feat(desktop): shell integration for PowerShell and Git Bash on Windows

The agent terminal was refused with NO_SHELL_INTEGRATION on Windows
because prompt hooks existed only for zsh and bash. PowerShell now gets
the same OSC 633 markers: `prompt` reports the directory, previous exit
code and prompt start, and `PSConsoleHostReadLine` reports each command
line and its start, as Windows Terminal and VS Code do. The hooks travel
as -EncodedCommand because dot-sourcing a file is blocked by the default
execution policy on Windows clients, and ReadLine is called with two
arguments only: PSReadLine 2.0's third parameter is a CancellationToken,
and a bool coerces to a cancelled one, which made the prompt loop.

Git for Windows' bash is offered through a Windows-only Terminal Shell
submenu when Git is installed; the existing bash hooks work there, with
cygpath translating the reported directory to a Windows path. The choice
persists as `terminalShell` in settings.

Also: the marker parser unescapes `\\` so Windows paths survive the
hooks' escaping, tab titles split on either separator, tmux probing is
skipped on Windows, and detectShell recognises `.exe` names on any host.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

Author: Thewookie-Eng

apps/desktop/README.md

@@ -111,7 +111,9 @@ Build on a Windows host (electron-builder cross-compiles NSIS from macOS/Linux o
 - Signing: set `CSC_LINK`/`CSC_KEY_PASSWORD` to an Authenticode `.pfx`; unsigned builds trigger SmartScreen on first launch.
 - Bun does not run electron's `postinstall` on Windows; if `node_modules/electron/dist/electron.exe` is missing after `bun install`, run `node node_modules/electron/install.js` once.
 
-Windows parity gaps (deliberate, see "Known caveats"): no auto-update (the updater is a no-op off macOS — the installer must be re-downloaded), no Help-menu docs search, no Chrome cookie/password import, no Terminal.app/iTerm2 theme import, and the agent terminal launches PowerShell uninstrumented (shell integration is zsh/bash only), so the agent is refused with `NO_SHELL_INTEGRATION` while the user's terminal still works.
+The agent terminal launches PowerShell (`pwsh`, else Windows PowerShell 5.1) with full shell integration: the hooks are passed as `-EncodedCommand` (a dot-sourced file would be blocked by the default execution policy), `prompt` is wrapped to report the directory, exit code and prompt start, and `PSConsoleHostReadLine` is wrapped to report each command line and its start — the arrangement Windows Terminal and VS Code use. Git for Windows' bash is offered under the app menu's **Terminal Shell** submenu when Git is installed; it uses the existing bash hooks, with `cygpath -w` translating the reported directory to a Windows path. The choice persists as `terminalShell` in `settings.json`. tmux integration is skipped on Windows.
+
+Windows parity gaps (deliberate, see "Known caveats"): no auto-update (the updater is a no-op off macOS — the installer must be re-downloaded), no Help-menu docs search, no Chrome cookie/password import, and no Terminal.app/iTerm2 theme import.
 
 Local unsigned pre-release share: `SIM_DESKTOP_DEFAULT_ORIGIN=https://www.dev.sim.ai bun run package:share` builds a DMG whose fresh installs default to that origin (baked at build time; official builds leave it unset → prod) and skips per-file signature timestamps. Recipients must clear quarantine once: `xattr -cr /Applications/Sim.app`.
 

apps/desktop/src/main/config.ts

@@ -3,6 +3,7 @@ import type { DesktopZoomPercent, TerminalAppearanceTheme } from '@sim/desktop-b
 import { createLogger } from '@sim/logger'
 import { isLoopbackHostname } from '@sim/security/ssrf'
 import { writeJsonFileAtomicallySync } from '@/main/atomic-json-file'
+import type { WindowsTerminalShell } from '@/main/terminal/default-shell'
 
