fix(launch-prompt): plan a WSL pane for its own shell; refuse a launch that cannot be staged

Stack QA on 193eeaddff:
- A WSL workspace added by its \\wsl.localhost path was planned as a Windows
  launch, so the Windows shell setting decided its line: under cmd, Claude's
  pointer was cmd-quoted and bash ran the backticked path, losing the prompt;
  the carry also changed with the setting. A WSL path now plans as the distro
  (POSIX quoting, WSL staging up to 100,000 bytes), and a pane whose Windows
  shell is wsl.exe is a host fact (windowsPaneShell) the rule reads.
- A Tab or bare carriage return was measured exact on both PowerShells and is
  no longer counted as damage there; cmd and Git Bash still damage it, and an
  unmeasured control byte does what main does on that path.
- The WSL folder probe kept a success forever. A refused spawn now forgets it,
  and the daemon refuses an agent launch whose line it could not stage
  (launch_file_unavailable) instead of typing it in full.

src/main/daemon/daemon-pty-session-spawn.ts

@@ -18,7 +18,10 @@ import { getRecoveredHistorySeedSegments } from './terminal-history-seed-segment
 import { AGENT_SESSION_CLAIM_DAEMON_PROTOCOL_VERSION, type CreateOrAttachResult } from './types'
 import { normalizeWslColdRestoreCwd } from './wsl-cold-restore-cwd'
 import { resolveWslSessionContext } from './wsl-session-context'
-import { resolveSpawnWslLaunchDirectory } from '../providers/wsl-launch-directory-resolution'
+import {
+  forgetWslLaunchDirectoryAfterRefusal,
+  resolveSpawnWslLaunchDirectory
+} from '../providers/wsl-launch-directory-resolution'
 import { resolveSafePtyDefaultCwd } from '../providers/pty-default-cwd'
 import { resolveUnixShellPath } from '../providers/local-pty-utils'
 import type { PtySpawnOptions, PtySpawnResult } from '../providers/types'
@@ -258,7 +261,13 @@ export abstract class DaemonPtySessionSpawn extends DaemonPtySpawnResult {
       detectColdRestore
     }
     activeSpawnContext = context
-    const result = await this.createOrAttachSpawn(context, context.historySeedSegments)
+    let result
+    try {
+      result = await this.createOrAttachSpawn(context, context.historySeedSegments)
+    } catch (error) {
+      forgetWslLaunchDirectoryAfterRefusal(wslLaunchDirectory, error)
+      throw error
+    }
     if (result.isNew && !attachOnly) {
       // Not awaited: the app-side read behind it can sit on an unanswered macOS folder prompt.
       void reportDaemonPtyCwdVerdict({

src/main/daemon/terminal-host-session-create.ts

@@ -6,7 +6,11 @@ import {
   type StartupCommandStaging
 } from '../../shared/startup-command-staging'
 import { resolvePtyOwnerBackend } from '../../shared/pty-owner-backend'
-import { removeLaunchFile, writeSpawnLaunchFile } from '../../shared/launch-file-writing'
+import {
+  LaunchFileUnavailableError,
+  removeLaunchFile,
+  writeSpawnLaunchFile
+} from '../../shared/launch-file-writing'
 import { getDaemonSessionResultMetadata } from './daemon-create-or-attach-result'
 import { enumerateDirectoryOnce } from './directory-enumeration-probe'
 import { normalizePtySize } from './daemon-pty-size'
@@ -206,11 +210,33 @@ async function spawnAndPublishSession(
     throw new TerminalAttachCanceledError(opts.sessionId)
   }
 
+  const startupCommandWritten = Boolean(command) && !subprocess.startupCommandDeliveredInShellArgs
+  if (startupCommandWritten && command) {
+    staging = stageStartupCommand({
+      command,
+      shellPath: subprocess.shellPath,
+      orcaBuiltLine: opts.launchAgent !== undefined,
+      wslDirectory
+    })
+    // Why refuse: typed in full, a long agent line can leave the shell at a quote prompt with the
+    // prompt lost while the launch reports success; the refusal hands the user the prompt instead.
+    if (staging.failure !== undefined && opts.launchAgent !== undefined) {
+      deps.sessions.set(opts.sessionId, session)
+      await session.forceKillAndDisposeSubprocess()
+      removeLaunchFile(launchFile)
+      if (deps.sessions.get(opts.sessionId) === session) {
+        session.dispose()
+        deps.sessions.delete(opts.sessionId)
+        deps.onDeadSessionRemoved(opts.sessionId)
+      }
+      throw new LaunchFileUnavailableError(staging.failure, 'staged-line')
+    }
+  }
+
   deps.sessions.set(opts.sessionId, session)
   deps.onSessionCreated(opts.sessionId, opts.agentSessionGeneration, session.isAlive)
   const token = session.attachClient(opts.streamClient)
 
-  const startupCommandWritten = Boolean(command) && !subprocess.startupCommandDeliveredInShellArgs
   // Why: without this, a missing command and a lost one log identically.
   // Length, never the text -- launches can carry credentials.
   try {
@@ -225,13 +251,7 @@ async function spawnAndPublishSession(
   } catch {
     // Diagnostics must never turn a live PTY into a failed create.
   }
-  if (startupCommandWritten && command) {
-    staging = stageStartupCommand({
-      command,
-      shellPath: subprocess.shellPath,
-      orcaBuiltLine: opts.launchAgent !== undefined,
-      wslDirectory
-    })
+  if (staging) {
     const notice = startupStagingFailureNotice(staging)
     if (notice) {
       session.startupIngress.accept(notice)

src/main/daemon/terminal-host-startup-staging.test.ts

@@ -99,6 +99,31 @@ describePosix('daemon startup command staging', () => {
     expect(sub.write).not.toHaveBeenCalled()
   })
 
