From 91d3ed6c5acf7e7af8f3c300a5ca1f5a73c64526 Mon Sep 17 00:00:00 2001
From: Huanqi Cao <caohuanqi@deepseek.com>
Date: Sat, 8 Aug 2026 14:32:01 +0800
Subject: [PATCH] =?UTF-8?q?fix(sandbox):=20address=20the=20ACL=20backend?=
 =?UTF-8?q?=20review=20findings=20=E2=80=94=20quoting,=20DACL=20merge+lock?=
 =?UTF-8?q?,=20failure=20paths?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

quoteArg doubles end-of-string backslashes (real CommandLineToArgvW round-trip test; first-token exemption noted); grantWrite merges into the current DACL instead of replacing it, and both grant/revoke hold a LockFileEx per-path lock under GetTempPathW/dsh-acl-locks (koffi crashes on NULL lpOverlapped — a zeroed OVERLAPPED is used); GRANT_MASK gains DELETE|FILE_DELETE_CHILD (never WRITE_DAC/WRITE_OWNER) though the win32 26200 second check only constrains the WRITE bit; failure paths close all handles (CreateProcessAsUserW pipe set, ResumeThread thread/process/job) with stub-api tests; getTempPathW refuses undersized buffers; drainPipe backs off; runner.spec pwshAvailable uses the resolvePwshPath probe; NTSTATUS exit codes mirror bit-exact (verified end-to-end); WinLocalSid JSDoc re-attributed to WinLocalLogonSid. All gates green: 42 passed/2 skipped, typecheck, oxlint, 0 clones, constraints, knip.
---
 .../sandbox/sandbox-windows-acl/package.json  |   1 +
 .../sandbox/sandbox-windows-acl/src/acl.ts    | 206 +++++++++++----
 .../sandbox/sandbox-windows-acl/src/ffi.ts    |  56 +++++
 .../sandbox/sandbox-windows-acl/src/index.ts  |   9 +-
 .../sandbox/sandbox-windows-acl/src/runner.ts |   9 +
 .../sandbox/sandbox-windows-acl/src/spawn.ts  |  46 +++-
 .../sandbox-windows-acl/src/win32-abi.ts      |  64 ++++-
 .../sandbox-windows-acl/tests/acl.spec.ts     | 234 ++++++++++++++++++
 .../tests/failure-paths.spec.ts               | 112 +++++++++
 .../sandbox-windows-acl/tests/quote.spec.ts   |  88 +++++++
 .../sandbox-windows-acl/tests/runner.spec.ts  |  37 ++-
 .../sandbox-windows-acl/verify/abi-probe.cpp  |  23 +-
 pnpm-lock.yaml                                |   3 +
 13 files changed, 805 insertions(+), 83 deletions(-)
 create mode 100644 packages/sandbox/sandbox-windows-acl/tests/acl.spec.ts
 create mode 100644 packages/sandbox/sandbox-windows-acl/tests/failure-paths.spec.ts
 create mode 100644 packages/sandbox/sandbox-windows-acl/tests/quote.spec.ts

diff --git a/packages/sandbox/sandbox-windows-acl/package.json b/packages/sandbox/sandbox-windows-acl/package.json
index 3f4d6cc065..2f13b71296 100644
--- a/packages/sandbox/sandbox-windows-acl/package.json
+++ b/packages/sandbox/sandbox-windows-acl/package.json
@@ -38,6 +38,7 @@
   },
   "devDependencies": {
     "@deepseek-ai/dsh-invariants": "workspace:^",
+    "@deepseek-ai/dsh-pwsh-local": "workspace:^",
     "@deepseek-ai/dsh-sandbox-local": "workspace:^",
     "cordis": "^4.0.0-rc.7"
   }
diff --git a/packages/sandbox/sandbox-windows-acl/src/acl.ts b/packages/sandbox/sandbox-windows-acl/src/acl.ts
index 44020ae0c3..7700474d5f 100644
--- a/packages/sandbox/sandbox-windows-acl/src/acl.ts
+++ b/packages/sandbox/sandbox-windows-acl/src/acl.ts
@@ -4,10 +4,19 @@
  * the failure handling the POC lacks). Every API call is checked and every
  * failure is reported with the API name, the exact Win32 code, the formatted
  * system text, and the affected path.
+ *
+ * Concurrency: grants are read-merge-write against the directory's CURRENT
+ * DACL, and the whole get-merge-set sequence runs under a per-path exclusive
+ * LockFileEx lock (see {@link withPathLock}) so concurrent sandbox instances
+ * cannot clobber each other's ACEs.
  * @module @deepseek-ai/dsh-sandbox-windows-acl/acl
  */
 
