fix(desktop): restore native window dragging (#770 #796)

Remove the Windows renderer-side drag delta fallback and keep frameless window movement on Electron app-region handling. Reject drag movement payloads on the legacy IPC channel so window drags cannot mutate bounds through repeated setPosition calls.

Tested: cd desktop && bun run test --run src/hooks/useElectronWindowDragRegions.test.tsx electron/ipc/capabilities.test.ts src/lib/desktopHost/electronHost.test.ts
Tested: bun run check:desktop
Tested: bun run check:native
Confidence: high
Scope-risk: narrow

desktop/electron/ipc/capabilities.test.ts

@@ -26,9 +26,7 @@ describe('Electron IPC capabilities', () => {
     expect(validateElectronIpcPayload(ELECTRON_IPC_CHANNELS.windowClose, undefined)).toBe(true)
     expect(validateElectronIpcPayload(ELECTRON_IPC_CHANNELS.windowClose, {})).toBe(false)
     expect(validateElectronIpcPayload(ELECTRON_IPC_CHANNELS.windowStartDragging, undefined)).toBe(true)
-    expect(validateElectronIpcPayload(ELECTRON_IPC_CHANNELS.windowStartDragging, { deltaX: 4, deltaY: -2 })).toBe(true)
-    expect(validateElectronIpcPayload(ELECTRON_IPC_CHANNELS.windowStartDragging, { deltaX: 4, deltaY: Number.NaN })).toBe(false)
-    expect(validateElectronIpcPayload(ELECTRON_IPC_CHANNELS.windowStartDragging, { deltaX: 4, deltaY: -2, extra: true })).toBe(false)
+    expect(validateElectronIpcPayload(ELECTRON_IPC_CHANNELS.windowStartDragging, { deltaX: 4, deltaY: -2 })).toBe(false)
     expect(validateElectronIpcPayload(ELECTRON_IPC_CHANNELS.terminalWrite, { sessionId: 1, data: 'pwd\n' })).toBe(true)
     expect(validateElectronIpcPayload(ELECTRON_IPC_CHANNELS.terminalWrite, { sessionId: '1', data: 'pwd\n' })).toBe(false)
     expect(validateElectronIpcPayload(ELECTRON_IPC_CHANNELS.terminalSpawn, { cols: 80, rows: 24, cwd: '/tmp' })).toBe(true)

desktop/electron/ipc/capabilities.ts

@@ -56,17 +56,6 @@ const boundsPayload: Validator = value =>
   && typeof value.width === 'number'
   && typeof value.height === 'number'
 
-const windowDragMovePayload: Validator = value =>
-  value === undefined
-  || (
-    isRecord(value)
-    && hasOnlyKeys(value, ['deltaX', 'deltaY'])
-    && typeof value.deltaX === 'number'
-    && Number.isFinite(value.deltaX)
-    && typeof value.deltaY === 'number'
-    && Number.isFinite(value.deltaY)
-  )
-
 const urlWithOptionalBounds: Validator = value =>
   isRecord(value)
   && typeof value.url === 'string'
@@ -102,7 +91,7 @@ export const ELECTRON_IPC_VALIDATORS = {
   [ELECTRON_IPC_CHANNELS.windowMinimize]: noPayload,
   [ELECTRON_IPC_CHANNELS.windowToggleMaximize]: noPayload,
   [ELECTRON_IPC_CHANNELS.windowClose]: noPayload,
-  [ELECTRON_IPC_CHANNELS.windowStartDragging]: windowDragMovePayload,
+  [ELECTRON_IPC_CHANNELS.windowStartDragging]: noPayload,
   [ELECTRON_IPC_CHANNELS.windowRequestAttention]: noPayload,
   [ELECTRON_IPC_CHANNELS.windowFocus]: noPayload,
   [ELECTRON_IPC_CHANNELS.windowIsMaximized]: noPayload,

desktop/electron/main.ts

@@ -297,19 +297,7 @@ function registerIpcHandlers() {
     else window.maximize()
   })
   registerHandler(ELECTRON_IPC_CHANNELS.windowClose, event => currentWindow(event).close())
-  registerHandler(ELECTRON_IPC_CHANNELS.windowStartDragging, (event, payload) => {
-    if (!payload || typeof payload !== 'object') return undefined
-    const { deltaX, deltaY } = payload as { deltaX?: number, deltaY?: number }
-    if (!Number.isFinite(deltaX) || !Number.isFinite(deltaY)) return undefined
-    const window = currentWindow(event)
-    if (window.isMaximized()) window.unmaximize()
-    const bounds = window.getBounds()
-    window.setPosition(
-      Math.round(bounds.x + deltaX!),
-      Math.round(bounds.y + deltaY!),
-    )
-    return undefined
-  })
+  registerHandler(ELECTRON_IPC_CHANNELS.windowStartDragging, () => undefined)
   registerHandler(ELECTRON_IPC_CHANNELS.windowRequestAttention, event => currentWindow(event).flashFrame(true))
   registerHandler(ELECTRON_IPC_CHANNELS.windowFocus, event => currentWindow(event).focus())
   registerHandler(ELECTRON_IPC_CHANNELS.windowIsMaximized, event => currentWindow(event).isMaximized())

desktop/src/hooks/useElectronWindowDragRegions.test.tsx

@@ -56,15 +56,15 @@ describe('useElectronWindowDragRegions', () => {
     delete document.documentElement.dataset.desktopDragMode
   })
 
