From 2ab2db91322b984ac02f01f1e1584571f0badc1a Mon Sep 17 00:00:00 2001
From: Jinwoo Hong <73622457+Jinwoo-H@users.noreply.github.com>
Date: Wed, 22 Apr 2026 00:28:56 -0400
Subject: [PATCH] fix(terminal): add proportional scroll fallback for sidebar
 resize (#901)

---
 src/renderer/src/App.tsx                      |  22 +-
 .../components/terminal-pane/pane-helpers.ts  |  12 +-
 .../terminal-pane/pty-connection.test.ts      |   4 +
 .../terminal-pane/pty-connection.ts           |  27 +
 .../use-terminal-pane-global-effects.ts       |  83 +-
 src/renderer/src/constants/terminal.ts        |   1 +
 src/renderer/src/hooks/useIpcEvents.test.ts   |   2 +-
 src/renderer/src/hooks/useIpcEvents.ts        |   3 +
 .../src/lib/pane-manager/pane-drag-scroll.ts  | 146 +++-
 .../src/lib/pane-manager/pane-lifecycle.ts    |  27 +-
 .../lib/pane-manager/pane-manager-types.ts    |  11 +
 .../src/lib/pane-manager/pane-manager.ts      |  85 +-
 .../src/lib/pane-manager/pane-scroll.ts       | 122 ++-
 .../src/lib/pane-manager/pane-tree-ops.ts     |  62 +-
 tests/e2e/fixtures/ink-tui-sim.mjs            |  72 ++
 tests/e2e/terminal-panes.spec.ts              | 771 ++++++++++++++++++
 16 files changed, 1358 insertions(+), 92 deletions(-)
 create mode 100644 tests/e2e/fixtures/ink-tui-sim.mjs

diff --git a/src/renderer/src/App.tsx b/src/renderer/src/App.tsx
index 2c3a4683c95..294186c87b8 100644
--- a/src/renderer/src/App.tsx
+++ b/src/renderer/src/App.tsx
@@ -3,7 +3,11 @@ import { useEffect, useLayoutEffect, useMemo, useRef, useState } from 'react'
 import { DEFAULT_STATUS_BAR_ITEMS, DEFAULT_WORKTREE_CARD_PROPERTIES } from '../../shared/constants'
 
 import { Minimize2, PanelLeft, PanelRight } from 'lucide-react'
-import { FOCUS_TERMINAL_PANE_EVENT, TOGGLE_TERMINAL_PANE_EXPAND_EVENT } from '@/constants/terminal'
+import {
+  FOCUS_TERMINAL_PANE_EVENT,
+  LAYOUT_WILL_CHANGE_EVENT,
+  TOGGLE_TERMINAL_PANE_EXPAND_EVENT
+} from '@/constants/terminal'
 import { syncZoomCSSVar } from '@/lib/ui-zoom'
 import { toast } from 'sonner'
 import { Toaster } from '@/components/ui/sonner'
@@ -499,6 +503,7 @@ function App(): React.JSX.Element {
       if (!e.altKey && !e.shiftKey && e.key.toLowerCase() === 'b') {
         dispatchClearModifierHints()
         e.preventDefault()
+        window.dispatchEvent(new Event(LAYOUT_WILL_CHANGE_EVENT))
         actions.toggleSidebar()
         return
       }
@@ -519,6 +524,7 @@ function App(): React.JSX.Element {
       if (!e.altKey && !e.shiftKey && e.key.toLowerCase() === 'l') {
         dispatchClearModifierHints()
         e.preventDefault()
+        window.dispatchEvent(new Event(LAYOUT_WILL_CHANGE_EVENT))
         actions.toggleRightSidebar()
         return
       }
@@ -527,6 +533,7 @@ function App(): React.JSX.Element {
       if (e.shiftKey && !e.altKey && e.key.toLowerCase() === 'e') {
         dispatchClearModifierHints()
         e.preventDefault()
+        window.dispatchEvent(new Event(LAYOUT_WILL_CHANGE_EVENT))
         actions.setRightSidebarTab('explorer')
         actions.setRightSidebarOpen(true)
         return
@@ -536,6 +543,7 @@ function App(): React.JSX.Element {
       if (e.shiftKey && !e.altKey && e.key.toLowerCase() === 'f') {
         dispatchClearModifierHints()
         e.preventDefault()
+        window.dispatchEvent(new Event(LAYOUT_WILL_CHANGE_EVENT))
         actions.setRightSidebarTab('search')
         actions.setRightSidebarOpen(true)
         return
@@ -552,6 +560,7 @@ function App(): React.JSX.Element {
         }
         dispatchClearModifierHints()
         e.preventDefault()
+        window.dispatchEvent(new Event(LAYOUT_WILL_CHANGE_EVENT))
         actions.setRightSidebarTab('source-control')
         actions.setRightSidebarOpen(true)
       }
@@ -597,7 +606,10 @@ function App(): React.JSX.Element {
           <TooltipTrigger asChild>
             <button
               className="sidebar-toggle"
-              onClick={actions.toggleSidebar}
+              onClick={() => {
+                window.dispatchEvent(new Event(LAYOUT_WILL_CHANGE_EVENT))
+                actions.toggleSidebar()
+              }}
               aria-label="Toggle sidebar"
             >
               <PanelLeft size={16} />
@@ -726,7 +738,10 @@ function App(): React.JSX.Element {
       <TooltipTrigger asChild>
         <button
           className="sidebar-toggle mr-2"
-          onClick={actions.toggleRightSidebar}
+          onClick={() => {
+            window.dispatchEvent(new Event(LAYOUT_WILL_CHANGE_EVENT))
+            actions.toggleRightSidebar()
+          }}
           aria-label="Toggle right sidebar"
         >
           <PanelRight size={16} />
@@ -742,6 +757,7 @@ function App(): React.JSX.Element {
     if (activeView === 'tasks' && rightSidebarOpen) {
       // Why: hide the right sidebar immediately when entering the tasks page
       // so a previous open state can't bleed into that distraction-free view.
+      window.dispatchEvent(new Event(LAYOUT_WILL_CHANGE_EVENT))
       actions.setRightSidebarOpen(false)
     }
   }, [activeView, rightSidebarOpen, actions])
diff --git a/src/renderer/src/components/terminal-pane/pane-helpers.ts b/src/renderer/src/components/terminal-pane/pane-helpers.ts
index dc38171eaf5..92ad5eb40cf 100644
--- a/src/renderer/src/components/terminal-pane/pane-helpers.ts
+++ b/src/renderer/src/components/terminal-pane/pane-helpers.ts
@@ -1,7 +1,8 @@
 import type { PaneManager } from '@/lib/pane-manager/pane-manager'
+import type { ScrollState } from '@/lib/pane-manager/pane-manager-types'
 
-export function fitPanes(manager: PaneManager): void {
-  manager.fitAllPanes()
+export function fitPanes(manager: PaneManager, preCapturedStates?: Map<number, ScrollState>): void {
+  manager.fitAllPanes(preCapturedStates)
 }
 
 /**
@@ -33,8 +34,11 @@ export function focusActivePane(manager: PaneManager): void {
   activePane?.terminal.focus()
 }
 
-export function fitAndFocusPanes(manager: PaneManager): void {
-  fitPanes(manager)
+export function fitAndFocusPanes(
+  manager: PaneManager,
+  preCapturedStates?: Map<number, ScrollState>
+): void {
+  fitPanes(manager, preCapturedStates)
   focusActivePane(manager)
 }
 
diff --git a/src/renderer/src/components/terminal-pane/pty-connection.test.ts b/src/renderer/src/components/terminal-pane/pty-connection.test.ts
index a414510ecbf..ee067612805 100644
--- a/src/renderer/src/components/terminal-pane/pty-connection.test.ts
+++ b/src/renderer/src/components/terminal-pane/pty-connection.test.ts
@@ -103,6 +103,10 @@ function createPane(paneId: number) {
     },
     fitAddon: {
       fit: vi.fn()
+    },
+    container: {
+      addEventListener: vi.fn(),
+      removeEventListener: vi.fn()
     }
   }
 }
diff --git a/src/renderer/src/components/terminal-pane/pty-connection.ts b/src/renderer/src/components/terminal-pane/pty-connection.ts
index 336f0c1a2f3..6d69d005133 100644
--- a/src/renderer/src/components/terminal-pane/pty-connection.ts
+++ b/src/renderer/src/components/terminal-pane/pty-connection.ts
@@ -192,10 +192,35 @@ export function connectPanePty(
     transport.sendInput(data)
   })
 
+  // Why: during divider drag, each fit() fires terminal.onResize which sends
+  // SIGWINCH to the PTY. Interactive programs (Claude Code) redraw on SIGWINCH,
+  // writing new content that corrupts scroll position between capture and
+  // restore. We fully suppress PTY resize during drag and store the latest
+  // pending dimensions. When the drag ends, `pane-drag-end` fires on the pane
+  // container and we flush the final dimensions in one shot — no debounce
+  // timer that could fire mid-drag if the user pauses.
+  let pendingDragResize: { cols: number; rows: number } | null = null
   const onResizeDisposable = pane.terminal.onResize(({ cols, rows }) => {
+    if (manager.isPaneDragResizing(pane.id)) {
+      pendingDragResize = { cols, rows }
+      return
+    }
     transport.resize(cols, rows)
   })
 
