feat(desktop): open any chat in its own window (#43219)

Pops a session into a standalone, focused window for side-by-side work.
A secondary window loads the renderer at the session route with a
?win=secondary flag (ahead of the HashRouter '#'); it drops the global
sidebar plus the install/onboarding overlays and renders a single chat,
sharing the one local gateway over WS (no backend duplication). The main
process keys windows by sessionId so re-opening focuses the existing one
and self-cleans on close.

Open it via:
- ⌘-click (mac) / ⌃-click (win/linux) a sidebar session — the universal
  "open in new window" gesture. Archive moves to the ⋯ / right-click menus
  only, off the easy-to-misfire modifier-click.
- "New window" in the session ⋯ and context menus (link-external icon,
  i18n'd across en/ja/zh/zh-hant).

A standalone window has no left rail, so AppShell treats its edge as
uncovered and applies the titlebar inset — the chat title clears the
macOS traffic lights instead of hiding behind them.

Co-authored-by: tim404x <tim404x@users.noreply.github.com>

apps/desktop/src/app/chat/sidebar/session-actions-menu.tsx

@@ -21,6 +21,7 @@ import { triggerHaptic } from '@/lib/haptics'
 import { exportSession } from '@/lib/session-export'
 import { notify, notifyError } from '@/store/notifications'
 import { setSessions } from '@/store/session'
+import { canOpenSessionWindow, openSessionInNewWindow } from '@/store/windows'
 
 interface SessionActions {
   sessionId: string
@@ -68,6 +69,19 @@ function useSessionActions({ sessionId, title, pinned = false, profile, onPin, o
         void writeClipboardText(sessionId).catch(err => notifyError(err, r.copyIdFailed))
       }
     },
+    ...(canOpenSessionWindow()
+      ? [
+          {
+            disabled: !sessionId,
+            icon: 'link-external',
+            label: r.newWindow,
+            onSelect: () => {
+              triggerHaptic('selection')
+              void openSessionInNewWindow(sessionId)
+            }
+          }
+        ]
+      : []),
     {
       disabled: !sessionId,
       icon: 'cloud-download',

apps/desktop/src/app/chat/sidebar/session-row.tsx

@@ -13,6 +13,7 @@ import { triggerHaptic } from '@/lib/haptics'
 import { handoffOriginSource, sessionSourceLabel } from '@/lib/session-source'
 import { cn } from '@/lib/utils'
 import { $attentionSessionIds } from '@/store/session'
+import { canOpenSessionWindow, openSessionInNewWindow } from '@/store/windows'
 
 import { SessionActionsMenu, SessionContextMenu } from './session-actions-menu'
 
@@ -132,11 +133,15 @@ export function SidebarSessionRow({
               return
             }
 
-            if (event.metaKey || event.ctrlKey) {
+            // ⌘-click (mac) / ⌃-click (win/linux) pops the chat into its own
+            // window — the universal "open in a new window" gesture. Archive
+            // lives in the row's ⋯ and right-click menus. Falls through to a
+            // normal resume when standalone windows aren't available (web embed).
+            if ((event.metaKey || event.ctrlKey) && canOpenSessionWindow()) {
               event.preventDefault()
               event.stopPropagation()
               triggerHaptic('selection')
-              onArchive()
+              void openSessionInNewWindow(session.id)
 
               return
             }

apps/desktop/src/app/desktop-controller.tsx

@@ -50,9 +50,9 @@ import {
   $currentCwd,
   $freshDraftReady,
   $gatewayState,
+  $messagingSessions,
   $selectedStoredSessionId,
   $sessions,
-  $messagingSessions,
   $workingSessionIds,
   CRON_SECTION_LIMIT,
   getRecentlySettledSessionIds,
@@ -76,6 +76,7 @@ import {
   setSessionsTotal
 } from '../store/session'
 import { openUpdatesWindow, startUpdatePoller, stopUpdatePoller } from '../store/updates'
+import { isSecondaryWindow } from '../store/windows'
 
