fix(diff-comments): show save error and restore focus intelligently

- Toast error when draft submission fails, so users see why it didn't save
- Return focus to editor only if the card still holds it when save completes, preventing focus theft on slow saves

src/renderer/src/components/diff-comments/DiffCommentDraftCard.test.tsx

@@ -1,8 +1,11 @@
 // @vitest-environment happy-dom
 import { act, cleanup, fireEvent, render } from '@testing-library/react'
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import { toast } from 'sonner'
 import { DiffCommentDraftCard } from './DiffCommentDraftCard'
 
+vi.mock('sonner', () => ({ toast: { error: vi.fn(), success: vi.fn(), info: vi.fn() } }))
+
 describe('DiffCommentDraftCard', () => {
   let scrollHeight = 60
 
@@ -138,6 +141,24 @@ describe('DiffCommentDraftCard', () => {
     await act(async () => resolveSubmit(true))
   })
 
+  it('reports a rejected save to the user and re-enables the card', async () => {
+    const error = new Error('network down')
+    const onSubmit = vi.fn().mockRejectedValue(error)
+    const consoleError = vi.spyOn(console, 'error').mockImplementation(() => {})
+    const view = render(
+      <DiffCommentDraftCard lineNumber={10} onCancel={vi.fn()} onSubmit={onSubmit} />
+    )
+    fireEvent.change(view.getByRole('textbox'), { target: { value: 'Rejected note' } })
+
+    await act(async () => {
+      fireEvent.click(view.getByRole('button', { name: 'Add note' }))
+    })
+
+    expect(toast.error).toHaveBeenCalledWith('Failed to save comment')
+    expect(consoleError).toHaveBeenCalled()
+    expect(view.getByRole('button', { name: 'Add note' }).hasAttribute('disabled')).toBe(false)
+  })
+
   it('seeds and reports draft text so a re-anchored card can carry it', () => {
     const onBodyChange = vi.fn()
     const view = render(

src/renderer/src/components/diff-comments/DiffCommentDraftCard.tsx

@@ -157,6 +157,10 @@ export function DiffCommentDraftCard({
       }
     } catch (err) {
       console.error('Failed to submit diff comment draft:', err)
+      // A rejected save never reaches the caller's own failure toast, so report it here.
+      toast.error(
+        translate('auto.components.editor.diffCommentSaveFailed', 'Failed to save comment')
+      )
       if (mountedRef.current) {
         setSubmitting(false)
       }

src/renderer/src/components/diff-comments/diff-comment-draft-zone.test.tsx

@@ -200,6 +200,38 @@ describe('useDiffCommentDraftZone in-flight submit', () => {
   })
 })
 
+describe('useDiffCommentDraftZone focus handoff', () => {
+  it('returns focus to the editor when a save succeeds while the card holds it', async () => {
+    const fake = createFakeDiffCommentEditor()
+    const { onCreateComment, settle } = deferredCreateComment()
+    const hook = renderDraftZone(fake, onCreateComment)
+    openDraftAt(hook, DRAFT_LINE)
+    draftCard(fake).textarea.focus()
+    submitDraft(fake, BODY)
+
+    await settle(true)
+
+    expect(fake.zones.size).toBe(0)
+    expect(fake.focusCount()).toBe(1)
+  })
+
+  it('leaves focus alone when the save settles after the user clicked away', async () => {
+    const fake = createFakeDiffCommentEditor()
+    const { onCreateComment, settle } = deferredCreateComment()
+    const hook = renderDraftZone(fake, onCreateComment)
+    openDraftAt(hook, DRAFT_LINE)
+    submitDraft(fake, BODY)
+
+    const elsewhere = document.createElement('input')
+    document.body.appendChild(elsewhere)
+    elsewhere.focus()
+    await settle(true)
+
+    expect(fake.zones.size).toBe(0)
+    expect(fake.focusCount()).toBe(0)
+  })
+})
+
 describe('useDiffCommentDraftZone open state', () => {
   it('reports the draft closed again after cancel so the chord is not deadened', () => {
     const fake = createFakeDiffCommentEditor()

src/renderer/src/components/diff-comments/diff-comment-draft-zone.ts

@@ -199,7 +199,9 @@ export function useDiffCommentDraftZone({
               entry.submitting = false
               if (succeeded) {
                 if (draftZoneRef.current === entry) {
-                  disposeDraftZone()
+                  // Hand focus back to Monaco only if the card still holds it: a slow save can
+                  // settle after the user has clicked away, and stealing focus back is worse.
+                  disposeDraftZone(entry.domNode.contains(document.activeElement))
                 }
               } else if (draftZoneRef.current !== entry) {
                 restoreFailedSubmit(draft, body)

src/renderer/src/components/diff-comments/diff-comment-editor-test-fixture.ts

@@ -22,6 +22,8 @@ export type FakeDiffCommentEditor = {
   decorations: () => readonly FakeDecoration[]
   decorationWrites: () => number
   scrollTop: () => number
+  /** How many times the editor was asked to take focus back. */
+  focusCount: () => number
   emitMouseMove: (lineNumber: number) => void
   emitDispose: () => void
   /** Viewport-relative Y for a line, as the fake hit-test reads it. */
@@ -69,6 +71,7 @@ export function createFakeDiffCommentEditor(
   let scrollTop = 0
   let decorations: FakeDecoration[] = []
   let decorationWrites = 0
+  let focusCount = 0
   const mouseMoveListeners: ((e: { target: { position: { lineNumber: number } } }) => void)[] = []
   const disposeListeners: (() => void)[] = []
   const noopDisposable: IDisposable = { dispose: () => {} }
@@ -100,6 +103,9 @@ export function createFakeDiffCommentEditor(
     getScrollHeight: () => lineCount * FAKE_LINE_HEIGHT_PX,
     getLayoutInfo: () => ({ height: FAKE_EDITOR_HEIGHT_PX, contentLeft: 60 }),
     getSelection: () => null,
+    focus: () => {
+      focusCount += 1
+    },
     deltaDecorations: () => [],
     createDecorationsCollection: () => ({
       set: (next: MonacoEditor.IModelDeltaDecoration[]) => {
@@ -161,6 +167,7 @@ export function createFakeDiffCommentEditor(
     decorations: () => decorations,
     decorationWrites: () => decorationWrites,
     scrollTop: () => scrollTop,
+    focusCount: () => focusCount,
     clientYForLine,
     setLineCount: (next) => {
       lineCount = next