+  // Why: `unlockDragScroll` dispatches this event after clearing the drag
+  // scroll lock and restoring scroll state. At this point the terminal has
+  // its final dimensions from the last fit() but the PTY hasn't been told
+  // yet. Flush the pending resize so the PTY (and Claude Code) redraws at
+  // the correct size exactly once.
+  const onDragEnd = (): void => {
+    if (pendingDragResize) {
+      transport.resize(pendingDragResize.cols, pendingDragResize.rows)
+      pendingDragResize = null
+    }
+  }
+  pane.container.addEventListener('pane-drag-end', onDragEnd)
+
   // Defer PTY spawn/attach to next frame so FitAddon has time to calculate
   // the correct terminal dimensions from the laid-out container.
   deps.pendingWritesRef.current.set(pane.id, '')
@@ -493,6 +518,8 @@ export function connectPanePty(
         clearTimeout(startupInjectTimer)
         startupInjectTimer = null
       }
+      pane.container.removeEventListener('pane-drag-end', onDragEnd)
+      pendingDragResize = null
       if (connectFrame !== null) {
         // Why: StrictMode and split-group remounts can dispose a pane binding
         // before its deferred PTY attach/spawn work runs. Cancel that queued
diff --git a/src/renderer/src/components/terminal-pane/use-terminal-pane-global-effects.ts b/src/renderer/src/components/terminal-pane/use-terminal-pane-global-effects.ts
index 1e313e60ffe..df67ba9249f 100644
--- a/src/renderer/src/components/terminal-pane/use-terminal-pane-global-effects.ts
+++ b/src/renderer/src/components/terminal-pane/use-terminal-pane-global-effects.ts
@@ -1,10 +1,12 @@
 import { useEffect, useRef } from 'react'
 import {
   FOCUS_TERMINAL_PANE_EVENT,
+  LAYOUT_WILL_CHANGE_EVENT,
   TOGGLE_TERMINAL_PANE_EXPAND_EVENT,
   type FocusTerminalPaneDetail
 } from '@/constants/terminal'
 import type { PaneManager } from '@/lib/pane-manager/pane-manager'
+import type { ScrollState } from '@/lib/pane-manager/pane-manager-types'
 import { shellEscapePath } from './pane-helpers'
 import { fitAndFocusPanes, fitPanes, hasDimensionsChanged } from './pane-helpers'
 import type { PtyTransport } from './pty-transport'
@@ -69,13 +71,14 @@ export function useTerminalPaneGlobalEffects({
       return
     }
     if (isVisible) {
+      // Why: capture scroll states BEFORE resumeRendering() because WebGL
+      // context recreation and refresh() can fire xterm.js internal scroll
+      // events that corrupt viewportY. This is the same pre-corruption
+      // capture strategy used for sidebar toggles and divider drags.
+      const preResumeScrollStates = manager.captureAllScrollStates()
+
       // Why: resume WebGL immediately so the terminal shows its last-known
-      // state on the first painted frame. Without this, the browser paints
-      // 1+ frames of stale xterm DOM-fallback content at wrong dimensions
-      // (the "stretched" flash). On macOS, WebGL context creation is ~5 ms
-      // — fast enough to feel instant. On Windows (ANGLE → D3D11) it can
-      // take 100–500 ms, but the alternative (deferring to a rAF) leaves
-      // the terminal visibly distorted, which is a worse UX tradeoff.
+      // state on the first painted frame.
       manager.resumeRendering()
 
       fitEpochRef.current++
@@ -123,10 +126,10 @@ export function useTerminalPaneGlobalEffects({
         }
         fitRanForEpochRef.current = epoch
         if (isActive) {
-          fitAndFocusPanes(mgr)
+          fitAndFocusPanes(mgr, preResumeScrollStates)
           return
         }
-        fitPanes(mgr)
+        fitPanes(mgr, preResumeScrollStates)
       }
 
       if (entries.length === 0) {
@@ -253,28 +256,36 @@ export function useTerminalPaneGlobalEffects({
     // terminal running at a stale column count.
     const RESIZE_DEBOUNCE_MS = 150
     let timerId: ReturnType<typeof setTimeout> | null = null
+    // Why: scroll states must be captured at the instant the ResizeObserver
+    // fires, not 150ms later when the debounced fit runs. During the debounce
+    // window, async events (WebGL context loss, xterm.js Viewport._sync)
+    // can corrupt the scroll position, so a later capture would record the
+    // wrong viewportY. Capturing eagerly preserves the true pre-resize state.
+    let pendingScrollStates: Map<number, ScrollState> | null = null
     const resizeObserver = new ResizeObserver(() => {
+      const manager = managerRef.current
+      if (manager) {
+        pendingScrollStates = manager.captureAllScrollStates()
+      }
       if (timerId !== null) {
         clearTimeout(timerId)
       }
       timerId = setTimeout(() => {
         timerId = null
-        const manager = managerRef.current
-        if (!manager) {
+        const mgr = managerRef.current
+        if (!mgr) {
           return
         }
-        // Why: apply the same epoch-based deduplication as the isActive
-        // effect's rAF path.  Read the current epoch at fire time (not a
-        // captured value) because the ResizeObserver persists across the
-        // activation.  Dimension changes (e.g. window resize) bypass the
-        // dedup so legitimate refits are never suppressed.
         const currentEpoch = fitEpochRef.current
-        const dimensionsChanged = hasDimensionsChanged(manager)
+        const dimensionsChanged = hasDimensionsChanged(mgr)
         if (!dimensionsChanged && fitRanForEpochRef.current >= currentEpoch) {
+          pendingScrollStates = null
           return
         }
         fitRanForEpochRef.current = currentEpoch
-        fitPanes(manager)
+        const states = pendingScrollStates
+        pendingScrollStates = null
+        fitPanes(mgr, states ?? undefined)
       }, RESIZE_DEBOUNCE_MS)
     })
     resizeObserver.observe(container)
@@ -315,4 +326,42 @@ export function useTerminalPaneGlobalEffects({
       }
     })
   }, [isActiveRef, managerRef, paneTransportsRef])
+
+  // Why: instant layout changes (sidebar toggle via Cmd+L / Cmd+B) resize the
+  // terminal container synchronously. xterm.js fires internal scroll events on
+  // the viewport div during this synchronous reflow, corrupting scrollTop before
+  // any ResizeObserver callback can capture state. By locking scroll states in
+  // response to a synchronous event dispatched BEFORE the state change, we
+  // guarantee capture happens while the viewport is still at its original
+  // position — the same pattern that keeps divider drag scroll stable.
+  useEffect(() => {
+    let unlockTimer: ReturnType<typeof setTimeout> | null = null
+    const onLayoutWillChange = (): void => {
+      const manager = managerRef.current
+      if (!manager || !isVisibleRef.current) {
+        return
+      }
+      manager.lockAllScrollStates()
+      // Why: the sidebar CSS transition (200ms) + ResizeObserver debounce (150ms)
+      // means the final fitAllPanesInternal runs at ~350ms. The unlock must fire
+      // AFTER that fit so the locked state is used for the definitive restore.
+      // 500ms provides margin for CSS transition variance and frame scheduling.
+      // unlockAllScrollStates starts a 500ms settling rAF loop, so the lock
+      // actually persists until ~1000ms total, absorbing any SIGWINCH redraws.
+      if (unlockTimer !== null) {
+        clearTimeout(unlockTimer)
+      }
+      unlockTimer = setTimeout(() => {
+        unlockTimer = null
+        managerRef.current?.unlockAllScrollStates()
+      }, 500)
+    }
+    window.addEventListener(LAYOUT_WILL_CHANGE_EVENT, onLayoutWillChange)
+    return () => {
+      window.removeEventListener(LAYOUT_WILL_CHANGE_EVENT, onLayoutWillChange)
+      if (unlockTimer !== null) {
+        clearTimeout(unlockTimer)
+      }
+    }
+  }, [managerRef, isVisibleRef])
 }
diff --git a/src/renderer/src/constants/terminal.ts b/src/renderer/src/constants/terminal.ts
index 7b2f379ebb0..fba8e0b9713 100644
--- a/src/renderer/src/constants/terminal.ts
+++ b/src/renderer/src/constants/terminal.ts
@@ -1,5 +1,6 @@
 export const TOGGLE_TERMINAL_PANE_EXPAND_EVENT = 'orca-toggle-terminal-pane-expand'
 export const FOCUS_TERMINAL_PANE_EVENT = 'orca-focus-terminal-pane'
+export const LAYOUT_WILL_CHANGE_EVENT = 'orca-layout-will-change'
 
 export type ToggleTerminalPaneExpandDetail = {
   tabId: string
diff --git a/src/renderer/src/hooks/useIpcEvents.test.ts b/src/renderer/src/hooks/useIpcEvents.test.ts
index c0193122e23..b63303e98a6 100644
--- a/src/renderer/src/hooks/useIpcEvents.test.ts
+++ b/src/renderer/src/hooks/useIpcEvents.test.ts
@@ -1053,7 +1053,7 @@ describe('useIpcEvents shortcut hint clearing', () => {
     expect(dispatchEvent).toHaveBeenCalledWith(
       expect.objectContaining({ type: 'orca:clear-modifier-hints' })
     )
-    expect(dispatchEvent).toHaveBeenCalledTimes(2)
+    expect(dispatchEvent).toHaveBeenCalledTimes(3)
     expect(toggleSidebar).toHaveBeenCalledTimes(1)
     expect(activateAndRevealWorktree).toHaveBeenCalledWith('wt-2')
   })
diff --git a/src/renderer/src/hooks/useIpcEvents.ts b/src/renderer/src/hooks/useIpcEvents.ts
index 60ea1327842..25247c1fa12 100644
--- a/src/renderer/src/hooks/useIpcEvents.ts
+++ b/src/renderer/src/hooks/useIpcEvents.ts
@@ -16,6 +16,7 @@ import { dispatchZoomLevelChanged } from '@/lib/zoom-events'
 import { resolveZoomTarget } from './resolve-zoom-target'
 import { handleSwitchTab } from './ipc-tab-switch'
 import { dispatchClearModifierHints } from './useModifierHint'
+import { LAYOUT_WILL_CHANGE_EVENT } from '@/constants/terminal'
 import { isGitRepoKind } from '../../../shared/repo-kind'
 
 export { resolveZoomTarget } from './resolve-zoom-target'
@@ -47,6 +48,7 @@ export function useIpcEvents(): void {
     unsubs.push(
       window.api.ui.onToggleLeftSidebar(() => {
         dispatchClearModifierHints()
+        window.dispatchEvent(new Event(LAYOUT_WILL_CHANGE_EVENT))
         useAppStore.getState().toggleSidebar()
       })
     )
@@ -54,6 +56,7 @@ export function useIpcEvents(): void {
     unsubs.push(
       window.api.ui.onToggleRightSidebar(() => {
         dispatchClearModifierHints()
+        window.dispatchEvent(new Event(LAYOUT_WILL_CHANGE_EVENT))
         useAppStore.getState().toggleRightSidebar()
       })
     )
diff --git a/src/renderer/src/lib/pane-manager/pane-drag-scroll.ts b/src/renderer/src/lib/pane-manager/pane-drag-scroll.ts
index 74f4c533204..4be968d4f9e 100644
--- a/src/renderer/src/lib/pane-manager/pane-drag-scroll.ts
+++ b/src/renderer/src/lib/pane-manager/pane-drag-scroll.ts
@@ -1,4 +1,4 @@
-import type { ManagedPaneInternal } from './pane-manager-types'
+import type { ManagedPaneInternal, ScrollState } from './pane-manager-types'
 import { captureScrollState, restoreScrollState } from './pane-scroll'
 
 // ---------------------------------------------------------------------------
@@ -14,17 +14,159 @@ export function lockDragScroll(el: HTMLElement, panes: Map<number, ManagedPaneIn
   }
 }
 