-import { allocPtrSlot, decodePtr, isNullPtr, ptrAddress, throwLastError, throwWin32 } from './ffi.ts'
+import { createHash } from 'node:crypto'
+import { mkdirSync } from 'node:fs'
+import { dirname, join } from 'node:path'
+
+import { allocOverlapped, allocPtrSlot, decodePtr, getTempPath, isInvalidHandle, isNullPtr, ptrAddress, throwLastError, throwWin32 } from './ffi.ts'
 import type { NativePtr, Win32Bindings } from './ffi.ts'
 import * as abi from './win32-abi.ts'
 
@@ -18,7 +27,7 @@ import * as abi from './win32-abi.ts'
  * `permissions` is the access mask; the POC passes 0 for REVOKE_ACCESS, which
  * removes every ACE for the trustee.
  */
-function buildExplicitAccess(sidPtr: NativePtr, mode: number, permissions: number): Buffer {
+export function buildExplicitAccess(sidPtr: NativePtr, mode: number, permissions: number): Buffer {
   const entry = Buffer.alloc(abi.EXPLICIT_ACCESS_W_SIZE)
   entry.writeUInt32LE(permissions, 0) // grfAccessPermissions
   entry.writeUInt32LE(mode, 4) // grfAccessMode
@@ -31,47 +40,82 @@ function buildExplicitAccess(sidPtr: NativePtr, mode: number, permissions: numbe
 }
 
 /**
- * Grant `FILE_GENERIC_WRITE & ~READ_CONTROL` (displays as "Write") to the
- * orphan SID on `path`, inheriting to subcontainers and objects. The directory
- * must be owned by the caller (owner implicit WRITE_DAC) — same precondition
- * as the POC.
+ * One lock file per protected path: `<GetTempPathW()>\dsh-acl-locks\<first 16
+ * hex of sha256(lowercased path)>.lock`. The lock root derives from
+ * GetTempPathW (never from runner argv or DSH_HOME), and the lowercasing
+ * maps Windows's case-insensitive path spellings onto one lock.
  * @param api - the binding table.
- * @param path - the directory whose DACL gains the grant (the workspace or temp root).
- * @param sidPtr - the orphan write SID the ACE names.
+ * @param path - the protected directory (absolute).
+ * @returns the lock file path for that directory.
  */
-export function grantWrite(api: Win32Bindings, path: string, sidPtr: NativePtr): void {
-  const newAclSlot = allocPtrSlot()
-  const mergeResult = api.setEntriesInAclW(1, buildExplicitAccess(sidPtr, abi.GRANT_ACCESS, abi.GRANT_MASK), null, newAclSlot)
-  if (mergeResult !== abi.ERROR_SUCCESS) throwWin32(api, 'SetEntriesInAclW', mergeResult, path)
-  const newAcl = decodePtr(newAclSlot)
-  if (newAcl === null) throwWin32(api, 'SetEntriesInAclW', api.getLastError(), `null ACL for ${path}`)
-
-  const applyResult = api.setNamedSecurityInfoW(
-    path, abi.SE_FILE_OBJECT, abi.DACL_SECURITY_INFORMATION,
-    null, null, newAcl, null,
-  )
-  // Free the LocalAlloc'd ACL before any throw; capture both outcomes first.
-  const freed = api.localFree(newAcl)
-  if (applyResult !== abi.ERROR_SUCCESS) throwWin32(api, 'SetNamedSecurityInfoW', applyResult, path)
-  if (!isNullPtr(freed)) throwLastError(api, 'LocalFree', `grantWrite(${path})`)
+export function lockFilePath(api: Win32Bindings, path: string): string {
+  const digest = createHash('sha256').update(path.toLowerCase()).digest('hex').slice(0, 16)
+  return join(getTempPath(api), 'dsh-acl-locks', `${digest}.lock`)
 }
 