 import { ChatView } from './chat'
 import { useComposerActions } from './chat/hooks/use-composer-actions'
@@ -791,19 +792,21 @@ export function DesktopController() {
 
   const overlays = (
     <>
-      <DesktopInstallOverlay />
+      {!isSecondaryWindow() && <DesktopInstallOverlay />}
       {/* One PTY-backed terminal mounted forever; <TerminalSlot /> placeholders
           decide where it shows. Toggling fullscreen never rebuilds the shell. */}
       <PersistentTerminal cwd={currentCwd} onAddSelectionToChat={composer.addTerminalSelectionAttachment} />
-      <DesktopOnboardingOverlay
-        enabled={gatewayState === 'open'}
-        onCompleted={() => {
-          void refreshHermesConfig()
-          void refreshCurrentModel()
-          void queryClient.invalidateQueries({ queryKey: ['model-options'] })
-        }}
-        requestGateway={requestGateway}
-      />
+      {!isSecondaryWindow() && (
+        <DesktopOnboardingOverlay
+          enabled={gatewayState === 'open'}
+          onCompleted={() => {
+            void refreshHermesConfig()
+            void refreshCurrentModel()
+            void queryClient.invalidateQueries({ queryKey: ['model-options'] })
+          }}
+          requestGateway={requestGateway}
+        />
+      )}
       <ModelPickerOverlay gateway={gatewayRef.current || undefined} onSelect={selectModel} />
       <ModelVisibilityOverlay gateway={gatewayRef.current || undefined} onOpenProviders={openProviderSettings} />
       <UpdatesOverlay />
@@ -957,20 +960,22 @@ export function DesktopController() {
       statusbarItems={statusbarItems}
       titlebarTools={titlebarToolGroups.flat.right}
     >
-      <Pane
-        disabled={terminalTakeoverActive}
-        forceCollapsed={narrowViewport}
-        hoverReveal
-        id="chat-sidebar"
-        maxWidth={SIDEBAR_MAX_WIDTH}
-        minWidth={SIDEBAR_DEFAULT_WIDTH}
-        onOverlayActiveChange={setSidebarOverlayMounted}
-        resizable
-        side={sidebarSide}
-        width={`${SIDEBAR_DEFAULT_WIDTH}px`}
-      >
-        {sidebar}
-      </Pane>
+      {!isSecondaryWindow() && (
+        <Pane
+          disabled={terminalTakeoverActive}
+          forceCollapsed={narrowViewport}
+          hoverReveal
+          id="chat-sidebar"
+          maxWidth={SIDEBAR_MAX_WIDTH}
+          minWidth={SIDEBAR_DEFAULT_WIDTH}
+          onOverlayActiveChange={setSidebarOverlayMounted}
+          resizable
+          side={sidebarSide}
+          width={`${SIDEBAR_DEFAULT_WIDTH}px`}
+        >
+          {sidebar}
+        </Pane>
+      )}
       <PaneMain>
         <Routes>
           <Route element={terminalTakeoverActive ? takeoverTerminalView : chatView} index />

apps/desktop/src/app/shell/app-shell.tsx

@@ -16,6 +16,7 @@ import {
 } from '@/store/layout'
 import { $paneWidthOverride } from '@/store/panes'
 import { $connection } from '@/store/session'
+import { isSecondaryWindow } from '@/store/windows'
 
 import { SIDEBAR_COLLAPSE_MEDIA_QUERY } from '../layout-constants'
 