-  it('uses the manual drag fallback on Windows only', () => {
-    expect(shouldUseManualWindowDrag('Win32')).toBe(true)
+  it('uses native app-region dragging on every platform', () => {
+    expect(shouldUseManualWindowDrag('Win32')).toBe(false)
     expect(shouldUseManualWindowDrag('MacIntel')).toBe(false)
     expect(shouldUseManualWindowDrag('Linux x86_64')).toBe(false)
   })
 
-  it('moves the native window while dragging a desktop drag region', async () => {
+  it('leaves Windows drag regions on the native app-region path', async () => {
     render(<Harness />)
-    expect(document.documentElement.dataset.desktopDragMode).toBe('manual')
+    expect(document.documentElement.dataset.desktopDragMode).toBeUndefined()
 
     fireEvent.mouseDown(screen.getByTestId('blank-space'), {
       button: 0,
@@ -77,10 +77,7 @@ describe('useElectronWindowDragRegions', () => {
     })
 
     await waitFor(() => {
-      expect(desktopHostMock.host.window.startDragging).toHaveBeenCalledWith({
-        deltaX: 30,
-        deltaY: 30,
-      })
+      expect(desktopHostMock.host.window.startDragging).not.toHaveBeenCalled()
     })
 
     fireEvent.mouseUp(window)
@@ -89,10 +86,10 @@ describe('useElectronWindowDragRegions', () => {
       screenY: 210,
     })
 
-    expect(desktopHostMock.host.window.startDragging).toHaveBeenCalledTimes(1)
+    expect(desktopHostMock.host.window.startDragging).not.toHaveBeenCalled()
   })
 
-  it('keeps buttons and tab reorder targets out of the window drag fallback', () => {
+  it('does not route buttons or tab reorder targets through legacy drag IPC', () => {
     render(<Harness />)
 
     fireEvent.mouseDown(screen.getByRole('button', { name: 'Button' }), {

desktop/src/hooks/useElectronWindowDragRegions.ts

@@ -1,86 +1,9 @@
-import { useEffect } from 'react'
-import { getDesktopHost } from '../lib/desktopHost'
-
-const DRAG_REGION_SELECTOR = '[data-desktop-drag-region]'
-const MANUAL_DRAG_MODE = 'manual'
-const NO_DRAG_SELECTOR = [
-  '[data-desktop-no-drag-region]',
-  'button',
-  'input',
-  'textarea',
-  'select',
-  'a',
-  '[role="button"]',
-  '[draggable="true"]',
-  '.tab-bar-interactive',
-  '.tab-bar-interactive *',
-].join(',')
-
 export function shouldUseManualWindowDrag(platform = typeof navigator === 'undefined' ? '' : navigator.platform) {
-  return /Win/i.test(platform)
-}
-
-export function isDesktopDragStartTarget(target: EventTarget | null): target is Element {
-  if (!(target instanceof Element)) return false
-  if (target.closest(NO_DRAG_SELECTOR)) return false
-  return Boolean(target.closest(DRAG_REGION_SELECTOR))
+  void platform
+  return false
 }
 