 /**
- * Remove every ACE for the orphan SID from the directory DACL (REVOKE_ACCESS
- * merge — other entries are preserved). Returns whether an ACE removal was
- * attempted (false when the directory carries no DACL at all).
- *
- * Allocation contract (the POC's RevokeAccess, minus its missing checks):
- * GetNamedSecurityInfoW returns the DACL pointer INSIDE the security
- * descriptor allocation — only the descriptor may be LocalFree'd, and it must
- * not be freed before SetEntriesInAclW has consumed the ACL. Freeing the ACL
- * pointer itself corrupts the heap (verified the hard way).
+ * Run `action` holding the per-path exclusive lock: CreateFileW
+ * (OPEN_ALWAYS, shared read/write but NOT delete — a deletable lock file
+ * could be removed and recreated under the holder, letting two processes
+ * hold "the same" lock), then a one-byte LockFileEx
+ * (LOCKFILE_EXCLUSIVE_LOCK, zeroed OVERLAPPED = lock from offset 0 on the
+ * synchronous handle — see allocOverlapped for why not NULL), then
+ * UnlockFileEx + CloseHandle. Fail-closed: open/lock/unlock/close failures
+ * throw like every other Win32 call in this package; an `action` failure
+ * still unlocks (best-effort) and rethrows the original error.
  * @param api - the binding table.
- * @param path - the directory whose DACL loses the orphan-SID ACEs.
- * @param sidPtr - the orphan write SID whose ACEs are removed.
- * @returns whether an ACE removal was attempted (false when the directory carries no DACL at all).
+ * @param path - the protected directory (absolute).
+ * @param action - the get-merge-set sequence to serialize.
+ * @returns the action's result.
  */
-export function revokeWrite(api: Win32Bindings, path: string, sidPtr: NativePtr): boolean {
+export function withPathLock<T>(api: Win32Bindings, path: string, action: () => T): T {
+  const lockPath = lockFilePath(api, path)
+  mkdirSync(dirname(lockPath), { recursive: true })
+  const handle = api.createFileW(
+    lockPath,
+    abi.GENERIC_READ | abi.GENERIC_WRITE,
+    abi.FILE_SHARE_READ | abi.FILE_SHARE_WRITE,
+    null, abi.OPEN_ALWAYS, 0, null,
+  )
+  if (isInvalidHandle(handle)) throwLastError(api, 'CreateFileW', lockPath)
+  const overlapped = allocOverlapped() // stays zeroed: offset 0, hEvent NULL
+  if (api.lockFileEx(handle, abi.LOCKFILE_EXCLUSIVE_LOCK, 0, 1, 0, overlapped) === 0) {
+    const win32Code = api.getLastError()
+    api.closeHandle(handle) // best-effort on the lock-failure path
+    throwWin32(api, 'LockFileEx', win32Code, lockPath)
+  }
+
+  let result: T
+  try {
+    result = action()
+  } catch (error) {
+    // Best-effort release on the action-failure path: cleanup failures must
+    // not mask the action's error.
+    api.unlockFileEx(handle, 0, 1, 0, overlapped)
+    api.closeHandle(handle)
+    throw error
+  }
+  if (api.unlockFileEx(handle, 0, 1, 0, overlapped) === 0) {
+    const win32Code = api.getLastError()
+    api.closeHandle(handle) // best-effort on the unlock-failure path
+    throwWin32(api, 'UnlockFileEx', win32Code, lockPath)
+  }
+  if (api.closeHandle(handle) === 0) throwLastError(api, 'CloseHandle', `lock file ${lockPath}`)
+  return result
+}
+
+/**
+ * Read the directory's current explicit DACL via GetNamedSecurityInfoW.
+ * Allocation contract (the POC's RevokeAccess, minus its missing checks): the
+ * returned ACL pointer sits INSIDE the security descriptor allocation — only
+ * the descriptor may be LocalFree'd, and it must not be freed before
+ * SetEntriesInAclW has consumed the ACL. Freeing the ACL pointer itself
+ * corrupts the heap (verified the hard way).
+ * @param api - the binding table.
+ * @param path - the directory whose DACL is read.
+ * @returns the current explicit DACL (null when the directory carries none) and its owning descriptor.
+ */
+function readCurrentDacl(api: Win32Bindings, path: string): { oldAcl: NativePtr | null; descriptor: NativePtr | null } {
   const ownerSlot = allocPtrSlot()
   const groupSlot = allocPtrSlot()
   const daclSlot = allocPtrSlot()
@@ -82,27 +126,39 @@ export function revokeWrite(api: Win32Bindings, path: string, sidPtr: NativePtr)
     ownerSlot, groupSlot, daclSlot, saclSlot, descriptorSlot,
   )
   if (readResult !== abi.ERROR_SUCCESS) throwWin32(api, 'GetNamedSecurityInfoW', readResult, path)
-  const oldAcl = decodePtr(daclSlot)
-  const descriptor = decodePtr(descriptorSlot)
-
-  if (oldAcl === null) {
-    if (descriptor !== null) {
-      const freed = api.localFree(descriptor)
-      if (!isNullPtr(freed)) throwLastError(api, 'LocalFree', `revokeWrite(${path}) descriptor`)
-    }
-    return false
-  }
+  return { oldAcl: decodePtr(daclSlot), descriptor: decodePtr(descriptorSlot) }
+}
 