+  // Why (stack QA P8-2): typed in full, a long agent line left the shell at a quote prompt, the
+  // prompt lost while agent.launch reported success; refusing hands the user the prompt instead.
+  it('refuses an agent launch it could not stage, typing nothing and keeping no session', async () => {
+    vi.stubEnv('TMPDIR', join(tempDir, 'missing'))
+    const sub = mockSubprocess('/bin/zsh')
+    vi.mocked(sub.forceKill).mockImplementation(() => exitSubprocess?.(1))
+    vi.mocked(sub.kill).mockImplementation(() => exitSubprocess?.(1))
+    const host = new TerminalHost({ spawnSubprocess: () => sub })
+    await expect(
+      host.createOrAttach({
+        sessionId: 's-agent-stage-failed',
+        cols: 80,
+        rows: 24,
+        command: `claude '${'x'.repeat(600)}'`,
+        launchAgent: 'claude',
+        shellReadySupported: false,
+        streamClient: { onData: vi.fn(), onExit: vi.fn() }
+      })
+    ).rejects.toThrow(/launch_file_unavailable/)
+    expect(sub.write).not.toHaveBeenCalled()
+    expect(host.listSessions().map((session) => session.sessionId)).not.toContain(
+      's-agent-stage-failed'
+    )
+  })
+
   it('prints a notice in the terminal when it types a line it could not stage', async () => {
     vi.stubEnv('TMPDIR', join(tempDir, 'missing'))
     const command = `claude '${'x'.repeat(600)}'`

src/main/providers/local-pty-spawn.ts

@@ -30,7 +30,10 @@ import {
   writeSpawnLaunchFile,
   type WrittenLaunchFile
 } from '../../shared/launch-file-writing'
-import { resolveSpawnWslLaunchDirectory } from './wsl-launch-directory-resolution'
+import {
+  forgetWslLaunchDirectoryAfterRefusal,
+  resolveSpawnWslLaunchDirectory
+} from './wsl-launch-directory-resolution'
 
 export async function spawnLocalPty(
   args: PtySpawnOptions,
@@ -55,14 +58,20 @@ export async function spawnLocalPty(
   if (args.attachOnly) {
     throw new SessionNotFoundError(args.sessionId ?? '')
   }
-  const launchFile = writeSpawnLaunchFile({
-    launchFile: args.launchFile,
-    command: args.command,
-    env: args.env,
-    orcaBuiltLine: args.launchAgent !== undefined,
-    wslDistro,
-    wslDirectory: wslLaunchDirectory
-  })
+  let launchFile: WrittenLaunchFile | undefined
+  try {
+    launchFile = writeSpawnLaunchFile({
+      launchFile: args.launchFile,
+      command: args.command,
+      env: args.env,
+      orcaBuiltLine: args.launchAgent !== undefined,
+      wslDistro,
+      wslDirectory: wslLaunchDirectory
+    })
+  } catch (error) {
+    forgetWslLaunchDirectoryAfterRefusal(wslLaunchDirectory, error)
+    throw error
+  }
   args = {
     ...args,
     ...(launchFile ? { command: launchFile.command, env: launchFile.env } : {}),
@@ -75,6 +84,7 @@ export async function spawnLocalPty(
     return await spawnFreshLocalPty(args, getOptions, reattachId, launchFile)
   } catch (error) {
     removeLaunchFile(launchFile)
+    forgetWslLaunchDirectoryAfterRefusal(wslLaunchDirectory, error)
     throw error
   }
 }

src/main/providers/wsl-launch-directory-resolution.test.ts

@@ -3,6 +3,7 @@ import { createLocalPtyLaunchPlan, resolveLocalPtyWslDistro } from './local-pty-
 import type { LocalPtyProviderOptions } from './local-pty-provider-types'
 import type { PtySpawnOptions } from './types'
 import {
+  forgetWslLaunchDirectoryAfterRefusal,
   resolveSpawnWslLaunchDirectory,
   resolveWslLaunchDirectory,
   WSL_LAUNCH_DIRECTORY_FAILURE_TTL_MS
@@ -81,6 +82,23 @@ describe('resolveWslLaunchDirectory', () => {
     }
   })
 
+  // Why (stack QA P8-2): a folder found once and broken later must not be written into forever.
+  it('asks the distro again after a write into the found folder was refused', async () => {
+    runWslProcess.mockResolvedValue(answers('/home/ada\n/bin/bash\n'))
+    const found = await resolveWslLaunchDirectory('Void')
+    forgetWslLaunchDirectoryAfterRefusal(found, new Error('EACCES'))
+    await resolveWslLaunchDirectory('Void')
+    expect(runWslProcess).toHaveBeenCalledTimes(1)
+    forgetWslLaunchDirectoryAfterRefusal(
+      found,
+      new Error(
+        'Orca could not write it (EEXIST), so the agent was not started. [launch_file_unavailable]'
+      )
+    )
+    await resolveWslLaunchDirectory('Void')
+    expect(runWslProcess).toHaveBeenCalledTimes(2)
+  })
+
   it('probes only for a spawn that needs the directory', async () => {
     runWslProcess.mockResolvedValue(answers('/home/ada\n/bin/bash\n'))
     expect(

src/main/providers/wsl-launch-directory-resolution.ts

@@ -3,6 +3,7 @@ import { quotePosixShell, RESOLVE_WSL_LOGIN_SHELL } from '../../shared/wsl-login
 import type { WslLaunchDirectory } from '../../shared/wsl-launch-directory'
 import type { LaunchFile } from '../../shared/launch-prompt-file'
 import { spawnNeedsWslLaunchDirectory } from '../../shared/launch-file-writing'
+import { isLaunchFileRefusal } from '../../shared/launch-prompt-file'
 import type { TuiAgent } from '../../shared/tui-agent'
 import { toWindowsWslUncPath } from '../../shared/wsl-paths'
 import { runWslProcess } from '../wsl/wsl-runner'
@@ -40,7 +41,8 @@ export function resolveSpawnWslLaunchDirectory(
  * The distro directory a WSL spawn's staged line and launch file are written to, and the login
  * shell the pane runs, which decides how a staged line is sourced; undefined when the distro cannot
  * be asked, and the write site then refuses a launch that needs one. Probed once per distro; a
- * success is kept, a failure for `WSL_LAUNCH_DIRECTORY_FAILURE_TTL_MS`.
+ * success is kept until a write into it fails (`forgetWslLaunchDirectoryAfterRefusal`), a failure
+ * for `WSL_LAUNCH_DIRECTORY_FAILURE_TTL_MS`.
  */
 export async function resolveWslLaunchDirectory(
   distro: string | null | undefined
@@ -66,6 +68,17 @@ export async function resolveWslLaunchDirectory(
   return await probe
 }
 