 /** settings.json is meant to be readable when a user opens it. */
 const SETTINGS_INDENT = 2
@@ -114,6 +115,8 @@ export interface DesktopSettings {
   terminalTheme?: TerminalAppearanceTheme
   /** Device-wide default zoom for built-in terminal canvases. */
   terminalDefaultZoom?: DesktopZoomPercent
+  /** Windows only: which installed shell new terminals launch. */
+  terminalShell?: WindowsTerminalShell
   /**
    * Top-level sites visited in the dedicated agent-browser profile. This is
    * local inference metadata only; no cookies, credentials, or account data

apps/desktop/src/main/index.ts

@@ -80,6 +80,12 @@ import {
 } from '@/main/session-lifecycle'
 import { setShellTheme } from '@/main/shell-theme'
 import { attachTelemetryPolicy } from '@/main/telemetry-policy'
+import {
+  findGitBash,
+  getPreferredWindowsShell,
+  isWindowsTerminalShell,
+  setPreferredWindowsShell,
+} from '@/main/terminal/default-shell'
 import { TerminalRegistry } from '@/main/terminal/registry'
 import { installTray, type TrayHandle } from '@/main/tray'
 import { checkForUpdatesInteractive, initUpdater, type UpdaterHandle } from '@/main/updater'
@@ -147,6 +153,10 @@ function main(): void {
     ),
   })
   const scopeEvents = new ScopedEventRouter()
+  if (process.platform === 'win32') {
+    const storedShell = config.get('terminalShell')
+    if (isWindowsTerminalShell(storedShell)) setPreferredWindowsShell(storedShell)
+  }
   const terminal = new TerminalRegistry({
     load: (scopeId) => desktopChatSessions.getTerminal(processOrigin, scopeId) ?? undefined,
     save: (scopeId, snapshot) => desktopChatSessions.setTerminal(processOrigin, scopeId, snapshot),
@@ -844,25 +854,39 @@ function main(): void {
       },
     })
     await ensureMainWindow()
-    installApplicationMenu({
-      config,
-      getMainWindow,
-      isMainWindow: (win) => windows.has(win) && !win.isDestroyed(),
-      allowHttpLocalhost,
-      openSettings,
-      openServerSettings: () => serverWindow.open(),
-      newWindow: () => void createAndLoadAppWindow(),
-      newChat: () => void openMainWindowAt(newChatRoute(config.get('lastRoute'))),
-      handleFocusedResourceShortcut: (win, shortcut) =>
-        handleFocusedBrowserShortcut(shortcut, win) ||
-        terminal.handleFocusedShortcut(win, shortcut),
-      toggleSidebar: () => getMainWindow()?.webContents.send('desktop:command', 'toggle-sidebar'),
-      openSearch: () => getMainWindow()?.webContents.send('desktop:command', 'open-search'),
-      signOut: signOutFromMenu,
-      checkForUpdates: () =>
-        checkForUpdatesInteractive({ getWindow: getMainWindow, events, handle: updater }),
-      openDiagnostics: () => shell.showItemInFolder(events.filePath),
-    })
+    // Rebuilt after a shell choice so the radio reflects it; Electron menus
+    // are immutable once built.
+    const installMenu = () =>
+      installApplicationMenu({
+        config,
+        getMainWindow,
+        isMainWindow: (win) => windows.has(win) && !win.isDestroyed(),
+        allowHttpLocalhost,
+        openSettings,
+        openServerSettings: () => serverWindow.open(),
+        newWindow: () => void createAndLoadAppWindow(),
+        newChat: () => void openMainWindowAt(newChatRoute(config.get('lastRoute'))),
+        handleFocusedResourceShortcut: (win, shortcut) =>
+          handleFocusedBrowserShortcut(shortcut, win) ||
+          terminal.handleFocusedShortcut(win, shortcut),
+        toggleSidebar: () => getMainWindow()?.webContents.send('desktop:command', 'toggle-sidebar'),
+        openSearch: () => getMainWindow()?.webContents.send('desktop:command', 'open-search'),
+        signOut: signOutFromMenu,
+        checkForUpdates: () =>
+          checkForUpdatesInteractive({ getWindow: getMainWindow, events, handle: updater }),
+        openDiagnostics: () => shell.showItemInFolder(events.filePath),
+        terminalShell: {
+          current: getPreferredWindowsShell,
+          gitBashAvailable: () => findGitBash() !== null,
+          select: (choice) => {
+            setPreferredWindowsShell(choice)
+            config.set('terminalShell', choice)
+            config.flush()
+            installMenu()
+          },
+        },
+      })
+    installMenu()
     installDocumentationHelpSearch()
     setTrayEnabled(config.get('trayEnabled') ?? true)
     updater = initUpdater({