+/**
+ * Shared tail of grantWrite and revokeWrite: merge `entry` into `oldAcl`
+ * (null = no explicit DACL yet; SetEntriesInAclW builds one from scratch),
+ * free the descriptor before applying the merged ACL, apply it, then free the
+ * merged ACL — checking every call and reporting with the caller's label.
+ * @param api - the binding table.
+ * @param path - the directory the DACL edit applies to.
+ * @param entry - the EXPLICIT_ACCESS_W to merge (grant or revoke).
+ * @param oldAcl - the current explicit DACL (from {@link readCurrentDacl}).
+ * @param descriptor - the descriptor allocation owning `oldAcl`.
+ * @param label - the caller's name for error details.
+ */
+function mergeAndApply(
+  api: Win32Bindings,
+  path: string,
+  entry: Buffer,
+  oldAcl: NativePtr | null,
+  descriptor: NativePtr | null,
+  label: string,
+): void {
   const newAclSlot = allocPtrSlot()
-  const mergeResult = api.setEntriesInAclW(1, buildExplicitAccess(sidPtr, abi.REVOKE_ACCESS, 0), oldAcl, newAclSlot)
+  const mergeResult = api.setEntriesInAclW(1, entry, oldAcl, newAclSlot)
   if (mergeResult !== abi.ERROR_SUCCESS) {
     if (descriptor !== null) api.localFree(descriptor) // frees the ACL block too
-    throwWin32(api, 'SetEntriesInAclW', mergeResult, `revokeWrite(${path})`)
+    throwWin32(api, 'SetEntriesInAclW', mergeResult, `${label}(${path})`)
   }
   const newAcl = decodePtr(newAclSlot)
   if (newAcl === null) {
     if (descriptor !== null) api.localFree(descriptor)
-    throwWin32(api, 'SetEntriesInAclW', api.getLastError(), `revokeWrite(${path}): null new ACL`)
+    throwWin32(api, 'SetEntriesInAclW', api.getLastError(), `${label}(${path}): null new ACL`)
   }
 