+/** A spawn into this directory was refused: forget it, so the next launch asks the distro again
+ *  rather than writing into a folder that stopped working. */
+export function forgetWslLaunchDirectoryAfterRefusal(
+  directory: WslLaunchDirectory | undefined,
+  error: unknown
+): void {
+  if (directory && isLaunchFileRefusal(error)) {
+    probes.delete(directory.distro)
+  }
+}
+
 async function probeWslLaunchDirectory(distro: string): Promise<WslLaunchDirectory | undefined> {
   const script = [
     ...RESOLVE_WSL_LOGIN_SHELL,

src/main/runtime/runtime-agent-launch-resolution.ts

@@ -5,6 +5,7 @@ import type { SleepingAgentLaunchConfig } from '../../shared/agent-session-resum
 import type { ClaudeAgentTeamsMode } from '../../shared/claude-agent-teams-tmux-compat'
 import type { ProjectExecutionRuntimeResolution } from '../../shared/project-execution-runtime'
 import { isWindowsAbsolutePathLike } from '../../shared/cross-platform-path'
+import { isWslUncPath } from '../../shared/wsl-paths'
 import { getTuiAgentLaunchCommand, TUI_AGENT_CONFIG } from '../../shared/tui-agent-config'
 import { isTuiAgentEnabled } from '../../shared/tui-agent-selection'
 
@@ -110,7 +111,12 @@ export function getAgentLaunchPlatformForRepo(
     if (projectRuntime?.status === 'repair-required') {
       return projectRuntime.repair.preferredRuntime.kind === 'wsl' ? 'linux' : process.platform
     }
-    if (projectRuntime?.status === 'resolved' && projectRuntime.runtime.kind === 'wsl') {
+    // Why a WSL path: the pane spawns in the distro's POSIX shell, whatever the Windows shell
+    // setting, so its line is judged and quoted for that shell.
+    if (
+      (projectRuntime?.status === 'resolved' && projectRuntime.runtime.kind === 'wsl') ||
+      isWslUncPath(repo.path)
+    ) {
       return 'linux'
     }
     return process.platform

src/main/runtime/this-orca-launch-host.test.ts

@@ -30,12 +30,12 @@ describe('the PowerShell a launch this Orca runs lands in', () => {
         settings,
         windowsShellOverride
       })
-    expect(host().windowsPowerShell).toBeNull()
+    expect(host().windowsPaneShell).toBeNull()
     vi.mocked(cachedPwshAvailability).mockReturnValue(false)
-    expect(host().windowsPowerShell).toBe('powershell.exe')
-    expect(host('pwsh.exe').windowsPowerShell).toBe('pwsh.exe')
+    expect(host().windowsPaneShell).toBe('powershell.exe')
+    expect(host('pwsh.exe').windowsPaneShell).toBe('pwsh.exe')
     expect(
-      thisOrcaLaunchHost({ launchPlatform: 'win32', isRemote: true, settings }).windowsPowerShell
+      thisOrcaLaunchHost({ launchPlatform: 'win32', isRemote: true, settings }).windowsPaneShell
     ).toBeNull()
   })
 
@@ -47,7 +47,7 @@ describe('the PowerShell a launch this Orca runs lands in', () => {
         launchPlatform: 'win32',
         isRemote: false,
         settings: { terminalWindowsShell: 'pwsh.exe' }
-      }).windowsPowerShell
+      }).windowsPaneShell
     ).toBeNull()
   })
 })

src/main/runtime/this-orca-launch-host.ts

@@ -1,7 +1,7 @@
 import { cachedPwshAvailability } from '../pwsh'
 import {
   describeLaunchHost,
-  spawnedWindowsPowerShell,
+  spawnedWindowsShell,
   type LaunchHost,
   type WindowsShellSettings
 } from '../../shared/launch-host'
@@ -20,8 +20,8 @@ export function thisOrcaLaunchHost(args: {
     isRemote: args.isRemote,
     hostPlatform: process.platform,
     paired: false,
-    windowsPowerShell: local
-      ? spawnedWindowsPowerShell({
+    windowsPaneShell: local
+      ? spawnedWindowsShell({
           settings: args.settings,
           windowsShellOverride: args.windowsShellOverride,
           pwshAvailable: cachedPwshAvailability()