+// Why: SIGWINCH settling delay. After the drag ends we flush the suppressed
+// PTY resize, which sends SIGWINCH to the shell. Interactive TUIs (Claude
+// Code / Ink) redraw on SIGWINCH, writing cursor-positioned content that
+// moves xterm's viewportY. If we clear pendingDragScrollState immediately,
+// the ResizeObserver's captureAllPaneScrollStates runs against the corrupted
+// viewportY and cements the wrong position. Keeping the lock active for
+// this period makes captureAllPaneScrollStates skip the pane and makes
+// safeFit / fitAllPanesInternal restore from the original captured state.
+const SIGWINCH_SETTLE_MS = 500
+
 export function unlockDragScroll(el: HTMLElement, panes: Map<number, ManagedPaneInternal>): void {
   for (const pane of findManagedPanesUnder(el, panes)) {
     if (pane.pendingDragScrollState) {
+      const originalState = pane.pendingDragScrollState
+
       try {
-        restoreScrollState(pane.terminal, pane.pendingDragScrollState)
+        restoreScrollState(pane.terminal, originalState)
+      } catch {
+        /* ignore */
+      }
+
+      // Why: during divider drag, PTY resize is suppressed to prevent
+      // SIGWINCH-driven redraws from corrupting scroll state. Dispatch
+      // on the pane container so pty-connection.ts can flush the final
+      // dimensions to the PTY when the drag ends.
+      pane.container.dispatchEvent(new CustomEvent('pane-drag-end'))
+
+      // Why: the PTY resize we just flushed causes SIGWINCH → Claude
+      // Code / Ink redraws → viewportY corruption. We keep the lock
+      // and actively restore scroll every frame during the settling
+      // period so the user never sees the viewport jump. Without this,
+      // there is a visible flash where the viewport jumps to line 0
+      // before the settling timeout fires.
+      startSettlingLoop(pane, originalState)
+    }
+  }
+}
+
+function startSettlingLoop(pane: ManagedPaneInternal, originalState: ScrollState): void {
+  let rafId: number | null = null
+
+  const restoreFrame = (): void => {
+    if (pane.pendingDragScrollState !== originalState) {
+      return
+    }
+    try {
+      restoreScrollState(pane.terminal, originalState)
+    } catch {
+      /* ignore */
+    }
+    rafId = requestAnimationFrame(restoreFrame)
+  }
+  rafId = requestAnimationFrame(restoreFrame)
+
+  setTimeout(() => {
+    if (rafId !== null) {
+      cancelAnimationFrame(rafId)
+    }
+    if (pane.pendingDragScrollState === originalState) {
+      try {
+        restoreScrollState(pane.terminal, originalState)
       } catch {
         /* ignore */
       }
       pane.pendingDragScrollState = null
+      // Why: during the settling period isPaneDragResizing was true,
+      // so any terminal.onResize events were suppressed and stored as
+      // pending. Dispatch pane-drag-end again so pty-connection.ts
+      // flushes any accumulated resize to the PTY.
+      pane.container.dispatchEvent(new CustomEvent('pane-drag-end'))
+    }
+  }, SIGWINCH_SETTLE_MS)
+}
+
+export function captureAllPaneScrollStates(
+  panes: Map<number, ManagedPaneInternal>
+): Map<number, ScrollState> {
+  const states = new Map<number, ScrollState>()
+  for (const pane of panes.values()) {
+    if (
+      !pane.pendingSplitScrollState &&
+      !pane.pendingDragScrollState &&
+      !pane.pendingLayoutScrollState
+    ) {
+      states.set(pane.id, captureScrollState(pane.terminal))
     }
   }
+  return states
+}
+
+export function lockAllPaneScrollStates(panes: Map<number, ManagedPaneInternal>): void {
+  for (const pane of panes.values()) {
+    if (
+      !pane.pendingSplitScrollState &&
+      !pane.pendingDragScrollState &&
+      !pane.pendingLayoutScrollState
+    ) {
+      pane.pendingLayoutScrollState = captureScrollState(pane.terminal)
+    }
+  }
+}
+
+export function unlockAllPaneScrollStates(panes: Map<number, ManagedPaneInternal>): void {
+  for (const pane of panes.values()) {
+    if (pane.pendingLayoutScrollState) {
+      const originalState = pane.pendingLayoutScrollState
+
+      try {
+        restoreScrollState(pane.terminal, originalState)
+      } catch {
+        /* ignore */
+      }
+
+      // Why: PTY resize is NOT suppressed during layout changes (unlike
+      // drag), so SIGWINCH fires immediately when fit() runs. Interactive
+      // TUIs (Claude Code / Ink) redraw on SIGWINCH, corrupting viewportY.
+      // The settling loop restores scroll every frame for 500ms, absorbing
+      // these redraws. The lock stays active so fitAllPanesInternal
+      // continues using the original captured state during settling.
+      startLayoutSettlingLoop(pane, originalState)
+    }
+  }
+}
+
+function startLayoutSettlingLoop(pane: ManagedPaneInternal, originalState: ScrollState): void {
+  let rafId: number | null = null
+
+  const restoreFrame = (): void => {
+    if (pane.pendingLayoutScrollState !== originalState) {
+      return
+    }
+    try {
+      restoreScrollState(pane.terminal, originalState)
+    } catch {
+      /* ignore */
+    }
+    rafId = requestAnimationFrame(restoreFrame)
+  }
+  rafId = requestAnimationFrame(restoreFrame)
+
+  setTimeout(() => {
+    if (rafId !== null) {
+      cancelAnimationFrame(rafId)
+    }
+    if (pane.pendingLayoutScrollState === originalState) {
+      try {
+        restoreScrollState(pane.terminal, originalState)
+      } catch {
+        /* ignore */
+      }
+      pane.pendingLayoutScrollState = null
+    }
+  }, SIGWINCH_SETTLE_MS)
 }
 
 function findManagedPanesUnder(
diff --git a/src/renderer/src/lib/pane-manager/pane-lifecycle.ts b/src/renderer/src/lib/pane-manager/pane-lifecycle.ts
index 335fd4ad9e8..6fc5841b21b 100644
--- a/src/renderer/src/lib/pane-manager/pane-lifecycle.ts
+++ b/src/renderer/src/lib/pane-manager/pane-lifecycle.ts
@@ -135,7 +135,8 @@ export function createPaneDOM(
     webglAddon: null,
     compositionHandler: null,
     pendingSplitScrollState: null,
-    pendingDragScrollState: null
+    pendingDragScrollState: null,
+    pendingLayoutScrollState: null
   }
 
   // Focus handler: clicking a pane makes it active and explicitly focuses
@@ -277,6 +278,9 @@ export function attachWebgl(pane: ManagedPaneInternal): void {
           } else if (pane.pendingDragScrollState) {
             pane.fitAddon.fit()
             restoreScrollState(pane.terminal, pane.pendingDragScrollState)
+          } else if (pane.pendingLayoutScrollState) {
+            pane.fitAddon.fit()
+            restoreScrollState(pane.terminal, pane.pendingLayoutScrollState)
           } else {
             const scrollState = captureScrollState(pane.terminal)
             pane.fitAddon.fit()
@@ -342,3 +346,24 @@ export function disposePane(
   }
   panes.delete(pane.id)
 }
+
+export function suspendAllRendering(panes: Map<number, ManagedPaneInternal>): void {
+  for (const pane of panes.values()) {
+    disposeWebgl(pane)
+  }
+}
+
+export function resumeAllRendering(panes: Map<number, ManagedPaneInternal>): void {
+  for (const pane of panes.values()) {
+    if (pane.gpuRenderingEnabled && !pane.webglAddon) {
+      attachWebgl(pane)
+      // Why: fresh WebGL canvas from attachWebgl() has no painted content;
+      // without refresh the terminal appears frozen when dims are unchanged.
+      try {
+        pane.terminal.refresh(0, pane.terminal.rows - 1)
+      } catch {
+        /* ignore */
+      }
+    }
+  }
+}
diff --git a/src/renderer/src/lib/pane-manager/pane-manager-types.ts b/src/renderer/src/lib/pane-manager/pane-manager-types.ts
index 1d5d0147352..5660438550f 100644
--- a/src/renderer/src/lib/pane-manager/pane-manager-types.ts
+++ b/src/renderer/src/lib/pane-manager/pane-manager-types.ts
@@ -53,6 +53,12 @@ export type ScrollState = {
   firstVisibleLineContent: string
   viewportY: number
   totalLines: number
+  cols: number
+  // Why: number of wrapped rows between the logical line start and the
+  // viewport row. When the anchor is the logical line start (not the
+  // viewport row itself), this offset lets restoreScrollState approximate
+  // the correct viewport position after reflow changes wrap points.
+  logicalLineOffset: number
 }
 
 export type ManagedPaneInternal = {
@@ -77,6 +83,11 @@ export type ManagedPaneInternal = {
   // terminal to a completely wrong position. Capturing once at drag start
   // and reusing that state for every restore eliminates accumulation.
   pendingDragScrollState: ScrollState | null
+  // Why: sidebar toggles and worktree switches resize the terminal container
+  // synchronously, corrupting scroll before ResizeObserver fires. Separate
+  // from pendingDragScrollState so a keyboard sidebar toggle during an active
+  // divider drag doesn't steal the drag's lock.
+  pendingLayoutScrollState: ScrollState | null
 } & ManagedPane
 
 export type DropZone = 'top' | 'bottom' | 'left' | 'right'
diff --git a/src/renderer/src/lib/pane-manager/pane-manager.ts b/src/renderer/src/lib/pane-manager/pane-manager.ts
index 7a3373c3b6e..9f3be4f0a73 100644
--- a/src/renderer/src/lib/pane-manager/pane-manager.ts
+++ b/src/renderer/src/lib/pane-manager/pane-manager.ts
@@ -1,9 +1,11 @@
+/* oxlint-disable max-lines */
 import type {
   PaneManagerOptions,
   PaneStyleOptions,
   ManagedPane,
   ManagedPaneInternal,
-  DropZone
+  DropZone,
+  ScrollState
 } from './pane-manager-types'
 import {
   createDivider,
@@ -22,7 +24,9 @@ import {
   openTerminal,
   attachWebgl,
   disposeWebgl,
-  disposePane
+  disposePane,
+  suspendAllRendering,
+  resumeAllRendering
 } from './pane-lifecycle'
 import { shouldFollowMouseFocus } from './focus-follows-mouse'
 import {
@@ -35,7 +39,13 @@ import {
   captureScrollState,
   refitPanesUnder
 } from './pane-tree-ops'
-import { lockDragScroll, unlockDragScroll } from './pane-drag-scroll'
+import {
+  lockDragScroll,
+  unlockDragScroll,
+  captureAllPaneScrollStates,
+  lockAllPaneScrollStates,
+  unlockAllPaneScrollStates
+} from './pane-drag-scroll'
 import { scheduleSplitScrollRestore } from './pane-split-scroll'
 
 export type { PaneManagerOptions, PaneStyleOptions, ManagedPane, DropZone }
@@ -182,8 +192,25 @@ export class PaneManager {
     return Array.from(this.panes.values()).map((p) => this.toPublic(p))
   }
 