@@ -77,8 +78,10 @@ export function AppShell({
   // window's left edge. Default layout: the sessions sidebar sits there.
   // Flipped layout: the file browser does instead. Below the collapse
   // breakpoint both rails are force-collapsed (hover-reveal overlay), so the
-  // edge is uncovered regardless of their stored open state.
-  const leftEdgePaneOpen = !narrowViewport && (panesFlipped ? fileBrowserOpen : sidebarOpen)
+  // edge is uncovered regardless of their stored open state. A standalone
+  // session window renders no sidebar at all, so its edge is always uncovered.
+  const leftEdgePaneOpen =
+    !narrowViewport && !isSecondaryWindow() && (panesFlipped ? fileBrowserOpen : sidebarOpen)
 
   const titlebarContentInset = leftEdgePaneOpen
     ? 0

apps/desktop/src/global.d.ts

@@ -18,6 +18,10 @@ declare global {
       // reaper spares it while its chat is active.
       touchBackend: (profile?: string | null) => Promise<{ ok: boolean }>
       getGatewayWsUrl: (profile?: null | string) => Promise<string>
+      // Open (or focus) a standalone OS window for a single chat session so
+      // the user can work with multiple chats side by side. Returns ok:false
+      // with an error code when the sessionId is empty/invalid.
+      openSessionWindow: (sessionId: string) => Promise<{ ok: boolean; error?: string }>
       getBootProgress: () => Promise<DesktopBootProgress>
       getConnectionConfig: (profile?: null | string) => Promise<DesktopConnectionConfig>
       saveConnectionConfig: (payload: DesktopConnectionConfigInput) => Promise<DesktopConnectionConfig>

apps/desktop/src/i18n/en.ts

@@ -1084,6 +1084,7 @@ export const en: Translations = {
       export: 'Export',
       rename: 'Rename',
       archive: 'Archive',
+      newWindow: 'New window',
       copyIdFailed: 'Could not copy session ID',
       actionsFor: title => `Actions for ${title}`,
       sessionActions: 'Session actions',

apps/desktop/src/i18n/ja.ts

@@ -1218,6 +1218,7 @@ export const ja = defineLocale({
       export: 'エクスポート',
       rename: '名前を変更',
       archive: 'アーカイブ',
+      newWindow: '新しいウィンドウ',
       copyIdFailed: 'セッション ID をコピーできませんでした',
       actionsFor: title => `${title} のアクション`,
       sessionActions: 'セッションアクション',

apps/desktop/src/i18n/types.ts

@@ -832,6 +832,7 @@ export interface Translations {
       export: string
       rename: string
       archive: string
+      newWindow: string
       copyIdFailed: string
       actionsFor: (title: string) => string
       sessionActions: string

apps/desktop/src/i18n/zh-hant.ts

@@ -1184,6 +1184,7 @@ export const zhHant = defineLocale({
       export: '匯出',
       rename: '重新命名',
       archive: '封存',
+      newWindow: '新視窗',
       copyIdFailed: '無法複製工作階段 ID',
       actionsFor: title => `${title} 的動作`,
       sessionActions: '工作階段動作',

apps/desktop/src/i18n/zh.ts

@@ -1271,6 +1271,7 @@ export const zh: Translations = {
       export: '导出',
       rename: '重命名',
       archive: '归档',
+      newWindow: '新窗口',
       copyIdFailed: '无法复制会话 ID',
       actionsFor: title => `${title} 的操作`,
       sessionActions: '会话操作',