src/main/runtime/wsl-pane-launch-carry.test.ts

@@ -0,0 +1,84 @@
+import { describe, expect, it } from 'vitest'
+import { resolveAgentStartupPlanInputs } from '../../shared/agent-startup-plan-inputs'
+import { describeLaunchHost } from '../../shared/launch-host'
+import { planLaunchPrompt } from '../../shared/tui-agent-startup'
+import { getAgentLaunchPlatformForRepo } from './runtime-agent-launch-resolution'
+
+// The stack QA's WSL workspace: a folder repo added by its distro path (P8-6).
+const WSL_REPO = { connectionId: null, path: '\\\\wsl.localhost\\qasfwin\\root\\fixture' }
+const P25K = 'QA-STACK P25K one line, inert. '.padEnd(25_600, 'x')
+
+function plan(prompt: string, terminalWindowsShell: string) {
+  const platform = getAgentLaunchPlatformForRepo(WSL_REPO)
+  return planLaunchPrompt({
+    ...resolveAgentStartupPlanInputs({
+      agent: 'claude',
+      settings: { terminalWindowsShell },
+      platform,
+      isRemote: false
+    }),
+    prompt,
+    host: describeLaunchHost({
+      launchPlatform: platform,
+      isRemote: false,
+      hostPlatform: 'win32',
+      paired: false
+    }),
+    paste: 'when-host-proves-agent'
+  })
+}
+
+// Why: the pane runs the distro's POSIX shell, so the Windows shell setting must not decide how the
+// line is judged or quoted; quoted for cmd, bash ran the pointer's backticked path and lost it.
+describe('a launch into a WSL workspace, whatever the Windows shell setting', () => {
+  it('is planned for the distro', () => {
+    expect(getAgentLaunchPlatformForRepo(WSL_REPO)).toBe('linux')
+  })
+
+  it.each(['powershell.exe', 'git-bash', 'cmd.exe'])(
+    'stages a 25 KB prompt on a POSIX line under %s',
+    (terminalWindowsShell) => {
+      const planned = plan(P25K, terminalWindowsShell)
+      expect(planned?.carry).toBe('on-line')
+      expect(planned?.carry === 'on-line' && planned.plan.launchCommand).toMatch(
+        new RegExp(`^claude .* '${P25K}'$`)
+      )
+    }
+  )
+
+  it.each(['powershell.exe', 'cmd.exe'])(
+    'keeps $ and backticks literal on the line under %s',
+    (terminalWindowsShell) => {
+      const prompt = 'print $HOME and `id` as text'
+      const planned = plan(prompt, terminalWindowsShell)
+      // POSIX single quotes: bash expands neither `$HOME` nor the backticks inside them.
+      expect(planned?.carry === 'on-line' && planned.plan.launchCommand).toMatch(
+        /^claude .* 'print \$HOME and `id` as text'$/
+      )
+    }
+  )
+})
+
+// Why: a pane whose Windows shell is WSL runs the same POSIX shell, staged by the host.
+describe('a WSL pane on a Windows workspace', () => {
+  it('judges its line by the distro, not by Git Bash', () => {
+    const planned = planLaunchPrompt({
+      ...resolveAgentStartupPlanInputs({
+        agent: 'claude',
+        settings: { terminalWindowsShell: 'wsl.exe' },
+        platform: 'win32',
+        isRemote: false
+      }),
+      prompt: P25K,
+      host: describeLaunchHost({
+        launchPlatform: 'win32',
+        isRemote: false,
+        hostPlatform: 'win32',
+        paired: false,
+        windowsPaneShell: 'wsl.exe'
+      }),
+      paste: 'when-host-proves-agent'
+    })
+    expect(planned?.carry).toBe('on-line')
+  })
+})

src/renderer/src/hooks/composer-state/full-creation-startup.test.ts

@@ -20,7 +20,7 @@ describe('the full composer’s renderer-spawned startup', () => {
           paired: false,
           provesAgentInFront: true,
           takesLaunchFile: true,
-          windowsPowerShell: null
+          windowsPaneShell: null
         },
         paste: 'when-host-proves-agent'
       }),

src/renderer/src/lib/agent-launch-platform.test.ts

@@ -0,0 +1,23 @@
+import { describe, expect, it, vi } from 'vitest'
+import { getAgentLaunchPlatformForRepo } from './agent-launch-platform'
+
+vi.mock('@/lib/new-workspace', () => ({ CLIENT_PLATFORM: 'win32' }))
+
+// Why (stack QA P8-6): a pane in a WSL path runs the distro's POSIX shell, so the desktop must plan
+// its line for that shell, not for the Windows shell setting.
+describe('the platform a desktop launch is planned for', () => {
+  it('is the distro for a workspace in a WSL path', () => {
+    expect(
+      getAgentLaunchPlatformForRepo({
+        connectionId: null,
+        path: '\\\\wsl.localhost\\qasfwin\\root\\fixture'
+      })
+    ).toBe('linux')
+  })
+
+  it('stays this machine for a native path', () => {
+    expect(getAgentLaunchPlatformForRepo({ connectionId: null, path: 'C:\\src\\repo' })).toBe(
+      'win32'
+    )
+  })
+})

src/renderer/src/lib/agent-launch-platform.ts

@@ -1,4 +1,5 @@
 import { isWindowsAbsolutePathLike } from '../../../shared/cross-platform-path'
+import { isWslUncPath } from '../../../shared/wsl-paths'
 import { CLIENT_PLATFORM } from '@/lib/new-workspace'
 import type { AppState } from '@/store'
 import type { ProjectExecutionRuntimeResolution } from '../../../shared/project-execution-runtime'
@@ -11,7 +12,12 @@ export function getAgentLaunchPlatformForRepo(
     if (projectRuntime?.status === 'repair-required') {
       return projectRuntime.repair.preferredRuntime.kind === 'wsl' ? 'linux' : CLIENT_PLATFORM
     }
-    if (projectRuntime?.status === 'resolved' && projectRuntime.runtime.kind === 'wsl') {
+    // Why a WSL path: the pane spawns in the distro's POSIX shell, whatever the Windows shell
+    // setting, so its line is judged and quoted for that shell.
+    if (
+      (projectRuntime?.status === 'resolved' && projectRuntime.runtime.kind === 'wsl') ||
+      isWslUncPath(repo.path)
+    ) {
       return 'linux'
     }
     return CLIENT_PLATFORM