-  fitAllPanes(): void {
-    fitAllPanesInternal(this.panes)
+  fitAllPanes(preCapturedStates?: Map<number, ScrollState>): void {
+    fitAllPanesInternal(this.panes, preCapturedStates)
+  }
+
+  captureAllScrollStates(): Map<number, ScrollState> {
+    return captureAllPaneScrollStates(this.panes)
+  }
+
+  lockAllScrollStates(): void {
+    lockAllPaneScrollStates(this.panes)
+  }
+
+  unlockAllScrollStates(): void {
+    unlockAllPaneScrollStates(this.panes)
+  }
+
+  isPaneDragResizing(paneId: number): boolean {
+    const pane = this.panes.get(paneId)
+    return pane?.pendingDragScrollState != null
   }
 
   getActivePane(): ManagedPane | null {
@@ -236,32 +263,13 @@ export class PaneManager {
   }
 
   suspendRendering(): void {
-    for (const pane of this.panes.values()) {
-      disposeWebgl(pane)
-    }
+    suspendAllRendering(this.panes)
   }
 
   resumeRendering(): void {
-    for (const pane of this.panes.values()) {
-      if (pane.gpuRenderingEnabled && !pane.webglAddon) {
-        attachWebgl(pane)
-        // Why: the fitPanes() optimization skips panes whose dimensions are
-        // unchanged (common when a worktree goes hidden→visible at the same
-        // window size). But the fresh WebGL canvas created by attachWebgl()
-        // has no painted content — without an explicit refresh the terminal
-        // appears frozen until something forces a dimension change (e.g. a
-        // split). This mirrors the onContextLoss handler in attachWebgl which
-        // calls the same refresh after falling back to the DOM renderer.
-        try {
-          pane.terminal.refresh(0, pane.terminal.rows - 1)
-        } catch {
-          /* ignore — pane may not be fully initialised yet */
-        }
-      }
-    }
+    resumeAllRendering(this.panes)
   }
 
-  /** Move a pane from its current position to a new position relative to a target pane. */
   movePane(sourcePaneId: number, targetPaneId: number, zone: DropZone): void {
     handlePaneDrop(sourcePaneId, targetPaneId, zone, this.dragState, this.getDragCallbacks())
   }
@@ -276,10 +284,6 @@ export class PaneManager {
     this.activePaneId = null
   }
 
-  // -----------------------------------------------------------------------
-  // Internal helpers
-  // -----------------------------------------------------------------------
-
   private createPaneInternal(): ManagedPaneInternal {
     const id = this.nextPaneId++
     const pane = createPaneDOM(
@@ -289,12 +293,8 @@ export class PaneManager {
       this.getDragCallbacks(),
       (paneId) => {
         if (!this.destroyed) {
-          // Why: split-pane layout/focus callbacks can leave the manager's
-          // activePaneId temporarily in sync while the browser's real focused
-          // xterm textarea is still on a different pane. Clicking a pane must
-          // always re-focus its terminal, even if the manager already thinks
-          // that pane is active; otherwise input can keep going to the wrong
-          // split after vertical/horizontal splits.
+          // Why: always re-focus on click — activePaneId can be stale after
+          // splits, sending input to the wrong pane without an explicit focus.
           this.setActivePane(paneId, { focus: true })
         }
       },
@@ -306,16 +306,8 @@ export class PaneManager {
     return pane
   }
 
-  /**
-   * Focus-follows-mouse entry point. Collects gate inputs from the manager
-   * and delegates to the pure gate helper.
-   *
-   * Invariant for future contributors: modal overlays (context menus, close
-   * dialogs, command palette) must be rendered as portals/siblings OUTSIDE
-   * the pane container. If a future overlay is ever rendered inside a .pane
-   * element, mouseenter will still fire on the pane underneath and this
-   * handler will incorrectly switch focus. Keep overlays out of the pane.
-   */
+  // Why: modal overlays must be rendered OUTSIDE .pane elements, otherwise
+  // mouseenter fires on the pane underneath and incorrectly switches focus.
   private handlePaneMouseEnter(paneId: number, event: MouseEvent): void {
     if (
       shouldFollowMouseFocus({
@@ -356,7 +348,6 @@ export class PaneManager {
     }
   }
 
-  /** Build the callbacks object for drag-reorder functions. */
   private getDragCallbacks() {
     return {
       getPanes: () => this.panes,
diff --git a/src/renderer/src/lib/pane-manager/pane-scroll.ts b/src/renderer/src/lib/pane-manager/pane-scroll.ts
index 6f430476246..db73b97f1d2 100644
--- a/src/renderer/src/lib/pane-manager/pane-scroll.ts
+++ b/src/renderer/src/lib/pane-manager/pane-scroll.ts
@@ -53,32 +53,128 @@ export function captureScrollState(terminal: Terminal): ScrollState {
   const buf = terminal.buffer.active
   const viewportY = buf.viewportY
   const wasAtBottom = viewportY >= buf.baseY
-  const firstVisibleLineContent = buf.getLine(viewportY)?.translateToString(true)?.trimEnd() ?? ''
   const totalLines = buf.baseY + terminal.rows
-  return { wasAtBottom, firstVisibleLineContent, viewportY, totalLines }
+
+  // Why: if the viewport starts at a wrapped continuation row, its content
+  // won't appear as a line start after reflow (column count change shifts
+  // wrap points). Walk backward to the logical line start — that content
+  // always remains a line start regardless of column width, making content
+  // matching reliable for long-line terminals like Claude Code.
+  let anchorY = viewportY
+  while (anchorY > 0 && buf.getLine(anchorY)?.isWrapped) {
+    anchorY--
+  }
+  const firstVisibleLineContent = buf.getLine(anchorY)?.translateToString(true)?.trimEnd() ?? ''
+  const logicalLineOffset = viewportY - anchorY
+
+  return {
+    wasAtBottom,
+    firstVisibleLineContent,
+    viewportY,
+    totalLines,
+    cols: terminal.cols,
+    logicalLineOffset
+  }
 }
 
 export function restoreScrollState(terminal: Terminal, state: ScrollState): void {
   if (state.wasAtBottom) {
-    terminal.scrollToBottom()
-    forceViewportScrollbarSync(terminal)
+    scrollToLineSync(terminal, terminal.buffer.active.baseY)
     return
   }
   const hintRatio = state.totalLines > 0 ? state.viewportY / state.totalLines : undefined
   const target = findLineByContent(terminal, state.firstVisibleLineContent, hintRatio)
   if (target >= 0) {
-    terminal.scrollToLine(target)
-    forceViewportScrollbarSync(terminal)
+    let scrollTarget = target
+    if (state.logicalLineOffset > 0) {
+      const newCols = terminal.cols
+      const scaledOffset =
+        state.cols > 0 && newCols > 0
+          ? Math.round(state.logicalLineOffset * (state.cols / newCols))
+          : state.logicalLineOffset
+      scrollTarget = Math.min(target + scaledOffset, terminal.buffer.active.baseY)
+    }
+    scrollToLineSync(terminal, scrollTarget)
+    return
+  }
+  if (hintRatio !== undefined) {
+    const newTotalLines = terminal.buffer.active.baseY + terminal.rows
+    const fallbackLine = Math.round(hintRatio * newTotalLines)
+    const clampedLine = Math.min(fallbackLine, terminal.buffer.active.baseY)
+    scrollToLineSync(terminal, clampedLine)
   }
 }
 
-// Why: xterm 6's Viewport._sync() updates scrollDimensions after resize but
-// skips the scrollPosition update when ydisp matches _latestYDisp (a stale
-// internal value). This leaves the scrollbar thumb at a wrong position even
-// though the rendered content is correct. A scroll jiggle (-1/+1) in the
-// same JS turn forces _sync() to fire with a differing ydisp, which triggers
-// setScrollPosition and syncs the scrollbar. No paint occurs between the two
-// synchronous calls so the intermediate state is never visible.
+// Why: the public terminal.scrollToLine(line) goes through
+// CoreBrowserTerminal.scrollLines → viewport.scrollLines, which calls
+// SmoothScrollableElement.setScrollPosition WITHOUT updating Viewport's
+// _latestYDisp. A subsequent queued _sync (from resize) then sees
+// ydisp === _latestYDisp (stale) and skips setScrollPosition, leaving the
+// SmoothScrollableElement's internal scrollTop out of sync with the buffer.
+// When the user later scrolls (mouse wheel), the SmoothScrollableElement
+// adjusts from its stale scrollTop, causing the terminal to jump.
+//
+// Viewport.scrollToLine(line, disableSmoothScroll=true) directly sets
+// _latestYDisp = line before calling setScrollPosition, keeping the
+// scrollbar state in sync. We access this through _core._viewport which
+// is an internal API (tested against @xterm/xterm 6.0.0). Falls back to
+// the public API + scroll jiggle if internals are unavailable.
+function scrollToLineSync(terminal: Terminal, line: number): void {
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  const viewport = (terminal as any)._core?._viewport
+  if (viewport && typeof viewport._sync === 'function') {
+    try {
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      const cellH = (terminal as any)._core?._renderService?.dimensions?.css?.cell?.height
+      const scrollableEl = viewport._scrollableElement
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      const bufLines = (terminal as any)._core?._bufferService?.buffer?.lines?.length
+
+      // Why: _sync(line) calls setScrollDimensions (possibly with stale
+      // renderer values) then setScrollPosition. If the stale dimensions
+      // give a maxScrollTop smaller than our target, the position is
+      // silently clamped. We call _sync first to let it do its thing,
+      // then OVERRIDE with correct dimensions computed from the actual
+      // buffer state, then re-set the scroll position. The second
+      // setScrollDimensions + setScrollPosition pair operates against
+      // accurate maxScrollTop so the target isn't clamped.
+      viewport._latestYDisp = undefined
+      viewport._sync(line)
+
+      if (
+        cellH &&
+        bufLines &&
+        scrollableEl?.setScrollDimensions &&
+        scrollableEl?.setScrollPosition
+      ) {
+        // Why: suppress _handleScroll during our dimension fix-up to
+        // prevent stale scroll events from overwriting buffer.ydisp.
+        viewport._suppressOnScrollHandler = true
+        scrollableEl.setScrollDimensions({
+          height: cellH * terminal.rows,
+          scrollHeight: cellH * bufLines
+        })
+        viewport._suppressOnScrollHandler = false
+
+        scrollableEl.setScrollPosition({ scrollTop: line * cellH })
+      }
+
+      viewport._latestYDisp = line
+    } catch {
+      terminal.scrollToLine(line)
+      forceViewportScrollbarSync(terminal)
+    }
+    return
+  }
+  terminal.scrollToLine(line)
+  forceViewportScrollbarSync(terminal)
+}
+
+// Why: fallback for when the internal viewport API is unavailable. The
+// scroll jiggle (-1/+1) triggers _handleScroll with diff≠0, which updates
+// _latestYDisp. Less reliable than the direct viewport.scrollToLine path
+// because it reads from the SmoothScrollableElement's potentially-stale
+// scrollTop, but better than nothing.
 function forceViewportScrollbarSync(terminal: Terminal): void {
   const buf = terminal.buffer.active
   if (buf.viewportY > 0) {
diff --git a/src/renderer/src/lib/pane-manager/pane-tree-ops.ts b/src/renderer/src/lib/pane-manager/pane-tree-ops.ts
index 3d860da6f2e..069043fa851 100644
--- a/src/renderer/src/lib/pane-manager/pane-tree-ops.ts
+++ b/src/renderer/src/lib/pane-manager/pane-tree-ops.ts
@@ -1,4 +1,9 @@
-import type { DropZone, ManagedPaneInternal, PaneStyleOptions } from './pane-manager-types'
+import type {
+  DropZone,
+  ManagedPaneInternal,
+  PaneStyleOptions,
+  ScrollState
+} from './pane-manager-types'
 import { createDivider } from './pane-divider'
 import { captureScrollState, restoreScrollState } from './pane-scroll'
 