apps/desktop/src/store/windows.test.ts

@@ -0,0 +1,93 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+
+import { canOpenSessionWindow, openSessionInNewWindow } from './windows'
+
+const desktopWindow = window as unknown as { hermesDesktop?: Window['hermesDesktop'] }
+const initialHermesDesktop = desktopWindow.hermesDesktop
+
+const notifyError = vi.fn()
+
+vi.mock('./notifications', () => ({
+  notifyError: (...args: unknown[]) => notifyError(...args)
+}))
+
+function installBridge(openSessionWindow?: Window['hermesDesktop']['openSessionWindow']) {
+  desktopWindow.hermesDesktop = {
+    ...(openSessionWindow ? { openSessionWindow } : {})
+  } as unknown as Window['hermesDesktop']
+}
+
+beforeEach(() => {
+  notifyError.mockClear()
+})
+
+afterEach(() => {
+  if (initialHermesDesktop) {
+    desktopWindow.hermesDesktop = initialHermesDesktop
+  } else {
+    delete desktopWindow.hermesDesktop
+  }
+})
+
+describe('canOpenSessionWindow', () => {
+  it('is false when the desktop bridge is absent', () => {
+    delete desktopWindow.hermesDesktop
+    expect(canOpenSessionWindow()).toBe(false)
+  })
+
+  it('is false when the bridge lacks openSessionWindow', () => {
+    installBridge(undefined)
+    expect(canOpenSessionWindow()).toBe(false)
+  })
+
+  it('is true when the bridge exposes openSessionWindow', () => {
+    installBridge(vi.fn().mockResolvedValue({ ok: true }))
+    expect(canOpenSessionWindow()).toBe(true)
+  })
+})
+
+describe('openSessionInNewWindow', () => {
+  it('no-ops without a session id', async () => {
+    const open = vi.fn().mockResolvedValue({ ok: true })
+    installBridge(open)
+
+    await openSessionInNewWindow('')
+
+    expect(open).not.toHaveBeenCalled()
+    expect(notifyError).not.toHaveBeenCalled()
+  })
+
+  it('no-ops gracefully when the bridge is absent (web fallback)', async () => {
+    delete desktopWindow.hermesDesktop
+
+    await openSessionInNewWindow('s1')
+
+    expect(notifyError).not.toHaveBeenCalled()
+  })
+
+  it('invokes the bridge with the session id', async () => {
+    const open = vi.fn().mockResolvedValue({ ok: true })
+    installBridge(open)
+
+    await openSessionInNewWindow('s1')
+
+    expect(open).toHaveBeenCalledWith('s1')
+    expect(notifyError).not.toHaveBeenCalled()
+  })
+
+  it('notifies on an ok:false result', async () => {
+    installBridge(vi.fn().mockResolvedValue({ ok: false, error: 'invalid-session-id' }))
+
+    await openSessionInNewWindow('s1')
+
+    expect(notifyError).toHaveBeenCalledTimes(1)
+  })
+
+  it('notifies when the bridge throws', async () => {
+    installBridge(vi.fn().mockRejectedValue(new Error('boom')))
+
+    await openSessionInNewWindow('s1')
+
+    expect(notifyError).toHaveBeenCalledTimes(1)
+  })
+})

apps/desktop/src/store/windows.ts

@@ -0,0 +1,52 @@
+import { notifyError } from './notifications'
+
+// Window flag set by the Electron main process when it opens a standalone
+// session window (see electron/main.cjs buildSessionWindowUrl). It rides in the
+// query string BEFORE the HashRouter '#', so we read it from location.search,
+// never from the router. A "secondary" window renders a single chat without the
+// global session sidebar or the install / onboarding overlays.
+const SECONDARY_WINDOW_FLAG = 'secondary'
+
+let secondaryWindowCache: boolean | null = null
+
+export function isSecondaryWindow(): boolean {
+  if (secondaryWindowCache !== null) {
+    return secondaryWindowCache
+  }
+
+  let result = false
+
+  try {
+    result = new URLSearchParams(window.location.search).get('win') === SECONDARY_WINDOW_FLAG
+  } catch {
+    result = false
+  }
+
+  secondaryWindowCache = result
+
+  return result
+}
+
+// True when running inside the Electron desktop shell (the preload bridge is
+// present). The "open in new window" affordance is desktop-only.
+export function canOpenSessionWindow(): boolean {
+  return typeof window !== 'undefined' && typeof window.hermesDesktop?.openSessionWindow === 'function'
+}
+
+// Open (or focus) a standalone OS window for a single chat session. No-ops
+// gracefully outside Electron so callers can wire it unconditionally.
+export async function openSessionInNewWindow(sessionId: string): Promise<void> {
+  if (!sessionId || !canOpenSessionWindow()) {
+    return
+  }
+
+  try {
+    const result = await window.hermesDesktop.openSessionWindow(sessionId)
+
+    if (!result?.ok) {
+      notifyError(new Error(result?.error || 'unknown error'), 'Could not open chat in a new window')
+    }
+  } catch (err) {
+    notifyError(err, 'Could not open chat in a new window')
+  }
+}