src/renderer/src/lib/launch-file-host.test.ts

@@ -34,7 +34,7 @@ describe('the quick composer on a paired host', () => {
         paired: true,
         provesAgentInFront: true,
         takesLaunchFile: false,
-        windowsPowerShell: null
+        windowsPaneShell: null
       },
       telemetrySource: 'sidebar'
     })
@@ -62,12 +62,12 @@ describe('the PowerShell a local Windows launch from this client lands in', () =
         terminalWindowsPowerShellImplementation: 'auto'
       }
     })
-    expect(host().windowsPowerShell).toBeNull()
+    expect(host().windowsPaneShell).toBeNull()
     vi.mocked(localPwshAvailability).mockReturnValue(false)
-    expect(host().windowsPowerShell).toBe('powershell.exe')
+    expect(host().windowsPaneShell).toBe('powershell.exe')
     vi.mocked(localPwshAvailability).mockReturnValue(true)
-    expect(host().windowsPowerShell).toBe('pwsh.exe')
-    expect(host(true).windowsPowerShell).toBeNull()
+    expect(host().windowsPaneShell).toBe('pwsh.exe')
+    expect(host(true).windowsPaneShell).toBeNull()
     useAppStore.setState({ settings })
   })
 })

src/renderer/src/lib/launch-file-host.ts

@@ -3,7 +3,7 @@ import { CLIENT_PLATFORM } from '@/lib/new-workspace'
 import { useAppStore } from '@/store'
 import {
   describeLaunchHost,
-  spawnedWindowsPowerShell,
+  spawnedWindowsShell,
   type LaunchHost
 } from '../../../shared/launch-host'
 import { isWebClientLocation } from './web-client-location'
@@ -32,8 +32,8 @@ export function clientLaunchHost(args: {
     hostPlatform: CLIENT_PLATFORM,
     paired,
     // Why this client's settings: a local pane is spawned from them, as its shell is.
-    windowsPowerShell: local
-      ? spawnedWindowsPowerShell({
+    windowsPaneShell: local
+      ? spawnedWindowsShell({
           settings: useAppStore.getState().settings,
           pwshAvailable: localPwshAvailability()
         })

src/renderer/src/lib/launch-work-item-direct-agent.test.ts

@@ -88,7 +88,7 @@ describe('buildDirectWorkItemAgentStartupPlan', () => {
         paired: false,
         provesAgentInFront: true,
         takesLaunchFile: true,
-        windowsPowerShell: null
+        windowsPaneShell: null
       },
       agent: 'codex',
       draftContent: 'Review issue 42',
@@ -108,7 +108,7 @@ describe('buildDirectWorkItemAgentStartupPlan', () => {
         paired: false,
         provesAgentInFront: true,
         takesLaunchFile: true,
-        windowsPowerShell: null
+        windowsPaneShell: null
       },
       agent: 'codex',
       draftContent: 'Review issue 42',
@@ -162,7 +162,7 @@ describe('buildDirectWorkItemAgentStartupPlan global arguments fallback', () =>
         paired: false,
         provesAgentInFront: true,
         takesLaunchFile: true,
-        windowsPowerShell: null
+        windowsPaneShell: null
       },
       agent: 'codex',
       draftContent: 'Fix the broken checks',
@@ -181,7 +181,7 @@ describe('buildDirectWorkItemAgentStartupPlan global arguments fallback', () =>
         paired: false,
         provesAgentInFront: true,
         takesLaunchFile: true,
-        windowsPowerShell: null
+        windowsPaneShell: null
       },
       agent: 'codex',
       agentArgs: '--model gpt-5',
@@ -200,7 +200,7 @@ describe('buildDirectWorkItemAgentStartupPlan global arguments fallback', () =>
 describe('buildDirectWorkItemAgentStartupPlan submitted prompts', () => {
   const submit = (agent: 'claude' | 'gemini', draftContent: string, paired = false) =>
     buildDirectWorkItemAgentStartupPlan({
-      host: { paired, provesAgentInFront: true, takesLaunchFile: !paired, windowsPowerShell: null },
+      host: { paired, provesAgentInFront: true, takesLaunchFile: !paired, windowsPaneShell: null },
       agent,
       draftContent,
       promptDelivery: 'submit-after-ready',

src/shared/launch-host.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest'
-import { describeLaunchHost, spawnedWindowsPowerShell } from './launch-host'
+import { describeLaunchHost, spawnedWindowsShell } from './launch-host'
 
 describe('what a launch host can do with its prompt', () => {
   it.each([
@@ -20,14 +20,14 @@ describe('what a launch host can do with its prompt', () => {
         paired,
         provesAgentInFront: proves,
         takesLaunchFile,
-        windowsPowerShell: null
+        windowsPaneShell: null
       })
     }
   )
 })
 
 // Why: the PowerShell decides how `"` and a trailing `\` reach the agent, and this Orca picks it.
-describe('the PowerShell a local Windows pane is spawned as', () => {
+describe('the shell a local Windows pane is spawned as', () => {
   it.each([
     ['the pwsh shell', { terminalWindowsShell: 'pwsh.exe' }, undefined, null, 'pwsh.exe'],
     [
@@ -68,12 +68,21 @@ describe('the PowerShell a local Windows pane is spawned as', () => {
       null,
       null
     ],
-    ['cmd', { terminalWindowsShell: 'cmd.exe' }, undefined, true, null],
-    ['Git Bash', { terminalWindowsShell: 'git-bash' }, undefined, true, null]
+    ['cmd', { terminalWindowsShell: 'cmd.exe' }, undefined, true, 'cmd.exe'],
+    ['Git Bash', { terminalWindowsShell: 'git-bash' }, undefined, true, 'git-bash'],
+    // The distro's POSIX shell, whatever PowerShell would have been.
+    ['WSL', { terminalWindowsShell: 'wsl.exe' }, undefined, true, 'wsl.exe'],
+    [
+      'a requested WSL over a cmd setting',
+      { terminalWindowsShell: 'cmd.exe' },
+      'wsl',
+      null,
+      'wsl.exe'
+    ],
+    // Why unknown: System32's bash.exe is WSL, Git's is Git Bash.
+    ['a bare bash.exe', { terminalWindowsShell: 'bash.exe' }, undefined, true, null]
   ] as const)('%s', (_label, settings, windowsShellOverride, pwshAvailable, expected) => {
-    expect(spawnedWindowsPowerShell({ settings, windowsShellOverride, pwshAvailable })).toBe(
-      expected
-    )
+    expect(spawnedWindowsShell({ settings, windowsShellOverride, pwshAvailable })).toBe(expected)
   })
 