@@ -26,7 +31,21 @@ export function safeFit(pane: ManagedPaneInternal): void {
     }
     if (pane.pendingDragScrollState) {
       pane.fitAddon.fit()
-      restoreScrollState(pane.terminal, pane.pendingDragScrollState)
+      // Why: fit() → resize() → queueSync() schedules a deferred _sync via
+      // addRefreshCallback that updates the Scrollable's dimensions in the next
+      // animation frame. Any scroll position we set synchronously here can be
+      // silently clamped when that deferred _sync calls setScrollDimensions
+      // (with _suppressOnScrollHandler=true, so clamping updates neither
+      // _latestYDisp nor buffer.ydisp). By scheduling our restore via the same
+      // addRefreshCallback mechanism, we run AFTER the deferred _sync has
+      // corrected the Scrollable dimensions, so our setScrollPosition operates
+      // against accurate maxScrollTop and isn't clamped.
+      deferredDragScrollRestore(pane)
+      return
+    }
+    if (pane.pendingLayoutScrollState) {
+      pane.fitAddon.fit()
+      restoreScrollState(pane.terminal, pane.pendingLayoutScrollState)
       return
     }
     const state = captureScrollState(pane.terminal)
@@ -37,7 +56,32 @@ export function safeFit(pane: ManagedPaneInternal): void {
   }
 }
 
-export function fitAllPanesInternal(panes: Map<number, ManagedPaneInternal>): void {
+function deferredDragScrollRestore(pane: ManagedPaneInternal): void {
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  const renderService = (pane.terminal as any)._core?._renderService
+  if (!renderService?.addRefreshCallback) {
+    if (pane.pendingDragScrollState) {
+      restoreScrollState(pane.terminal, pane.pendingDragScrollState)
+    }
+    return
+  }
+  renderService.addRefreshCallback(() => {
+    try {
+      const state = pane.pendingDragScrollState
+      if (!state) {
+        return
+      }
+      restoreScrollState(pane.terminal, state)
+    } catch {
+      /* pane may have been disposed */
+    }
+  })
+}
+
+export function fitAllPanesInternal(
+  panes: Map<number, ManagedPaneInternal>,
+  preCapturedStates?: Map<number, ScrollState>
+): void {
   for (const pane of panes.values()) {
     try {
       const dims = pane.fitAddon.proposeDimensions()
@@ -53,7 +97,17 @@ export function fitAllPanesInternal(panes: Map<number, ManagedPaneInternal>): vo
         restoreScrollState(pane.terminal, pane.pendingDragScrollState)
         continue
       }
-      const state = captureScrollState(pane.terminal)
+      if (pane.pendingLayoutScrollState) {
+        pane.fitAddon.fit()
+        restoreScrollState(pane.terminal, pane.pendingLayoutScrollState)
+        continue
+      }
+      // Why: use pre-captured state when available because the ResizeObserver
+      // debounce (150ms) gives async events (WebGL context loss, viewport
+      // _sync) time to corrupt the scroll position before we run. Capturing
+      // at the instant the ResizeObserver fires preserves the true pre-resize
+      // viewport position.
+      const state = preCapturedStates?.get(pane.id) ?? captureScrollState(pane.terminal)
       pane.fitAddon.fit()
       restoreScrollState(pane.terminal, state)
     } catch {
diff --git a/tests/e2e/fixtures/ink-tui-sim.mjs b/tests/e2e/fixtures/ink-tui-sim.mjs
new file mode 100644
index 00000000000..9f3c52335b2
--- /dev/null
+++ b/tests/e2e/fixtures/ink-tui-sim.mjs
@@ -0,0 +1,72 @@
+/**
+ * Simulates Ink's (React for CLI) inline viewport rendering behavior.
+ *
+ * Ink renders inline in the normal terminal buffer (not the alt screen).
+ * On SIGWINCH it re-renders by:
+ *   1. Moving cursor up to the start of the previous render
+ *   2. Clearing from cursor to end of display (\033[J)
+ *   3. Writing the new rendered output
+ *
+ * This is the exact pattern that causes scroll position corruption during
+ * divider drag resize, because the clear + rewrite sequence moves xterm.js's
+ * viewportY when the terminal has scrollback content above the render area.
+ *
+ * Usage: node tests/e2e/fixtures/ink-tui-sim.mjs
+ * Exits cleanly on SIGTERM or SIGINT.
+ */
+
+const TUI_HEIGHT = 12
+
+let lastLineCount = 0
+
+function render() {
+  const { columns: cols, rows } = process.stdout
+
+  // Step 1: if we previously rendered, move cursor back to start of that render
+  if (lastLineCount > 0) {
+    process.stdout.write(`\x1b[${lastLineCount}A\r`)
+  }
+
+  // Step 2: clear from cursor to end of display (exactly what Ink does)
+  process.stdout.write('\x1b[J')
+
+  // Step 3: write the TUI content
+  const lines = []
+  const hr = '━'.repeat(Math.min(cols, 80))
+  lines.push(`\x1b[1m${hr}\x1b[0m`)
+  lines.push(`  \x1b[36m◆\x1b[0m Claude Code  \x1b[2mv2.1.10\x1b[0m`)
+  lines.push(`  \x1b[2mModel: claude-sonnet-4-20250514\x1b[0m`)
+  lines.push('')
+  lines.push(`  \x1b[33m⠋\x1b[0m Thinking...`)
+  lines.push('')
+
+  // Fill remaining TUI height with status lines
+  const used = lines.length
+  for (let i = used; i < TUI_HEIGHT - 2; i++) {
+    const pad = ' '.repeat(Math.max(0, Math.min(cols, 80) - 30))
+    lines.push(`  \x1b[2mcontext: ${cols}×${rows} │ tokens: ${1234 + i}${pad}\x1b[0m`)
+  }
+
+  lines.push(`\x1b[1m${hr}\x1b[0m`)
+  lines.push(
+    `\x1b[7m ${' '.repeat(Math.max(0, Math.min(cols, 80) - 22))}` +
+      `${cols}×${rows} | Ctrl+C to exit \x1b[0m`
+  )
+
+  const output = `${lines.join('\n')}\n`
+  process.stdout.write(output)
+  lastLineCount = lines.length
+}
+
+// Initial render
+render()
+
+// Re-render on SIGWINCH (terminal resize) — this is the critical behavior
+process.on('SIGWINCH', render)
+
+// Clean exit
+process.on('SIGTERM', () => process.exit(0))
+process.on('SIGINT', () => process.exit(0))
+
+// Keep alive
+setInterval(() => {}, 60_000)
diff --git a/tests/e2e/terminal-panes.spec.ts b/tests/e2e/terminal-panes.spec.ts
index 2df63557eb9..da4afdb11cb 100644
--- a/tests/e2e/terminal-panes.spec.ts
+++ b/tests/e2e/terminal-panes.spec.ts
@@ -1,3 +1,4 @@
+/* oxlint-disable max-lines, curly */
 /**
  * E2E tests for terminal pane splitting, state retention, resizing, and closing.
  *
@@ -33,6 +34,7 @@ import {
   ensureTerminalVisible
 } from './helpers/store'
 import { pressShortcut } from './helpers/shortcuts'
+import path from 'path'
 
 // Why: only the pointer-drag resize test needs a visible window (pointer
 // capture requires a real pointer id). Every other pane operation here is
@@ -280,6 +282,775 @@ test.describe('Terminal Panes', () => {
       .toBe(true)
   })
 
