fix(native-chat): sending brings the latest into view and follows the reply

src/renderer/src/components/native-chat/NativeChatComposer.tsx

@@ -66,6 +66,7 @@ const NativeChatComposerPane = forwardRef<NativeChatComposerHandle, NativeChatCo
       optimisticSendOutcome,
       onOptimisticSendCanceled,
       onSlashCommand,
+      onSubmitted,
       answerCommandLocally,
       onSwitchToTerminal,
       readTerminalScreen,
@@ -225,6 +226,7 @@ const NativeChatComposerPane = forwardRef<NativeChatComposerHandle, NativeChatCo
         agent,
         disabled,
         onSlashCommand,
+        onSubmitted,
         resolveTarget,
         setHistory
       })
@@ -255,30 +257,35 @@ const NativeChatComposerPane = forwardRef<NativeChatComposerHandle, NativeChatCo
       setCaret
     })
 
-    const sendPty = useNativeChatPtyComposerSend({
+    // What both terminal send paths share: where a command goes and what the composer resets.
+    const ptyCommandRouting = {
       agent,
-      draft,
-      imageAttachments,
       disabled,
       isDispatchingSessionOption,
-      launchDraft: launchSeed?.launchDraft,
-      launchDraftResolved: launchSeed?.launchDraftResolved === true,
-      readTerminalScreen,
       resolveTarget,
-      classifySend,
-      onOptimisticSend,
-      optimisticSendOutcome,
       onSlashCommand,
+      onSubmitted,
       answerCommandLocally,
       sessionOptionsSurface: ptySessionOptionsSurface,
-      terminalTabId,
       trackPendingSend,
       setHistory,
       setDraft,
       setCaret,
       clearSkillOrigin,
       clearImageAttachments,
       setNotice
+    }
+    const sendPty = useNativeChatPtyComposerSend({
+      ...ptyCommandRouting,
+      draft,
+      imageAttachments,
+      launchDraft: launchSeed?.launchDraft,
+      launchDraftResolved: launchSeed?.launchDraftResolved === true,
+      readTerminalScreen,
+      classifySend,
+      onOptimisticSend,
+      optimisticSendOutcome,
+      terminalTabId
     })
     const { send, goalMode } = useNativeChatComposerSubmit({
       structuredTransport,
@@ -303,21 +310,8 @@ const NativeChatComposerPane = forwardRef<NativeChatComposerHandle, NativeChatCo
     })
 
     const dispatchPtyPickerCommand = useNativeChatPickerCommandDispatch({
-      agent,
-      disabled,
-      isDispatchingSessionOption,
-      resolveTarget,
-      onSlashCommand,
-      answerCommandLocally,
-      sessionOptionsSurface: ptySessionOptionsSurface,
-      trackPendingSend,
-      setHistory,
-      setDraft,
-      setCaret,
-      setActiveSuggestion,
-      clearSkillOrigin,
-      clearImageAttachments,
-      setNotice
+      ...ptyCommandRouting,
+      setActiveSuggestion
     })
     const dispatchPickerCommand = useCallback(
       (command: Parameters<typeof dispatchPtyPickerCommand>[0]) =>

src/renderer/src/components/native-chat/NativeChatMessageList.growth-windowing.test.tsx

@@ -453,6 +453,7 @@ describe('transcript follow ownership across growth and appends', () => {
     const scheduleSpy = vi.spyOn(window, 'requestAnimationFrame')
     const scrollToSpy = vi.spyOn(scroller, 'scrollTo')
     const readingAt = 2000
+    fireEvent.wheel(scroller, { deltaY: -100 })
     scroller.scrollTop = readingAt
     fireEvent.scroll(scroller)
     expect(scrollToSpy).toHaveBeenLastCalledWith({ behavior: 'auto', top: readingAt })

src/renderer/src/components/native-chat/NativeChatMessageList.message-rail-windowing.test.tsx

