
overlay appears on hover (hinting it is clickable) and stays while selected.

- email-list-item + thread single-email: toggle that message's id
- thread header: toggle the whole thread (reuses existing thread-select logic)
- focused-mail and extra-compact layouts render no avatar, so unaffected

components/email/__tests__/selectable-avatar.test.tsx

@@ -0,0 +1,39 @@
+import { describe, it, expect, vi } from 'vitest';
+import { render, screen, fireEvent } from '@testing-library/react';
+import { SelectableAvatar } from '../selectable-avatar';
+
+// Isolate from the real Avatar (image fetching, libravatar hashing) — we only
+// care about the selection wrapper behaviour here.
+vi.mock('@/components/ui/avatar', () => ({
+  Avatar: (props: { name?: string }) => <span data-testid="avatar">{props.name}</span>,
+}));
+
+describe('SelectableAvatar', () => {
+  it('renders the wrapped avatar', () => {
+    render(<SelectableAvatar name="Marta" checked={false} onToggle={() => {}} selectLabel="Select" />);
+    expect(screen.getByTestId('avatar')).toHaveTextContent('Marta');
+  });
+
+  it('fires onToggle and stops propagation when the avatar is clicked', () => {
+    const onToggle = vi.fn();
+    const onRowClick = vi.fn();
+    render(
+      <div onClick={onRowClick}>
+        <SelectableAvatar name="Marta" checked={false} onToggle={onToggle} selectLabel="Select" />
+      </div>,
+    );
+    fireEvent.click(screen.getByRole('checkbox'));
+    expect(onToggle).toHaveBeenCalledTimes(1);
+    // Clicking the avatar must not bubble up to open/select the row.
+    expect(onRowClick).not.toHaveBeenCalled();
+  });
+
+  it('reflects the checked state via aria-checked', () => {
+    const { rerender } = render(
+      <SelectableAvatar name="Marta" checked={false} onToggle={() => {}} selectLabel="Select" />,
+    );
+    expect(screen.getByRole('checkbox')).toHaveAttribute('aria-checked', 'false');
+    rerender(<SelectableAvatar name="Marta" checked onToggle={() => {}} selectLabel="Select" />);
+    expect(screen.getByRole('checkbox')).toHaveAttribute('aria-checked', 'true');
+  });
+});

components/email/email-list-item.tsx

@@ -5,7 +5,7 @@ import { useCallback } from "react";
 import { formatDate, stripInvisibleLeading } from "@/lib/utils";
 import { Email } from "@/lib/jmap/types";
 import { cn } from "@/lib/utils";
-import { Avatar } from "@/components/ui/avatar";
+import { SelectableAvatar } from "@/components/email/selectable-avatar";
 import { Paperclip, Star, Circle, CheckSquare, Square, Reply, Forward } from "lucide-react";
 import { useEmailStore } from "@/stores/email-store";
 import { useSettingsStore, KEYWORD_PALETTE } from "@/stores/settings-store";
@@ -34,6 +34,7 @@ interface EmailListItemProps {
 
 export function EmailListItem({ email, selected, onClick, onDoubleClick, onContextMenu, onToggleStar, onMarkAsRead, onDelete, onArchive, onSetColorTag, onMarkAsSpam, onUndoSpam }: EmailListItemProps) {
   const t = useTranslations('email_viewer');
+  const tBatch = useTranslations('email_list.batch_actions');
   const { selectedEmailIds, toggleEmailSelection, selectRangeEmails, selectedMailbox, mailboxes, clearSelection, isUnifiedView, unifiedRole } = useEmailStore();
   const showPreview = useSettingsStore((state) => state.showPreview);
   const density = useSettingsStore((state) => state.density);
@@ -180,12 +181,15 @@ export function EmailListItem({ email, selected, onClick, onDoubleClick, onConte
 
         {/* Avatar */}
         {density !== 'extra-compact' && (
-          <Avatar
+          <SelectableAvatar
             name={sender?.name}
             email={sender?.email}
             size={isFocusedMailLayout ? "sm" : "md"}
             className="flex-shrink-0 shadow-sm"
             disableImages={hideJunkAvatarImages}
+            checked={isChecked}
+            onToggle={() => toggleEmailSelection(email.id)}
+            selectLabel={tBatch('select')}
           />
         )}
 

components/email/selectable-avatar.tsx

@@ -0,0 +1,59 @@
+"use client";
+
+import type { ComponentProps } from "react";
+import { Check } from "lucide-react";
+import { Avatar } from "@/components/ui/avatar";
+import { cn } from "@/lib/utils";
+
+type SelectableAvatarProps = ComponentProps<typeof Avatar> & {
+  /** Whether the underlying message/thread is currently selected. */
+  checked: boolean;
+  /** Toggle selection. The wrapper stops propagation so the row is not opened. */
+  onToggle: () => void;
+  /** Accessible label for the selection control. */
+  selectLabel?: string;
+};
+
+/**
+ * Avatar that doubles as a selection control, Thunderbird-style: clicking the
+ * avatar toggles the message/thread into the current selection instead of
+ * opening it. A check overlay appears on hover (hinting it is clickable) and
+ * stays visible while the row is selected.
+ */
+export function SelectableAvatar({
+  checked,
+  onToggle,
+  selectLabel,
+  className,
+  ...avatarProps
+}: SelectableAvatarProps) {
+  return (
+    <button
+      type="button"
+      role="checkbox"
+      aria-checked={checked}
+      aria-label={selectLabel}
+      onClick={(e) => {
+        e.stopPropagation();
+        onToggle();
+      }}
+      className={cn(
+        "group/select relative shrink-0 rounded-full outline-none",
+        "focus-visible:ring-2 focus-visible:ring-primary/60",
+        className,
+      )}
+    >
+      <Avatar {...avatarProps} />
+      <span
+        aria-hidden
+        className={cn(
+          "absolute inset-0 flex items-center justify-center rounded-full",
+          "bg-primary text-primary-foreground transition-opacity duration-150",
+          checked ? "opacity-100" : "opacity-0 group-hover/select:opacity-100",
+        )}
+      >
+        <Check className="h-4 w-4" />
+      </span>
+    </button>
+  );
+}