   it('is not this machine’s to know for an SSH or paired host', () => {
@@ -86,8 +95,8 @@ describe('the PowerShell a local Windows pane is spawned as', () => {
           ...where,
           launchPlatform: 'win32',
           hostPlatform: 'win32',
-          windowsPowerShell: 'powershell.exe'
-        }).windowsPowerShell
+          windowsPaneShell: 'powershell.exe'
+        }).windowsPaneShell
       ).toBeNull()
     }
   })

src/shared/launch-host.ts

@@ -1,7 +1,11 @@
 import type { GlobalSettings } from './global-settings-types'
+import { WINDOWS_GIT_BASH_SHELL } from './windows-terminal-shell'
 
 export type WindowsPowerShell = 'powershell.exe' | 'pwsh.exe'
 
+/** The shell a local Windows pane runs; `wsl.exe` is the distro's POSIX login shell. */
+export type WindowsPaneShell = WindowsPowerShell | 'cmd.exe' | 'git-bash' | 'wsl.exe'
+
 export type WindowsShellSettings =
   | Partial<
       Pick<GlobalSettings, 'terminalWindowsShell' | 'terminalWindowsPowerShellImplementation'>
@@ -21,29 +25,39 @@ export type LaunchHost = {
    *  SSH Windows host's relay may run its panes in WSL (its OpenSSH default shell, which this client
    *  cannot see), where it writes none. Such a host gets the line or the paste instead. */
   takesLaunchFile: boolean
-  /** The PowerShell a local Windows pane is spawned as, which decides how it hands `"` and a
-   *  trailing `\` to the agent. Null where this Orca does not choose it (an SSH or paired host) or
-   *  has not yet learned whether pwsh is installed. */
-  windowsPowerShell: WindowsPowerShell | null
+  /** The shell a local Windows pane is spawned as, which the line is judged and quoted by: a WSL
+   *  pane runs the distro's POSIX shell whatever the Windows setting, and the PowerShell decides
+   *  how `"` and a trailing `\` reach the agent. Null where this Orca does not choose it (an SSH or
+   *  paired host), or has not yet learned whether pwsh is installed. */
+  windowsPaneShell: WindowsPaneShell | null
 }
 
 /**
- * The PowerShell this host spawns for a pane, resolved as the spawn resolves it: the requested
- * shell, then the implementation setting, then whether pwsh.exe is installed. Null for a shell that
- * is not PowerShell, or when that probe has not answered.
+ * The shell this host spawns for a local Windows pane, resolved as the spawn resolves it: the
+ * requested shell, then the setting; for PowerShell, the implementation setting, then whether
+ * pwsh.exe is installed. Null for a shell it cannot name (a custom path, or `bash.exe`, which may be
+ * Git Bash or WSL), or a PowerShell before that probe answers.
  */
-export function spawnedWindowsPowerShell(args: {
+export function spawnedWindowsShell(args: {
   settings: WindowsShellSettings
   /** The shell this launch asked for, which outranks the setting. */
   windowsShellOverride?: string | null
   pwshAvailable: boolean | null
-}): WindowsPowerShell | null {
+}): WindowsPaneShell | null {
   const shell = (args.windowsShellOverride ?? args.settings?.terminalWindowsShell ?? '').trim()
-  const name = shell.replaceAll('\\', '/').split('/').pop()?.toLowerCase() ?? ''
-  if (name === 'pwsh.exe' || name === 'pwsh') {
-    return 'pwsh.exe'
+  if (shell === WINDOWS_GIT_BASH_SHELL) {
+    return 'git-bash'
   }
-  if (name !== '' && name !== 'powershell.exe' && name !== 'powershell') {
+  const name = shell
+    .replaceAll('\\', '/')
+    .split('/')
+    .pop()
+    ?.toLowerCase()
+    .replace(/\.exe$/, '')
+  if (name === 'pwsh' || name === 'cmd' || name === 'wsl') {
+    return `${name}.exe`
+  }
+  if (name !== '' && name !== 'powershell') {
     return null
   }
   const implementation = args.settings?.terminalWindowsPowerShellImplementation
@@ -64,15 +78,15 @@ export function describeLaunchHost(args: {
   /** The platform of the machine this Orca runs on. */
   hostPlatform: NodeJS.Platform
   paired: boolean
-  /** `spawnedWindowsPowerShell` on this machine, which a launch elsewhere does not use. */
-  windowsPowerShell?: WindowsPowerShell | null
+  /** `spawnedWindowsShell` on this machine, which a launch elsewhere does not use. */
+  windowsPaneShell?: WindowsPaneShell | null
 }): LaunchHost {
   const runsElsewhere = args.isRemote || args.paired
   return {
     paired: args.paired,
     provesAgentInFront: (runsElsewhere ? args.launchPlatform : args.hostPlatform) !== 'win32',
     takesLaunchFile: !args.paired && !(args.isRemote && args.launchPlatform === 'win32'),
-    windowsPowerShell:
-      runsElsewhere || args.launchPlatform !== 'win32' ? null : (args.windowsPowerShell ?? null)
+    windowsPaneShell:
+      runsElsewhere || args.launchPlatform !== 'win32' ? null : (args.windowsPaneShell ?? null)
   }
 }

