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