@@ -26,7 +26,19 @@ afterEach(cleanup)
 describe('revealing a diff from a turn rollup', () => {
   let restoreLayout = (): void => {}
   beforeEach(() => {
-    restoreLayout = stubLayout()
+    restoreLayout = stubLayout({ scrollGeometry: true })
+    vi.spyOn(HTMLElement.prototype, 'getBoundingClientRect').mockImplementation(function (
+      this: HTMLElement
+    ) {
+      const row = this.closest<HTMLElement>('[data-index]')
+      const scroller = this.closest<HTMLElement>('[data-native-chat-scroll]')
+      return new DOMRect(
+        0,
+        row ? Number.parseFloat(row.style.top) - (scroller?.scrollTop ?? 0) : 0,
+        100,
+        this.offsetHeight
+      )
+    })
   })
   afterEach(() => {
     restoreLayout()
@@ -79,29 +91,47 @@ describe('revealing a diff from a turn rollup', () => {
     ].map((item, index) => ({ ...item, sequence: index + 1 }))
     const scrollTo = vi.fn()
     vi.spyOn(HTMLElement.prototype, 'scrollTo').mockImplementation(scrollTo)
-    const { container } = render(
+    const transcript = (): React.JSX.Element => (
       <NativeChatMessageList
         session={session(projectStructuredItemsToNativeChat(withPrompts))}
         journalItems={withPrompts}
         isWorking={false}
         expandSignal={false}
       />
     )
+    const { container, rerender } = render(transcript())
+    const selectedTop = Number.parseFloat(
+      screen.getByText('Second prompt').closest<HTMLElement>('[data-index]')?.style.top ?? ''
+    )
+    expect(selectedTop).toBeGreaterThan(0)
     fireEvent.click(screen.getByRole('button', { name: /1 changed file/ }))
     fireEvent.click(screen.getByRole('button', { name: /src\/a.ts/ }))
     scrollTranscript(container, 6000)
     expect(screen.getByText('Edited')).toBeInTheDocument()
     scrollTo.mockClear()
     fireEvent.click(screen.getByRole('button', { name: 'Your messages' }))
     fireEvent.click(screen.getByRole('button', { name: 'Second prompt' }))
-    expect(scrollTo).toHaveBeenCalledTimes(1)
+    expect(scrollTo.mock.calls).toEqual([
+      [{ top: 6000, behavior: 'auto' }],
+      [{ top: selectedTop, behavior: 'smooth' }]
+    ])
     expect(screen.queryByRole('button', { name: /^Edited .*a\.ts(?:\s|$)/ })).toBeNull()
+    scrollTo.mockClear()
+    rerender(transcript())
+    rerender(transcript())
+    expect(scrollTo).not.toHaveBeenCalled()
 
     scrollTranscript(container, 0)
     scrollTo.mockClear()
     fireEvent.click(screen.getByRole('button', { name: /1 changed file/ }))
     fireEvent.click(screen.getByRole('button', { name: /src\/a.ts/ }))
-    expect(scrollTo).toHaveBeenCalledTimes(1)
+    const diffTop = Number.parseFloat(
+      screen.getByText('Edited').closest<HTMLElement>('[data-index]')?.style.top ?? ''
+    )
+    expect(Number.isFinite(diffTop)).toBe(true)
+    expect(scrollTo.mock.calls.filter(([options]) => options?.behavior === 'smooth')).toEqual([
+      [{ top: diffTop, behavior: 'smooth' }]
+    ])
   })
 })
 

src/renderer/src/components/native-chat/NativeChatMessageList.rail-history-jump.test.tsx

@@ -435,6 +435,7 @@ describe('jumping from the rail while following the end', () => {
     await settle(10)
     // A reader parked above the end, so the button shows.
     act(() => {
+      fireEvent.wheel(scroller(), { deltaY: -100 })
       scroller().scrollTop = 200
     })
     await settle(2)
@@ -450,6 +451,29 @@ describe('jumping from the rail while following the end', () => {
     expect(screen.queryByText('prompt-5')).toBeNull()
     expect(distanceFromBottom()).toBe(0)
   })
+
+  it('jumps to a message without animating when the reader asks for reduced motion', async () => {
+    vi.spyOn(window, 'matchMedia').mockImplementation((query: string) => ({
+      matches: query === '(prefers-reduced-motion: reduce)',
+      media: query,
+      onchange: null,
+      addEventListener: () => {},
+      removeEventListener: () => {},
+      addListener: () => {},
+      removeListener: () => {},
+      dispatchEvent: () => false
+    }))
+    render(<PagedTranscript />)
+    await settle(10)
+
+    fireEvent.click(screen.getByRole('button', { name: 'Your messages' }))
+    await frame()
+    fireEvent.click(screen.getByRole('button', { name: 'prompt-45' }))
+    await frame()
+
+    // A smooth scroll would still be easing in here, a few pixels from where it started.
+    expect(Math.abs(rowOffsetFromViewportTop('prompt-45'))).toBeLessThanOrEqual(2)
+  })
 })
 
 describe('revealing a diff while a rail jump pages', () => {