src/shared/launch-prompt-carrier.test.ts

@@ -29,7 +29,7 @@ describe('the one launch-prompt decision every launch path builds through', () =
         paired: true,
         provesAgentInFront: true,
         takesLaunchFile: false,
-        windowsPowerShell: null
+        windowsPaneShell: null
       }
     })
     expect(short?.carry).toBe('on-line')
@@ -41,7 +41,7 @@ describe('the one launch-prompt decision every launch path builds through', () =
         paired: true,
         provesAgentInFront: true,
         takesLaunchFile: false,
-        windowsPowerShell: null
+        windowsPaneShell: null
       }
     })
     expect(long?.carry).toBe('paste-after-ready')

src/shared/launch-prompt-carry.test.ts

@@ -185,7 +185,7 @@ describe('a host that types the line raw', () => {
         paired: false,
         provesAgentInFront: false,
         takesLaunchFile: true,
-        windowsPowerShell: null
+        windowsPaneShell: null
       }
     }
     const prompt = 'fix the build\nthen run the tests'
@@ -225,7 +225,7 @@ describe('a host that types the line raw', () => {
         paired: true,
         provesAgentInFront: true,
         takesLaunchFile: false,
-        windowsPowerShell: null
+        windowsPaneShell: null
       }
     }
     expect(plan('claude', 'fix it', extra)?.carry).toBe('on-line')

src/shared/launch-prompt-carry.ts

@@ -169,9 +169,16 @@ export function carryLaunchPrompt<A extends CarriedPlanArgs, P extends { launchC
   if (readsEnv) {
     return { carry: 'on-line', plan }
   }
+  const paneShell = args.host.windowsPaneShell
+  // Why not for a WSL pane: it runs the distro's POSIX shell, which the host stages into.
   const windowsLine =
-    args.platform === 'win32'
-      ? windowsLaunchLineVerdict(text, plan.launchCommand, shell, args.host.windowsPowerShell)
+    args.platform === 'win32' && paneShell !== 'wsl.exe'
+      ? windowsLaunchLineVerdict(
+          text,
+          plan.launchCommand,
+          shell,
+          paneShell === 'powershell.exe' || paneShell === 'pwsh.exe' ? paneShell : null
+        )
       : 'exact'
   // Why #24257's typed budget: an older paired host may type the line raw, truncated past it.
   if (

src/shared/tui-agent-startup.test.ts

@@ -104,24 +104,37 @@ describe('tui agent startup plans', () => {
     expect(plan?.launchCommand).toBe('claude "fix ""quoted"" & "^%"PATH"^%""')
   })
 
-  it.each(['cmd', 'powershell'] as const)(
-    'never types a line break into %s: a multi-line prompt rides a launch file',
-    (shell) => {
-      const prompt = 'fix the build\r\n& echo PWNED\nthen run tests'
-      const plan = planLaunchForTest({
-        agent: 'claude',
-        prompt,
-        cmdOverrides: {},
-        platform: 'win32',
-        shell
-      })
+  it('never types a line break into cmd: a multi-line prompt rides a launch file', () => {
+    const prompt = 'fix the build\r\n& echo PWNED\nthen run tests'
+    const plan = planLaunchForTest({
+      agent: 'claude',
+      prompt,
+      cmdOverrides: {},
+      platform: 'win32',
+      shell: 'cmd'
+    })
 
-      expect(plan?.launchCommand).not.toMatch(/[\r\n]/)
-      expect(plan?.launchCommand).not.toContain('PWNED')
-      expect(plan?.launchFile).toMatchObject({ content: prompt })
-      expect(plan?.launchCommand).toContain(plan?.launchFile?.placeholder)
-    }
-  )
+    expect(plan?.launchCommand).not.toMatch(/[\r\n]/)
+    expect(plan?.launchCommand).not.toContain('PWNED')
+    expect(plan?.launchFile).toMatchObject({ content: prompt })
+    expect(plan?.launchCommand).toContain(plan?.launchFile?.placeholder)
+  })
+
+  // Why: PowerShell keeps a line break inside a single-quoted argument (measured), so `&` there is
+  // text, never a command; a CR before a line feed was not measured, so it is typed as main typed it.
+  it('keeps a PowerShell prompt with line breaks inside its one quoted argument', () => {
+    const prompt = 'fix the build\r\n& echo PWNED\nthen run tests'
+    const plan = planLaunchForTest({
+      agent: 'claude',
+      prompt,
+      cmdOverrides: {},
+      platform: 'win32',
+      shell: 'powershell'
+    })
+
+    expect(plan?.launchFile).toBeUndefined()
+    expect(plan?.launchCommand).toBe(`claude '${prompt}'`)
+  })
 
   it('keeps a multi-line prompt inline for a POSIX shell on a POSIX host, which stages it', () => {
     const plan = planLaunchForTest({

src/shared/windows-launch-line.test.ts

@@ -37,7 +37,7 @@ function windowsHost(windowsPowerShell: WindowsPowerShell | null) {
     isRemote: false,
     hostPlatform: 'win32',
     paired: false,
-    windowsPowerShell
+    windowsPaneShell: windowsPowerShell
   })
 }
 
@@ -132,29 +132,48 @@ describe('an agent.launch prompt on a Windows host, per measured shell', () => {
     )
   })
 