+  /**
+   * Regression test: dragging a vertical divider to resize split panes must
+   * preserve scroll position in partially-scrolled terminals. The bug manifests
+   * as terminals jumping to the top (or near-top) during/after drag.
+   *
+   * Why headful: pointer capture requires a real pointer ID from a visible window.
+   */
+  test('@headful scroll position preserved during divider drag resize', async ({ orcaPage }) => {
+    await splitActiveTerminalPane(orcaPage, 'vertical')
+    await waitForPaneCount(orcaPage, 2)
+
+    const ptyId = await discoverActivePtyId(orcaPage)
+    // Why: long lines that wrap are essential to reproduce the bug. Short
+    // lines (like `seq 1 5000`) don't wrap, so baseY stays constant during
+    // reflow and scroll preservation is trivially correct. Claude Code output
+    // contains long formatted lines that reflow dramatically on column changes.
+    // Simulate Claude Code-like output: ANSI-formatted text with unicode
+    // box-drawing characters and long wrapped lines, similar to what Claude
+    // Code renders in a real session.
+    await execInTerminal(
+      orcaPage,
+      ptyId,
+      `python3 -c "
+import sys
+# Banner like Claude Code
+print('\\033[1;36m ▐▛███▜▌   Claude Code v2.1.10\\033[0m')
+print('\\033[90m' + '─' * 200 + '\\033[0m')
+# Simulated conversation with long wrapped lines
+for i in range(500):
+    if i % 10 == 0:
+        print(f'\\033[1;32m❯ User message {i//10}:\\033[0m')
+        print('  ' + 'Here is a long user prompt that wraps across multiple lines. ' * 4)
+    else:
+        # Code block with indentation
+        print(f'\\033[90m  {i:4d} │\\033[0m  ' + 'const result = await fetch(url).then(r => r.json()).catch(err => console.error(err)); // ' + 'x' * 80)
+print('\\033[90m' + '─' * 200 + '\\033[0m')
+print('DONE_MARKER')
+"`
+    )
+    await waitForTerminalOutput(orcaPage, 'DONE_MARKER', 15_000)
+    await orcaPage.waitForTimeout(500)
+
+    // Scroll to ~middle of scrollback
+    const scrollBefore = await orcaPage.evaluate(() => {
+      const tabId = (() => {
+        const store = window.__store
+        if (!store) return null
+        const state = store.getState()
+        const wId = state.activeWorktreeId
+        if (!wId) return null
+        return (state.tabsByWorktree[wId] ?? [])[0]?.id ?? null
+      })()
+      if (!tabId) return null
+      const manager = window.__paneManagers?.get(tabId)
+      if (!manager) return null
+      const pane = manager.getActivePane()
+      if (!pane) return null
+      const buf = pane.terminal.buffer.active
+      const targetLine = Math.floor(buf.baseY / 2)
+      pane.terminal.scrollToLine(targetLine)
+      return {
+        viewportY: pane.terminal.buffer.active.viewportY,
+        baseY: buf.baseY,
+        paneId: pane.id,
+        cols: pane.terminal.cols
+      }
+    })
+    expect(scrollBefore).not.toBeNull()
+    expect(scrollBefore!.viewportY).toBeGreaterThan(0)
+
+    // Capture renderer console logs for diagnostics
+    const consoleLogs: string[] = []
+    orcaPage.on('console', (msg) => {
+      const text = msg.text()
+      if (text.includes('[restoreScrollState]') || text.includes('[scrollToLineSync]')) {
+        consoleLogs.push(text)
+      }
+    })
+
+    // Drag the divider LEFT then RIGHT then LEFT — simulating the user's
+    // "adjust right and left" gesture. Each direction change causes reflow.
+    const divider = orcaPage.locator('.pane-divider.is-vertical').first()
+    await expect(divider).toBeVisible({ timeout: 3_000 })
+    const box = await divider.boundingBox()
+    expect(box).not.toBeNull()
+    const startX = box!.x + box!.width / 2
+    const startY = box!.y + box!.height / 2
+    await orcaPage.mouse.move(startX, startY)
+    await orcaPage.mouse.down()
+    // Drag left (narrowing), then right (widening), then left again
+    await orcaPage.mouse.move(startX - 250, startY, { steps: 20 })
+    await orcaPage.mouse.move(startX + 150, startY, { steps: 20 })
+    await orcaPage.mouse.move(startX - 200, startY, { steps: 20 })
+    await orcaPage.mouse.up()
+    await orcaPage.waitForTimeout(500)
+
+    const scrollAfter = await orcaPage.evaluate(
+      ({ paneId }) => {
+        const tabId = (() => {
+          const store = window.__store
+          if (!store) return null
+          const state = store.getState()
+          const wId = state.activeWorktreeId
+          if (!wId) return null
+          return (state.tabsByWorktree[wId] ?? [])[0]?.id ?? null
+        })()
+        if (!tabId) return null
+        const manager = window.__paneManagers?.get(tabId)
+        if (!manager) return null
+        const panes = manager.getPanes() ?? []
+        const pane = panes.find((p: { id: number }) => p.id === paneId)
+        if (!pane) return null
+        return {
+          viewportY: pane.terminal.buffer.active.viewportY,
+          baseY: pane.terminal.buffer.active.baseY,
+          cols: pane.terminal.cols
+        }
+      },
+      { paneId: scrollBefore!.paneId }
+    )
+    expect(scrollAfter).not.toBeNull()
+    const drift = Math.abs(scrollAfter!.viewportY - scrollBefore!.viewportY)
+    // Use proportional position (viewportY / baseY) since absolute line
+    // numbers change legitimately during reflow (more/less wrapping).
+    const ratioBefore = scrollBefore!.viewportY / scrollBefore!.baseY
+    const ratioAfter = scrollAfter!.baseY > 0 ? scrollAfter!.viewportY / scrollAfter!.baseY : 0
+    const proportionalDrift = Math.abs(ratioAfter - ratioBefore)
+    console.log(
+      '[scroll-test] wrapping-content:',
+      JSON.stringify({
+        before: scrollBefore!.viewportY,
+        after: scrollAfter!.viewportY,
+        absoluteDrift: drift,
+        ratioBefore: ratioBefore.toFixed(4),
+        ratioAfter: ratioAfter.toFixed(4),
+        proportionalDrift: proportionalDrift.toFixed(4),
+        baseYBefore: scrollBefore!.baseY,
+        baseYAfter: scrollAfter!.baseY,
+        colsBefore: scrollBefore!.cols,
+        colsAfter: scrollAfter!.cols
+      })
+    )
+    // Proportional drift should be <5% — the same relative content should
+    // be visible regardless of how wrapping changed the absolute line count.
+    expect(proportionalDrift).toBeLessThanOrEqual(0.05)
+    // Must not be at the very top
+    expect(scrollAfter!.viewportY).toBeGreaterThan(scrollAfter!.baseY * 0.1)
+
+    // Check for Scrollable desync: do a small mouse wheel scroll and verify
+    // the viewport doesn't jump to a completely different position.
+    const paneEl = orcaPage.locator(`.pane[data-pane-id="${scrollBefore!.paneId}"]`).first()
+    const paneBox = await paneEl.boundingBox()
+    if (paneBox) {
+      await orcaPage.mouse.move(paneBox.x + paneBox.width / 2, paneBox.y + paneBox.height / 2)
+      await orcaPage.mouse.wheel(0, 50) // scroll down slightly
+      await orcaPage.waitForTimeout(200)
+
+      const scrollAfterWheel = await orcaPage.evaluate(
+        ({ paneId }) => {
+          const tabId = (() => {
+            const store = window.__store
+            if (!store) return null
+            const state = store.getState()
+            const wId = state.activeWorktreeId
+            if (!wId) return null
+            return (state.tabsByWorktree[wId] ?? [])[0]?.id ?? null
+          })()
+          if (!tabId) return null
+          const manager = window.__paneManagers?.get(tabId)
+          if (!manager) return null
+          const panes = manager.getPanes() ?? []
+          const pane = panes.find((p: { id: number }) => p.id === paneId)
+          if (!pane) return null
+          return {
+            viewportY: pane.terminal.buffer.active.viewportY,
+            baseY: pane.terminal.buffer.active.baseY
+          }
+        },
+        { paneId: scrollBefore!.paneId }
+      )
+      if (scrollAfterWheel) {
+        const wheelJump = Math.abs(scrollAfterWheel.viewportY - scrollAfter!.viewportY)
+        const ratioAfterWheel =
+          scrollAfterWheel.baseY > 0 ? scrollAfterWheel.viewportY / scrollAfterWheel.baseY : 0
+        console.log(
+          '[scroll-test] post-wheel:',
+          JSON.stringify({
+            viewportYAfterDrag: scrollAfter!.viewportY,
+            viewportYAfterWheel: scrollAfterWheel.viewportY,
+            wheelJump,
+            ratioAfterWheel: ratioAfterWheel.toFixed(4)
+          })
+        )
+        // A small wheel scroll should move by a few lines, not jump hundreds
+        expect(wheelJump).toBeLessThan(scrollAfterWheel.baseY * 0.05)
+      }
+    }
+  })
+
+  test('@headful scroll position preserved in triple split layout', async ({ orcaPage }) => {
+    // Reproduce user's exact layout: triple split (top-left has content,
+    // bottom-left and right are empty)
+    await splitActiveTerminalPane(orcaPage, 'vertical') // left | right
+    await waitForPaneCount(orcaPage, 2)
+    await splitActiveTerminalPane(orcaPage, 'horizontal') // top-left / bottom-left | right
+    await waitForPaneCount(orcaPage, 3)
+
+    // Focus the first pane (top-left) and fill with wrapping content
+    const ptyId = await discoverActivePtyId(orcaPage)
+    await execInTerminal(
+      orcaPage,
+      ptyId,
+      'python3 -c "import string; s=string.ascii_letters+string.digits; [print(f\'LINE_{i:04d} \' + (s*8)[:500]) for i in range(1000)]"'
+    )
+    await waitForTerminalOutput(orcaPage, 'LINE_0999', 15_000)
+    await orcaPage.waitForTimeout(500)
+
+    const scrollBefore = await orcaPage.evaluate(() => {
+      const tabId = (() => {
+        const store = window.__store
+        if (!store) return null
+        const state = store.getState()
+        const wId = state.activeWorktreeId
+        if (!wId) return null
+        return (state.tabsByWorktree[wId] ?? [])[0]?.id ?? null
+      })()
+      if (!tabId) return null
+      const manager = window.__paneManagers?.get(tabId)
+      if (!manager) return null
+      const pane = manager.getActivePane()
+      if (!pane) return null
+      const buf = pane.terminal.buffer.active
+      const targetLine = Math.floor(buf.baseY / 2)
+      pane.terminal.scrollToLine(targetLine)
