diff --git a/components/email/__tests__/composer-plugin-surfaces.test.tsx b/components/email/__tests__/composer-plugin-surfaces.test.tsx
index f236cba0b..c9812f7c9 100644
--- a/components/email/__tests__/composer-plugin-surfaces.test.tsx
+++ b/components/email/__tests__/composer-plugin-surfaces.test.tsx
@@ -518,17 +518,19 @@ describe('composer-sidebar and composer-sidebar-right', () => {
     offerSlots('p1', ['composer-sidebar', 'composer-sidebar-right']);
     const { unmount } = render(<EmailComposer initialData={DRAFT} onClose={vi.fn()} />);
 
+    // A mouse drag, as pointer events with the button held (the handle follows pointers).
+    const drag = (handle: HTMLElement, from: number, to: number) => {
+      fireEvent.pointerDown(handle, { pointerId: 1, button: 0, buttons: 1, pointerType: 'mouse', clientX: from, clientY: 10 });
+      fireEvent.pointerMove(document, { pointerId: 1, buttons: 1, pointerType: 'mouse', clientX: to, clientY: 10 });
+      fireEvent.pointerUp(document, { pointerId: 1, button: 0, buttons: 0, pointerType: 'mouse' });
+    };
     // The right panel's handle is on its left edge: dragging left widens it.
     const right = screen.getByTestId('composer-sidebar-resize-right');
-    fireEvent.mouseDown(right, { clientX: 1000 });
-    fireEvent.mouseMove(document, { clientX: 900 });
-    fireEvent.mouseUp(document);
+    drag(right, 1000, 900);
     expect(panel('right').style.width).toBe('360px');
     // The left panel's handle is on its right edge: dragging left narrows it, down to the minimum.
     const left = screen.getByTestId('composer-sidebar-resize-left');
-    fireEvent.mouseDown(left, { clientX: 300 });
-    fireEvent.mouseMove(document, { clientX: 100 });
-    fireEvent.mouseUp(document);
+    drag(left, 300, 100);
     expect(panel('left').style.width).toBe('220px');
     fireEvent.keyDown(left, { key: 'ArrowRight' });
     expect(panel('left').style.width).toBe('230px');
diff --git a/components/email/email-composer.tsx b/components/email/email-composer.tsx
index cc9972586..211c89f6c 100644
--- a/components/email/email-composer.tsx
+++ b/components/email/email-composer.tsx
@@ -2753,6 +2753,17 @@ export function EmailComposer({
   const wantsPluginSelection = wantsPluginDraft;
   const [pluginSelection, setPluginSelection] = useState<{ text: string; empty: boolean }>(EMPTY_SELECTION);
   const [pluginEditor, setPluginEditor] = useState<Editor | null>(null);
+  // One callback for the composer's life: the editor reports itself ready
+  // whenever this changes, and every report now sets state, so a new arrow
+  // per render would report, render and report again without end.
+  const handleEditorReady = useCallback((ed: Editor) => {
+    editorRef.current = ed;
+    setPluginEditor(ed);
+    if (!replyFocusedRef.current && (mode === 'reply' || mode === 'replyAll')) {
+      replyFocusedRef.current = true;
+      ed.commands.focus('start');
+    }
+  }, [mode]);
   useEffect(() => {
     if (!wantsPluginSelection) return;
     let timer: ReturnType<typeof setTimeout> | null = null;
@@ -4158,14 +4169,7 @@ export function EmailComposer({
               hasError={validationErrors.body}
               collapseToolbarOnMobile={!showFormattingOnMobile}
               toolbarPlacement={mvWindow ? (mvShowFormatting ? 'bottom' : 'hidden') : 'top'}
-              onEditorReady={(ed) => {
-                editorRef.current = ed;
-                setPluginEditor(ed);
-                if (!replyFocusedRef.current && (mode === 'reply' || mode === 'replyAll')) {
-                  replyFocusedRef.current = true;
-                  ed.commands.focus('start');
-                }
-              }}
+              onEditorReady={handleEditorReady}
               mentionCandidates={recipientMentionsEnabled ? mentionCandidates : undefined}
               findMentionContacts={recipientMentionsEnabled && mentionAddsRecipientTo !== 'off' ? findMentionContacts : undefined}
               mentionAddsTo={mentionAddsRecipientTo === 'cc' ? 'cc' : 'to'}