-  // Why: a typed carriage return is Enter (in cmd the rest runs as commands) and a Tab completes.
-  it.each<AgentStartupShell>(['cmd', 'powershell', 'posix'])(
-    'never types a Tab or a carriage return into %s',
-    (shell) => {
-      const planned = (paste: 'once-agent-runs' | 'when-host-proves-agent') =>
-        planLaunchPrompt({
-          agent: 'claude',
-          prompt: 'before\tmiddle\r& echo PWNED',
-          cmdOverrides: {},
-          platform: 'win32',
-          shell,
-          host: describeLaunchHost({
-            launchPlatform: 'win32',
-            isRemote: false,
-            hostPlatform: 'win32',
-            paired: false
-          }),
-          paste
-        })?.carry
-      expect(planned('once-agent-runs')).toBe('paste-after-ready')
-      expect(planned('when-host-proves-agent')).toBe('launch-file')
+  // Why per shell (stack QA ptab/pcr): cmd and Git Bash read a Tab or carriage return as a key
+  // (completion, or Enter, which in cmd runs the rest as commands); both PowerShells carried them.
+  it.each<[AgentStartupShell, 'ptab' | 'pcr', 'on-line' | 'launch-file']>([
+    ['cmd', 'ptab', 'launch-file'],
+    ['cmd', 'pcr', 'launch-file'],
+    ['posix', 'ptab', 'launch-file'],
+    ['posix', 'pcr', 'launch-file'],
+    ['powershell', 'ptab', 'on-line'],
+    ['powershell', 'pcr', 'on-line']
+  ])('types %s %s only where the shell carried it: %s', (shell, row, expected) => {
+    const prompt =
+      row === 'ptab'
+        ? 'QA-STACK PTAB one line with a\ttab inside, inert, do not run any command.'
+        : 'QA-STACK PCR one line with a bare\rCR inside, inert, do not run any command.'
+    for (const windowsPowerShell of ['powershell.exe', 'pwsh.exe'] as const) {
+      const planned = planLaunchPrompt({
+        agent: 'claude',
+        prompt,
+        cmdOverrides: {},
+        platform: 'win32',
+        shell,
+        host: windowsHost(windowsPowerShell),
+        paste: 'when-host-proves-agent'
+      })
+      expect(planned?.carry).toBe(expected)
     }
-  )
+  })
+
+  it('leaves another control byte, never measured, to main’s delivery', () => {
+    const planned = (paste: 'once-agent-runs' | 'when-host-proves-agent') =>
+      planLaunchPrompt({
+        agent: 'claude',
+        prompt: 'before\x1bafter',
+        cmdOverrides: {},
+        platform: 'win32',
+        shell: 'powershell',
+        host: windowsHost('pwsh.exe'),
+        paste
+      })?.carry
+    expect(planned('once-agent-runs')).toBe('paste-after-ready')
+    expect(planned('when-host-proves-agent')).toBe('on-line')
+  })
 
   // Why: an AI button's prompt was pasted on main, so only a line measured exact replaces that
   // paste; measured damage and the unmeasured both keep main's paste.

src/shared/windows-launch-line.ts

@@ -28,16 +28,20 @@ const WINDOWS_POSIX_LINE_DAMAGED_CHARS = 20_551
 
 const encoder = new TextEncoder()
 
-/** A control byte other than a line feed: every Windows line editor reads it as a key (a carriage
- *  return is Enter, which in cmd runs the rest as commands; Tab completes), so the bytes change. */
-function hasKeyByte(line: string): boolean {
+/** Control bytes other than a line feed: Tab and carriage return were measured, the rest not. */
+function keyBytes(line: string): { tabOrReturn: boolean; unmeasured: boolean } {
+  let tabOrReturn = false
+  let unmeasured = false
   for (let i = 0; i < line.length; i += 1) {
     const code = line.charCodeAt(i)
-    if ((code < 0x20 && code !== 0x0a) || code === 0x7f) {
-      return true
+    // Measured: a Tab and a bare carriage return; a CR before a line feed was not.
+    if (code === 0x09 || (code === 0x0d && line.charCodeAt(i + 1) !== 0x0a)) {
+      tabOrReturn = true
+    } else if ((code < 0x20 && code !== 0x0a) || code === 0x7f) {
+      unmeasured = true
     }
   }
-  return false
+  return { tabOrReturn, unmeasured }
 }
 
 /** An agent spelled as a `.cmd`/`.bat` shim, whose cmd.exe re-reads its arguments. A bare name
@@ -70,6 +74,10 @@ function shellVerdict(line: string, shell: AgentStartupShell): WindowsLineVerdic
   return line.length >= WINDOWS_POSIX_LINE_DAMAGED_CHARS ? 'damaged' : 'uncertain'
 }
 
+function withUnmeasuredKeys(verdict: WindowsLineVerdict, unmeasured: boolean): WindowsLineVerdict {
+  return unmeasured && verdict === 'exact' ? 'uncertain' : verdict
+}
+
 export function windowsLaunchLineVerdict(
   prompt: string,
   line: string,
@@ -77,10 +85,13 @@ export function windowsLaunchLineVerdict(
   /** The PowerShell the pane is spawned as (`LaunchHost.windowsPowerShell`), when known. */
   windowsPowerShell: WindowsPowerShell | null
 ): WindowsLineVerdict {
-  if (hasKeyByte(line)) {
+  const keys = keyBytes(line)
+  // Measured: cmd and Git Bash read a Tab or carriage return as a key (completion, or Enter, which
+  // in cmd runs the rest as commands); both PowerShells carried them exactly.
+  if (keys.tabOrReturn && shell !== 'powershell') {
     return 'damaged'
   }
-  const verdict = shellVerdict(line, shell)
+  const verdict = withUnmeasuredKeys(shellVerdict(line, shell), keys.unmeasured)
   const legacyArgsDamage = prompt.includes('"') || prompt.endsWith('\\')
   if (shell === 'cmd' || !launchesThroughCmdShim(line)) {
     if (shell !== 'powershell' || verdict !== 'exact' || !legacyArgsDamage) {

src/shared/windows-shell-prompt-damage.test.ts

@@ -99,7 +99,7 @@ describe('a prompt a Windows shell would damage on the launch line', () => {
         paired: true,
         provesAgentInFront: false,
         takesLaunchFile: false,
-        windowsPowerShell: null
+        windowsPaneShell: null
       }
     })
     expect(startup?.launchFile).toBeUndefined()