+      return {
+        viewportY: pane.terminal.buffer.active.viewportY,
+        baseY: buf.baseY,
+        paneId: pane.id,
+        cols: pane.terminal.cols
+      }
+    })
+    expect(scrollBefore).not.toBeNull()
+    expect(scrollBefore!.viewportY).toBeGreaterThan(0)
+
+    const consoleLogs: string[] = []
+    orcaPage.on('console', (msg) => {
+      const text = msg.text()
+      if (text.includes('[restoreScrollState]') || text.includes('[scrollToLineSync]')) {
+        consoleLogs.push(text)
+      }
+    })
+
+    // Drag the HORIZONTAL divider (between top-left and bottom-left) UP
+    // to change the height of the content pane — this changes rows and
+    // triggers reflow in a triple-split layout.
+    // Also try the vertical divider to change cols.
+    const divider = orcaPage.locator('.pane-divider.is-vertical').first()
+    await expect(divider).toBeVisible({ timeout: 3_000 })
+    const box = await divider.boundingBox()
+    expect(box).not.toBeNull()
+    const startX = box!.x + box!.width / 2
+    const startY = box!.y + box!.height / 2
+    await orcaPage.mouse.move(startX, startY)
+    await orcaPage.mouse.down()
+    // Drag RIGHT to widen left panes (more cols, less wrapping)
+    await orcaPage.mouse.move(startX + 200, startY, { steps: 30 })
+    await orcaPage.mouse.up()
+    await orcaPage.waitForTimeout(500)
+
+    const scrollAfter = await orcaPage.evaluate(
+      ({ paneId }) => {
+        const tabId = (() => {
+          const store = window.__store
+          if (!store) return null
+          const state = store.getState()
+          const wId = state.activeWorktreeId
+          if (!wId) return null
+          return (state.tabsByWorktree[wId] ?? [])[0]?.id ?? null
+        })()
+        if (!tabId) return null
+        const manager = window.__paneManagers?.get(tabId)
+        if (!manager) return null
+        const panes = manager.getPanes() ?? []
+        const pane = panes.find((p: { id: number }) => p.id === paneId)
+        if (!pane) return null
+        return {
+          viewportY: pane.terminal.buffer.active.viewportY,
+          baseY: pane.terminal.buffer.active.baseY,
+          cols: pane.terminal.cols
+        }
+      },
+      { paneId: scrollBefore!.paneId }
+    )
+    expect(scrollAfter).not.toBeNull()
+
+    const ratioBefore = scrollBefore!.viewportY / scrollBefore!.baseY
+    const ratioAfter = scrollAfter!.baseY > 0 ? scrollAfter!.viewportY / scrollAfter!.baseY : 0
+    const proportionalDrift = Math.abs(ratioAfter - ratioBefore)
+    console.log(
+      '[scroll-test] triple-split:',
+      JSON.stringify({
+        before: scrollBefore!.viewportY,
+        after: scrollAfter!.viewportY,
+        ratioBefore: ratioBefore.toFixed(4),
+        ratioAfter: ratioAfter.toFixed(4),
+        proportionalDrift: proportionalDrift.toFixed(4),
+        baseYBefore: scrollBefore!.baseY,
+        baseYAfter: scrollAfter!.baseY,
+        colsBefore: scrollBefore!.cols,
+        colsAfter: scrollAfter!.cols
+      })
+    )
+
+    // Check for Scrollable desync via mouse wheel
+    const paneEl = orcaPage.locator(`.pane[data-pane-id="${scrollBefore!.paneId}"]`).first()
+    const paneBox = await paneEl.boundingBox()
+    if (paneBox) {
+      await orcaPage.mouse.move(paneBox.x + paneBox.width / 2, paneBox.y + paneBox.height / 2)
+      await orcaPage.mouse.wheel(0, 50)
+      await orcaPage.waitForTimeout(200)
+
+      const scrollAfterWheel = await orcaPage.evaluate(
+        ({ paneId }) => {
+          const tabId = (() => {
+            const store = window.__store
+            if (!store) return null
+            const state = store.getState()
+            const wId = state.activeWorktreeId
+            if (!wId) return null
+            return (state.tabsByWorktree[wId] ?? [])[0]?.id ?? null
+          })()
+          if (!tabId) return null
+          const manager = window.__paneManagers?.get(tabId)
+          if (!manager) return null
+          const panes = manager.getPanes() ?? []
+          const pane = panes.find((p: { id: number }) => p.id === paneId)
+          if (!pane) return null
+          return {
+            viewportY: pane.terminal.buffer.active.viewportY,
+            baseY: pane.terminal.buffer.active.baseY
+          }
+        },
+        { paneId: scrollBefore!.paneId }
+      )
+      if (scrollAfterWheel) {
+        const wheelJump = Math.abs(scrollAfterWheel.viewportY - scrollAfter!.viewportY)
+        console.log(
+          '[scroll-test] triple-split-post-wheel:',
+          JSON.stringify({
+            viewportYAfterDrag: scrollAfter!.viewportY,
+            viewportYAfterWheel: scrollAfterWheel.viewportY,
+            wheelJump
+          })
+        )
+        expect(wheelJump).toBeLessThan(scrollAfterWheel.baseY * 0.05)
+      }
+    }
+
+    expect(proportionalDrift).toBeLessThanOrEqual(0.05)
+    expect(scrollAfter!.viewportY).toBeGreaterThan(scrollAfter!.baseY * 0.1)
+  })
+
+  test('@headful scroll position preserved during drag with active terminal writes', async ({
+    orcaPage
+  }) => {
+    await splitActiveTerminalPane(orcaPage, 'vertical')
+    await waitForPaneCount(orcaPage, 2)
+
+    const ptyId = await discoverActivePtyId(orcaPage)
+    await execInTerminal(orcaPage, ptyId, 'seq 1 5000')
+    await waitForTerminalOutput(orcaPage, '5000')
+    await orcaPage.waitForTimeout(300)
+
+    const scrollBefore = await orcaPage.evaluate(() => {
+      const tabId = (() => {
+        const store = window.__store
+        if (!store) return null
+        const state = store.getState()
+        const wId = state.activeWorktreeId
+        if (!wId) return null
+        return (state.tabsByWorktree[wId] ?? [])[0]?.id ?? null
+      })()
+      if (!tabId) return null
+      const manager = window.__paneManagers?.get(tabId)
+      if (!manager) return null
+      const pane = manager.getActivePane()
+      if (!pane) return null
+      const buf = pane.terminal.buffer.active
+      const targetLine = Math.floor(buf.baseY / 2)
+      pane.terminal.scrollToLine(targetLine)
+      return {
+        viewportY: pane.terminal.buffer.active.viewportY,
+        baseY: buf.baseY,
+        paneId: pane.id,
+        cols: pane.terminal.cols
+      }
+    })
+    expect(scrollBefore).not.toBeNull()
+    expect(scrollBefore!.viewportY).toBeGreaterThan(0)
+
+    // Start a background loop that writes to the terminal during drag,
+    // simulating what Claude Code does when it redraws on SIGWINCH
+    await execInTerminal(
+      orcaPage,
+      ptyId,
+      'while true; do echo "REDRAW $(date +%s%N)"; sleep 0.05; done &'
+    )
+    await orcaPage.waitForTimeout(200)
+    // Re-scroll after the writes started (they push to bottom)
+    await orcaPage.evaluate(
+      ({ paneId, targetViewportY }) => {
+        const tabId = (() => {
+          const store = window.__store
+          if (!store) return null
+          const state = store.getState()
+          const wId = state.activeWorktreeId
+          if (!wId) return null
+          return (state.tabsByWorktree[wId] ?? [])[0]?.id ?? null
+        })()
+        if (!tabId) return
+        const manager = window.__paneManagers?.get(tabId)
+        if (!manager) return
+        const panes = manager.getPanes() ?? []
+        const pane = panes.find((p: { id: number }) => p.id === paneId)
+        if (!pane) return
+        pane.terminal.scrollToLine(targetViewportY)
+      },
+      { paneId: scrollBefore!.paneId, targetViewportY: scrollBefore!.viewportY }
+    )
+    await orcaPage.waitForTimeout(100)
+
+    const divider = orcaPage.locator('.pane-divider.is-vertical').first()
+    await expect(divider).toBeVisible({ timeout: 3_000 })
+    const box = await divider.boundingBox()
+    expect(box).not.toBeNull()
+    const startX = box!.x + box!.width / 2
+    const startY = box!.y + box!.height / 2
+    await orcaPage.mouse.move(startX, startY)
+    await orcaPage.mouse.down()
+    await orcaPage.mouse.move(startX + 100, startY, { steps: 15 })
+    await orcaPage.mouse.up()
+
+    // Kill the background writer
+    await execInTerminal(orcaPage, ptyId, 'kill %1 2>/dev/null; true')
+    await orcaPage.waitForTimeout(500)
+
+    const scrollAfter = await orcaPage.evaluate(
+      ({ paneId }) => {
+        const tabId = (() => {
+          const store = window.__store
+          if (!store) return null
+          const state = store.getState()
+          const wId = state.activeWorktreeId
+          if (!wId) return null
+          return (state.tabsByWorktree[wId] ?? [])[0]?.id ?? null
+        })()
+        if (!tabId) return null
+        const manager = window.__paneManagers?.get(tabId)
+        if (!manager) return null
+        const panes = manager.getPanes() ?? []
+        const pane = panes.find((p: { id: number }) => p.id === paneId)
+        if (!pane) return null
+        return {
+          viewportY: pane.terminal.buffer.active.viewportY,
+          baseY: pane.terminal.buffer.active.baseY,
+          cols: pane.terminal.cols
+        }
+      },
+      { paneId: scrollBefore!.paneId }
+    )
+    expect(scrollAfter).not.toBeNull()
+    const drift = Math.abs(scrollAfter!.viewportY - scrollBefore!.viewportY)
+    console.log('[scroll-test] active-writes:', {
+      before: scrollBefore!.viewportY,
+      after: scrollAfter!.viewportY,
+      drift,
+      baseYBefore: scrollBefore!.baseY,
+      baseYAfter: scrollAfter!.baseY,
+      colsBefore: scrollBefore!.cols,
+      colsAfter: scrollAfter!.cols
+    })
+    // With active writes, allow more tolerance but must not jump to top
+    const maxDrift = scrollBefore!.baseY * 0.1
+    expect(drift).toBeLessThanOrEqual(maxDrift)
+    expect(scrollAfter!.viewportY).toBeGreaterThan(scrollBefore!.baseY * 0.1)
+  })
+
+  test('@headful scroll position preserved during drag with TUI-style redraws', async ({
+    orcaPage
+  }) => {
+    await splitActiveTerminalPane(orcaPage, 'vertical')
+    await waitForPaneCount(orcaPage, 2)
+
+    const ptyId = await discoverActivePtyId(orcaPage)
+    await execInTerminal(orcaPage, ptyId, 'seq 1 5000')
+    await waitForTerminalOutput(orcaPage, '5000')