 export function useElectronWindowDragRegions() {
-  useEffect(() => {
-    const host = getDesktopHost()
-    if (!host.isDesktop || !host.capabilities?.windowControls || !host.window?.startDragging) return
-    if (!shouldUseManualWindowDrag()) return
-
-    const previousDragMode = document.documentElement.dataset.desktopDragMode
-    document.documentElement.dataset.desktopDragMode = MANUAL_DRAG_MODE
-
-    let dragging = false
-    let lastScreenX = 0
-    let lastScreenY = 0
-
-    const stopDragging = () => {
-      dragging = false
-    }
-
-    const handleMouseDown = (event: MouseEvent) => {
-      if (event.button !== 0) return
-      if (!isDesktopDragStartTarget(event.target)) return
-      dragging = true
-      lastScreenX = event.screenX
-      lastScreenY = event.screenY
-      event.preventDefault()
-    }
-
-    const handleMouseMove = (event: MouseEvent) => {
-      if (!dragging) return
-      const deltaX = event.screenX - lastScreenX
-      const deltaY = event.screenY - lastScreenY
-      if (deltaX === 0 && deltaY === 0) return
-
-      lastScreenX = event.screenX
-      lastScreenY = event.screenY
-      void host.window.startDragging({ deltaX, deltaY }).catch(error => {
-        console.error('Window drag fallback failed', error)
-        stopDragging()
-      })
-    }
-
-    document.addEventListener('mousedown', handleMouseDown, true)
-    window.addEventListener('mousemove', handleMouseMove, true)
-    window.addEventListener('mouseup', stopDragging, true)
-    window.addEventListener('blur', stopDragging)
-
-    return () => {
-      if (previousDragMode === undefined) {
-        delete document.documentElement.dataset.desktopDragMode
-      } else {
-        document.documentElement.dataset.desktopDragMode = previousDragMode
-      }
-      document.removeEventListener('mousedown', handleMouseDown, true)
-      window.removeEventListener('mousemove', handleMouseMove, true)
-      window.removeEventListener('mouseup', stopDragging, true)
-      window.removeEventListener('blur', stopDragging)
-    }
-  }, [])
+  // Electron's native app-region dragging is the supported frameless-window path.
+  // The previous Windows JS delta fallback could resize frameless windows while moving them.
 }

desktop/src/lib/desktopHost/electronHost.test.ts

@@ -45,19 +45,16 @@ describe('electron desktop host', () => {
     expect(host.capabilities.windowControls).toBe(true)
   })
 
-  it('forwards drag-region fallback movement through the window dragging IPC channel', async () => {
+  it('keeps the legacy window dragging IPC channel payload-free', async () => {
     const invoke = vi.fn().mockResolvedValue(undefined)
     const host = createElectronHost({
       invoke,
       subscribe: vi.fn(),
     })
 
-    await host.window.startDragging({ deltaX: 12, deltaY: -8 })
+    await host.window.startDragging()
 
-    expect(invoke).toHaveBeenCalledWith(ELECTRON_IPC_CHANNELS.windowStartDragging, {
-      deltaX: 12,
-      deltaY: -8,
-    })
+    expect(invoke).toHaveBeenCalledWith(ELECTRON_IPC_CHANNELS.windowStartDragging, undefined)
   })
 
   it('opens dedicated trace windows through a narrow IPC channel', async () => {

desktop/src/lib/desktopHost/electronHost.ts

@@ -118,7 +118,7 @@ export function createElectronHost(bridge: ElectronHostBridge): DesktopHost {
       minimize: () => invoke(ELECTRON_IPC_CHANNELS.windowMinimize),
       toggleMaximize: () => invoke(ELECTRON_IPC_CHANNELS.windowToggleMaximize),
       close: () => invoke(ELECTRON_IPC_CHANNELS.windowClose),
-      startDragging: input => invoke(ELECTRON_IPC_CHANNELS.windowStartDragging, input),
+      startDragging: () => invoke(ELECTRON_IPC_CHANNELS.windowStartDragging),
       requestAttention: () => invoke(ELECTRON_IPC_CHANNELS.windowRequestAttention),
       focus: () => invoke(ELECTRON_IPC_CHANNELS.windowFocus),
       isMaximized: () => invoke(ELECTRON_IPC_CHANNELS.windowIsMaximized),

desktop/src/lib/desktopHost/types.ts

@@ -130,11 +130,6 @@ export type PreviewHostMessage = PreviewCaptureMessage | PreviewPickerMessage
 
 export type AppModeConfig = SettingsAppModeConfig
 
-export type WindowDragMoveInput = {
-  deltaX: number
-  deltaY: number
-}
-
 export type AppModeSetInput = {
   mode: SettingsAppMode
   portableDir: string | null
@@ -192,7 +187,7 @@ export type DesktopHost = {
     minimize(): Promise<void>
     toggleMaximize(): Promise<void>
     close(): Promise<void>
-    startDragging(input?: WindowDragMoveInput): Promise<void>
+    startDragging(): Promise<void>
     requestAttention(): Promise<void>
     focus(): Promise<void>
     isMaximized(): Promise<boolean>

desktop/src/theme/globals.css

@@ -959,14 +959,10 @@ html, body, #root {
 }
 
 /* Desktop drag region */
-html:not([data-desktop-drag-mode="manual"]) [data-desktop-drag-region] {
+[data-desktop-drag-region] {
   app-region: drag;
   -webkit-app-region: drag;
 }
-html[data-desktop-drag-mode="manual"] [data-desktop-drag-region] {
-  app-region: no-drag;
-  -webkit-app-region: no-drag;
-}
 button, input, textarea, select, a, [role="button"] {
   app-region: no-drag;
   -webkit-app-region: no-drag;