apps/desktop/src/main/menu.ts

@@ -8,6 +8,7 @@ import type {
   FocusedResourceShortcut,
   ResourceTabSelectionShortcut,
 } from '@/main/resource-shortcuts'
+import { WINDOWS_TERMINAL_SHELLS, type WindowsTerminalShell } from '@/main/terminal/default-shell'
 
 const ZOOM_STEP = 0.5
 
@@ -35,6 +36,38 @@ export interface MenuDeps {
   signOut: () => void
   checkForUpdates: () => void
   openDiagnostics: () => void
+  /**
+   * Windows only: the shell new terminals launch. macOS has one answer
+   * (`$SHELL`), so the submenu exists only where there is a choice to make.
+   */
+  terminalShell?: {
+    current: () => WindowsTerminalShell
+    gitBashAvailable: () => boolean
+    select: (shell: WindowsTerminalShell) => void
+  }
+}
+
+const TERMINAL_SHELL_LABELS: Record<WindowsTerminalShell, string> = {
+  powershell: 'PowerShell',
+  'git-bash': 'Git Bash',
+}
+
+function terminalShellSubmenu(deps: MenuDeps): MenuItemConstructorOptions[] {
+  const choice = deps.terminalShell
+  if (!choice || process.platform !== 'win32') return []
+  const current = choice.current()
+  return [
+    {
+      label: 'Terminal Shell',
+      submenu: WINDOWS_TERMINAL_SHELLS.map((shell) => ({
+        label: TERMINAL_SHELL_LABELS[shell],
+        type: 'radio' as const,
+        checked: shell === current,
+        enabled: shell !== 'git-bash' || choice.gitBashAvailable(),
+        click: () => choice.select(shell),
+      })),
+    },
+  ]
 }
 
 /**
@@ -199,6 +232,7 @@ export function buildMenuTemplate(deps: MenuDeps): MenuItemConstructorOptions[]
         },
         { label: 'Settings…', accelerator: 'CmdOrCtrl+,', click: deps.openSettings },
         { label: 'Server…', click: deps.openServerSettings },
+        ...terminalShellSubmenu(deps),
         { label: 'Check for Updates…', click: deps.checkForUpdates },
         { label: 'Sign Out', click: deps.signOut },
         { type: 'separator' },

apps/desktop/src/main/terminal/default-shell.ts

@@ -5,11 +5,36 @@
  * convention: `COMSPEC` names cmd.exe, which is the shell of last resort, so
  * PowerShell is preferred when it is installed — pwsh (PowerShell 7) first,
  * then the Windows PowerShell 5.1 that ships with every supported Windows.
+ * Git for Windows' bash is offered as an alternative when it is installed,
+ * because the bash shell-integration hooks work in it unchanged.
  */
 import { existsSync } from 'node:fs'
-import { delimiter, join } from 'node:path'
+import { delimiter, dirname, join } from 'node:path'
 
-const WINDOWS_SHELL_CANDIDATES = ['pwsh.exe', 'powershell.exe'] as const
+export type WindowsTerminalShell = 'powershell' | 'git-bash'
+
+export const WINDOWS_TERMINAL_SHELLS: readonly WindowsTerminalShell[] = ['powershell', 'git-bash']
+
+export function isWindowsTerminalShell(value: unknown): value is WindowsTerminalShell {
+  return value === 'powershell' || value === 'git-bash'
+}
+
+const WINDOWS_POWERSHELL_CANDIDATES = ['pwsh.exe', 'powershell.exe'] as const
+
+/**
+ * The shell the next Windows terminal launches. Process-wide rather than
+ * threaded through every service because the choice is a device preference,
+ * like the terminal theme, and every chat scope's shells share it.
+ */
+let preferredWindowsShell: WindowsTerminalShell = 'powershell'
+
+export function setPreferredWindowsShell(shell: WindowsTerminalShell): void {
+  preferredWindowsShell = shell
+}
+
+export function getPreferredWindowsShell(): WindowsTerminalShell {
+  return preferredWindowsShell
+}
 
 function findOnPath(executable: string, env: NodeJS.ProcessEnv): string | null {
   for (const directory of (env.PATH ?? env.Path ?? '').split(delimiter)) {
@@ -20,16 +45,54 @@ function findOnPath(executable: string, env: NodeJS.ProcessEnv): string | null {
   return null
 }
 