+    await orcaPage.waitForTimeout(300)
+
+    const scrollBefore = await orcaPage.evaluate(() => {
+      const tabId = (() => {
+        const store = window.__store
+        if (!store) return null
+        const state = store.getState()
+        const wId = state.activeWorktreeId
+        if (!wId) return null
+        return (state.tabsByWorktree[wId] ?? [])[0]?.id ?? null
+      })()
+      if (!tabId) return null
+      const manager = window.__paneManagers?.get(tabId)
+      if (!manager) return null
+      const pane = manager.getActivePane()
+      if (!pane) return null
+      const buf = pane.terminal.buffer.active
+      const targetLine = Math.floor(buf.baseY / 2)
+      pane.terminal.scrollToLine(targetLine)
+      return {
+        viewportY: pane.terminal.buffer.active.viewportY,
+        baseY: buf.baseY,
+        paneId: pane.id,
+        cols: pane.terminal.cols
+      }
+    })
+    expect(scrollBefore).not.toBeNull()
+    expect(scrollBefore!.viewportY).toBeGreaterThan(0)
+
+    // Simulate TUI redraw: a SIGWINCH-responsive script that clears the
+    // last few lines and rewrites them — like Claude Code's status bar.
+    // This uses cursor movement + clear-to-end escape sequences.
+    await execInTerminal(
+      orcaPage,
+      ptyId,
+      String.raw`trap 'printf "\033[s\033[999;1H\033[2K--- RESIZE %dx%d ---\033[u" $COLUMNS $LINES' WINCH; while true; do sleep 0.1; done &`
+    )
+    await orcaPage.waitForTimeout(200)
+    // Re-scroll after trap setup
+    await orcaPage.evaluate(
+      ({ paneId, targetViewportY }) => {
+        const tabId = (() => {
+          const store = window.__store
+          if (!store) return null
+          const state = store.getState()
+          const wId = state.activeWorktreeId
+          if (!wId) return null
+          return (state.tabsByWorktree[wId] ?? [])[0]?.id ?? null
+        })()
+        if (!tabId) return
+        const manager = window.__paneManagers?.get(tabId)
+        if (!manager) return
+        const panes = manager.getPanes() ?? []
+        const pane = panes.find((p: { id: number }) => p.id === paneId)
+        if (!pane) return
+        pane.terminal.scrollToLine(targetViewportY)
+      },
+      { paneId: scrollBefore!.paneId, targetViewportY: scrollBefore!.viewportY }
+    )
+    await orcaPage.waitForTimeout(100)
+
+    const divider = orcaPage.locator('.pane-divider.is-vertical').first()
+    await expect(divider).toBeVisible({ timeout: 3_000 })
+    const box = await divider.boundingBox()
+    expect(box).not.toBeNull()
+    const startX = box!.x + box!.width / 2
+    const startY = box!.y + box!.height / 2
+    await orcaPage.mouse.move(startX, startY)
+    await orcaPage.mouse.down()
+    // Slower drag with more steps to trigger multiple SIGWINCHes
+    await orcaPage.mouse.move(startX + 150, startY, { steps: 30 })
+    await orcaPage.mouse.up()
+
+    await execInTerminal(orcaPage, ptyId, 'kill %1 2>/dev/null; true')
+    await orcaPage.waitForTimeout(500)
+
+    const scrollAfter = await orcaPage.evaluate(
+      ({ paneId }) => {
+        const tabId = (() => {
+          const store = window.__store
+          if (!store) return null
+          const state = store.getState()
+          const wId = state.activeWorktreeId
+          if (!wId) return null
+          return (state.tabsByWorktree[wId] ?? [])[0]?.id ?? null
+        })()
+        if (!tabId) return null
+        const manager = window.__paneManagers?.get(tabId)
+        if (!manager) return null
+        const panes = manager.getPanes() ?? []
+        const pane = panes.find((p: { id: number }) => p.id === paneId)
+        if (!pane) return null
+        return {
+          viewportY: pane.terminal.buffer.active.viewportY,
+          baseY: pane.terminal.buffer.active.baseY,
+          cols: pane.terminal.cols
+        }
+      },
+      { paneId: scrollBefore!.paneId }
+    )
+    expect(scrollAfter).not.toBeNull()
+    const drift = Math.abs(scrollAfter!.viewportY - scrollBefore!.viewportY)
+    console.log('[scroll-test] tui-redraw:', {
+      before: scrollBefore!.viewportY,
+      after: scrollAfter!.viewportY,
+      drift,
+      baseYBefore: scrollBefore!.baseY,
+      baseYAfter: scrollAfter!.baseY,
+      colsBefore: scrollBefore!.cols,
+      colsAfter: scrollAfter!.cols
+    })
+    const maxDrift = scrollBefore!.baseY * 0.1
+    expect(drift).toBeLessThanOrEqual(maxDrift)
+    expect(scrollAfter!.viewportY).toBeGreaterThan(scrollBefore!.baseY * 0.1)
+  })
+
+  /**
+   * Regression test for the SIGWINCH scroll corruption bug.
+   *
+   * Uses an Ink-like TUI simulator that reproduces the exact rendering
+   * pattern that caused Claude Code sessions to lose scroll position during
+   * divider drag resize: cursor-up + clear-to-end-of-display + rewrite.
+   *
+   * The bug: drag resize → PTY resize → SIGWINCH → TUI redraws → viewportY
+   * corrupted → ResizeObserver captures corrupted state → scroll jumps to 0.
+   *
+   * Why headful: pointer capture requires a real pointer ID from a visible window.
+   */
+  test('@headful scroll position preserved during drag with Ink-style TUI redraws', async ({
+    orcaPage
+  }) => {
+    await splitActiveTerminalPane(orcaPage, 'vertical')
+    await waitForPaneCount(orcaPage, 2)
+
+    const ptyId = await discoverActivePtyId(orcaPage)
+
+    // Generate scrollback content with long wrapping lines
+    await execInTerminal(
+      orcaPage,
+      ptyId,
+      [
+        'python3 -c "',
+        'import string, sys',
+        'chars = string.ascii_letters + string.digits',
+        'for i in range(300):',
+        "    line = f\\'LINE{i:04d} \\' + (chars * 3)[:200]",
+        '    print(line)',
+        'sys.stdout.flush()',
+        '"'
+      ].join('\n')
+    )
+    await waitForTerminalOutput(orcaPage, 'LINE0299', 15_000)
+    await orcaPage.waitForTimeout(500)
+
+    // Start the Ink TUI simulator (redraws on SIGWINCH like Claude Code)
+    const fixturePath = path.resolve('tests/e2e/fixtures/ink-tui-sim.mjs')
+    await execInTerminal(orcaPage, ptyId, `node ${fixturePath} &`)
+    await orcaPage.waitForTimeout(1000)
+
+    // Scroll to ~middle of scrollback
+    const scrollBefore = await orcaPage.evaluate(() => {
+      const store = window.__store
+      if (!store) {
+        return null
+      }
+      const state = store.getState()
+      const wId = state.activeWorktreeId
+      if (!wId) {
+        return null
+      }
+      const tabId = (state.tabsByWorktree[wId] ?? [])[0]?.id ?? null
+      if (!tabId) {
+        return null
+      }
+      const manager = window.__paneManagers?.get(tabId)
+      if (!manager) {
+        return null
+      }
+      const pane = manager.getActivePane()
+      if (!pane) {
+        return null
+      }
+      const buf = pane.terminal.buffer.active
+      const targetLine = Math.floor(buf.baseY / 2)
+      pane.terminal.scrollToLine(targetLine)
+      return {
+        viewportY: pane.terminal.buffer.active.viewportY,
+        baseY: buf.baseY,
+        paneId: pane.id,
+        cols: pane.terminal.cols
+      }
+    })
+    expect(scrollBefore).not.toBeNull()
+    expect(scrollBefore!.viewportY).toBeGreaterThan(0)
+    await orcaPage.waitForTimeout(200)
+
+    // Drag the divider — each step triggers fit() → onResize. The PTY resize
+    // is suppressed during drag but flushed at drag end, sending SIGWINCH to
+    // the Ink TUI simulator which does cursor-up + clear + rewrite.
+    const divider = orcaPage.locator('.pane-divider.is-vertical').first()
+    await expect(divider).toBeVisible({ timeout: 3_000 })
+    const box = await divider.boundingBox()
+    expect(box).not.toBeNull()
+    const startX = box!.x + box!.width / 2
+    const startY = box!.y + box!.height / 2
+    await orcaPage.mouse.move(startX, startY)
+    await orcaPage.mouse.down()
+    await orcaPage.mouse.move(startX + 150, startY, { steps: 20 })
+    await orcaPage.mouse.up()
+
+    // Wait for the SIGWINCH settling period (500ms) + buffer
+    await orcaPage.waitForTimeout(1000)
+
+    const scrollAfter = await orcaPage.evaluate(
+      ({ paneId }) => {
+        const store = window.__store
+        if (!store) {
+          return null
+        }
+        const state = store.getState()
+        const wId = state.activeWorktreeId
+        if (!wId) {
+          return null
+        }
+        const tabId = (state.tabsByWorktree[wId] ?? [])[0]?.id ?? null
+        if (!tabId) {
+          return null
+        }
+        const manager = window.__paneManagers?.get(tabId)
+        if (!manager) {
+          return null
+        }
+        const panes = manager.getPanes() ?? []
+        const pane = panes.find((p: { id: number }) => p.id === paneId)
+        if (!pane) {
+          return null
+        }
+        return {
+          viewportY: pane.terminal.buffer.active.viewportY,
+          baseY: pane.terminal.buffer.active.baseY,
+          cols: pane.terminal.cols
+        }
+      },
+      { paneId: scrollBefore!.paneId }
+    )
+    expect(scrollAfter).not.toBeNull()
+
+    // Kill the background TUI simulator
+    await execInTerminal(orcaPage, ptyId, 'kill %1 2>/dev/null; true')
+    await orcaPage.waitForTimeout(300)
+
+    const ratioBefore = scrollBefore!.viewportY / scrollBefore!.baseY
+    const ratioAfter = scrollAfter!.baseY > 0 ? scrollAfter!.viewportY / scrollAfter!.baseY : 0
+    const proportionalDrift = Math.abs(ratioAfter - ratioBefore)
+    console.log(
+      '[scroll-test] ink-tui-sim:',
+      JSON.stringify({
+        before: scrollBefore!.viewportY,
+        after: scrollAfter!.viewportY,
+        ratioBefore: ratioBefore.toFixed(4),
+        ratioAfter: ratioAfter.toFixed(4),
+        proportionalDrift: proportionalDrift.toFixed(4),
+        baseYBefore: scrollBefore!.baseY,
+        baseYAfter: scrollAfter!.baseY,
+        colsBefore: scrollBefore!.cols,
+        colsAfter: scrollAfter!.cols
+      })
+    )
+
+    expect(proportionalDrift).toBeLessThanOrEqual(0.05)
+    expect(scrollAfter!.viewportY).toBeGreaterThan(scrollAfter!.baseY * 0.1)
+  })
+
   /**
    * User Prompt:
    * - closing panes works