components/email/thread-list-item.tsx

@@ -4,7 +4,7 @@ import React, { useCallback } from "react";
 import { formatDate, formatDateTime, stripInvisibleLeading } from "@/lib/utils";
 import { Email, ThreadGroup, ALL_MAIL_MAILBOX_ID } from "@/lib/jmap/types";
 import { cn } from "@/lib/utils";
-import { Avatar } from "@/components/ui/avatar";
+import { SelectableAvatar } from "@/components/email/selectable-avatar";
 import { Paperclip, Star, Circle, ChevronRight, ChevronDown, Loader2, MessageSquare, CheckSquare, Square, Reply, Forward, CalendarClock, Folder } from "lucide-react";
 import { useSettingsStore, KEYWORD_PALETTE } from "@/stores/settings-store";
 import { useUIStore } from "@/stores/ui-store";
@@ -75,6 +75,7 @@ interface SingleEmailItemProps {
 const SingleEmailItem = React.forwardRef<HTMLDivElement, SingleEmailItemProps>(
   function SingleEmailItem({ email, selected, onClick, onDoubleClick, onContextMenu, showPreview, colorTag, onToggleStar, onMarkAsRead, onDelete, onArchive, onSetColorTag, onMarkAsSpam, onUndoSpam }, ref) {
     const t = useTranslations('email_viewer');
+    const tBatch = useTranslations('email_list.batch_actions');
     const isUnread = !email.keywords?.$seen;
     const isStarred = email.keywords?.$flagged;
     const isAnswered = email.keywords?.$answered;
@@ -221,12 +222,15 @@ const SingleEmailItem = React.forwardRef<HTMLDivElement, SingleEmailItemProps>(
           )}
 
           {density !== 'extra-compact' && (
-            <Avatar
+            <SelectableAvatar
               name={sender?.name}
               email={sender?.email}
               size={isFocusedMailLayout ? "sm" : "md"}
               className="flex-shrink-0 shadow-sm"
               disableImages={hideJunkAvatarImages}
+              checked={isChecked}
+              onToggle={() => toggleEmailSelection(email.id)}
+              selectLabel={tBatch('select')}
             />
           )}
 
@@ -431,6 +435,7 @@ export const ThreadListItem = React.forwardRef<HTMLDivElement, ThreadListItemPro
   }, ref) {
     const t = useTranslations('threads');
     const tEmailViewer = useTranslations('email_viewer');
+    const tBatch = useTranslations('email_list.batch_actions');
     const showPreview = useSettingsStore((state) => state.showPreview);
     const density = useSettingsStore((state) => state.density);
     const mailLayout = useSettingsStore((state) => state.mailLayout);
@@ -515,13 +520,8 @@ export const ThreadListItem = React.forwardRef<HTMLDivElement, ThreadListItemPro
 
     const emailsToShow = expandedEmails || thread.emails;
 
-    const handleThreadCheckboxClick = (e: React.MouseEvent) => {
-      e.stopPropagation();
-      if (e.shiftKey) {
-        selectRangeEmails(latestEmail.id);
-        return;
-      }
-      // Toggle selection for all emails in this thread
+    // Toggle selection for all emails in this thread.
+    const toggleThreadSelection = () => {
       const allSelected = thread.emails.every(em => selectedEmailIds.has(em.id));
       const newSelection = new Set(selectedEmailIds);
       thread.emails.forEach(em => {
@@ -534,6 +534,15 @@ export const ThreadListItem = React.forwardRef<HTMLDivElement, ThreadListItemPro
       useEmailStore.setState({ selectedEmailIds: newSelection, lastSelectedEmailId: latestEmail.id });
     };
 
+    const handleThreadCheckboxClick = (e: React.MouseEvent) => {
+      e.stopPropagation();
+      if (e.shiftKey) {
+        selectRangeEmails(latestEmail.id);
+        return;
+      }
+      toggleThreadSelection();
+    };
+
     const handleHeaderClick = (e: React.MouseEvent) => {
       if (e.ctrlKey || e.metaKey) {
         e.preventDefault();
@@ -633,12 +642,15 @@ export const ThreadListItem = React.forwardRef<HTMLDivElement, ThreadListItemPro
 
             {density !== 'extra-compact' && (
               <div className="relative flex-shrink-0">
-                <Avatar
+                <SelectableAvatar
                   name={avatarPerson?.name}
                   email={avatarPerson?.email}
                   size={isFocusedMailLayout ? "sm" : "md"}
                   className="shadow-sm"
                   disableImages={hideJunkAvatarImages}
+                  checked={isChecked}
+                  onToggle={toggleThreadSelection}
+                  selectLabel={tBatch('select')}
                 />
                 {!isMobile && !isFocusedMailLayout && (
                   <button