+/**
+ * Git for Windows' bash, or null when Git is not installed.
+ *
+ * Only Git's own install locations are checked. A bare `bash.exe` on PATH is
+ * not trusted: `C:\Windows\System32\bash.exe` is the WSL launcher, which runs
+ * a Linux VM rather than a shell on this machine.
+ */
+export function findGitBash(env: NodeJS.ProcessEnv = process.env): string | null {
+  const roots = [
+    env.ProgramFiles,
+    env['ProgramFiles(x86)'],
+    env.ProgramW6432,
+    env.LOCALAPPDATA ? join(env.LOCALAPPDATA, 'Programs') : undefined,
+  ]
+  for (const root of roots) {
+    if (!root) continue
+    const candidate = join(root, 'Git', 'bin', 'bash.exe')
+    if (existsSync(candidate)) return candidate
+  }
+  // A Git installed elsewhere still puts `cmd\git.exe` on PATH; bash sits
+  // beside it in the install's `bin`.
+  const git = findOnPath('git.exe', env)
+  if (git) {
+    const candidate = join(dirname(dirname(git)), 'bin', 'bash.exe')
+    if (existsSync(candidate)) return candidate
+  }
+  return null
+}
+
+function findPowerShell(env: NodeJS.ProcessEnv): string | null {
+  for (const executable of WINDOWS_POWERSHELL_CANDIDATES) {
+    const found = findOnPath(executable, env)
+    if (found) return found
+  }
+  return null
+}
+
 export function defaultShellPath(
   env: NodeJS.ProcessEnv = process.env,
-  platform: NodeJS.Platform = process.platform
+  platform: NodeJS.Platform = process.platform,
+  preference: WindowsTerminalShell = preferredWindowsShell
 ): string {
   if (platform !== 'win32') {
     return env.SHELL || '/bin/zsh'
   }
-  for (const executable of WINDOWS_SHELL_CANDIDATES) {
-    const found = findOnPath(executable, env)
-    if (found) return found
+  if (preference === 'git-bash') {
+    const gitBash = findGitBash(env)
+    if (gitBash) return gitBash
   }
-  return env.COMSPEC || 'cmd.exe'
+  return findPowerShell(env) ?? env.COMSPEC ?? 'cmd.exe'
 }

apps/desktop/src/main/terminal/session.ts

@@ -443,7 +443,7 @@ export class TerminalSession {
    * at a glance.
    */
   tabState(active: boolean): TerminalTabState {
-    const directory = this.cwd ? (this.cwd.split('/').filter(Boolean).pop() ?? '/') : null
+    const directory = this.cwd ? (this.cwd.split(/[\\/]/).filter(Boolean).pop() ?? '/') : null
     return {
       terminalId: this.terminalId,
       // The directory, always: whether to show the running command instead is

apps/desktop/src/main/terminal/shell-integration.test.ts

@@ -86,6 +86,11 @@ describe('detectShell', () => {
   it('recognises the shells we can instrument', () => {
     expect(detectShell('/bin/zsh')).toBe('zsh')
     expect(detectShell('/usr/local/bin/bash')).toBe('bash')
+    expect(detectShell('C:\\Program Files\\Git\\bin\\bash.exe')).toBe('bash')
+    expect(detectShell('C:\\WINDOWS\\System32\\WindowsPowerShell\\v1.0\\powershell.exe')).toBe(
+      'powershell'
+    )
+    expect(detectShell('C:\\Program Files\\PowerShell\\7\\pwsh.exe')).toBe('powershell')
   })
 
   it('returns null for shells without hooks, leaving the terminal uninstrumented', () => {