   // The descriptor block (oldAcl included) is dead after the merge — free it
@@ -113,8 +169,52 @@ export function revokeWrite(api: Win32Bindings, path: string, sidPtr: NativePtr)
     null, null, newAcl, null,
   )
   const freedNew = api.localFree(newAcl)
-  if (applyResult !== abi.ERROR_SUCCESS) throwWin32(api, 'SetNamedSecurityInfoW', applyResult, `revokeWrite(${path})`)
-  if (freedDescriptor !== null && !isNullPtr(freedDescriptor)) throwLastError(api, 'LocalFree', `revokeWrite(${path}) descriptor`)
-  if (!isNullPtr(freedNew)) throwLastError(api, 'LocalFree', `revokeWrite(${path}) new ACL`)
-  return true
+  if (applyResult !== abi.ERROR_SUCCESS) throwWin32(api, 'SetNamedSecurityInfoW', applyResult, `${label}(${path})`)
+  if (freedDescriptor !== null && !isNullPtr(freedDescriptor)) throwLastError(api, 'LocalFree', `${label}(${path}) descriptor`)
+  if (!isNullPtr(freedNew)) throwLastError(api, 'LocalFree', `${label}(${path}) new ACL`)
+}
+
+/**
+ * Grant `GRANT_MASK` (Write+Delete, displays as "Modify") to the orphan SID
+ * on `path`, inheriting to subcontainers and objects. Read-merge-write: the
+ * new ACE merges into the directory's CURRENT explicit DACL (same shape as
+ * {@link revokeWrite}), so pre-existing explicit ACEs survive. Runs under the
+ * per-path lock. The directory must be owned by the caller (owner implicit
+ * WRITE_DAC) — same precondition as the POC.
+ * @param api - the binding table.
+ * @param path - the directory whose DACL gains the grant (the workspace or temp root).
+ * @param sidPtr - the orphan write SID the ACE names.
+ */
+export function grantWrite(api: Win32Bindings, path: string, sidPtr: NativePtr): void {
+  withPathLock(api, path, () => {
+    const { oldAcl, descriptor } = readCurrentDacl(api, path)
+    mergeAndApply(api, path, buildExplicitAccess(sidPtr, abi.GRANT_ACCESS, abi.GRANT_MASK), oldAcl, descriptor, 'grantWrite')
+  })
+}
+
+/**
+ * Remove every ACE for the orphan SID from the directory DACL (REVOKE_ACCESS
+ * merge — other entries are preserved). Returns whether an ACE removal was
+ * attempted (false when the directory carries no DACL at all).
+ *
+ * Runs under the per-path lock (the whole get-merge-set sequence); the
+ * descriptor/ACL allocation contract lives on {@link readCurrentDacl}.
+ * @param api - the binding table.
+ * @param path - the directory whose DACL loses the orphan-SID ACEs.
+ * @param sidPtr - the orphan write SID whose ACEs are removed.
+ * @returns whether an ACE removal was attempted (false when the directory carries no DACL at all).
+ */
+export function revokeWrite(api: Win32Bindings, path: string, sidPtr: NativePtr): boolean {
+  return withPathLock(api, path, () => {
+    const { oldAcl, descriptor } = readCurrentDacl(api, path)
+    if (oldAcl === null) {
+      if (descriptor !== null) {
+        const freed = api.localFree(descriptor)
+        if (!isNullPtr(freed)) throwLastError(api, 'LocalFree', `revokeWrite(${path}) descriptor`)
+      }
+      return false
+    }
+    mergeAndApply(api, path, buildExplicitAccess(sidPtr, abi.REVOKE_ACCESS, 0), oldAcl, descriptor, 'revokeWrite')
+    return true
+  })
 }
diff --git a/packages/sandbox/sandbox-windows-acl/src/ffi.ts b/packages/sandbox/sandbox-windows-acl/src/ffi.ts
index 6d778f7b11..1d9665a8fc 100644
--- a/packages/sandbox/sandbox-windows-acl/src/ffi.ts
+++ b/packages/sandbox/sandbox-windows-acl/src/ffi.ts
@@ -26,6 +26,17 @@ export function isNullPtr(value: NativePtr | null | undefined): value is null |
   return value === null || value === undefined || (value as bigint) === 0n
 }
 
+/**
+ * True for CreateFileW's INVALID_HANDLE_VALUE failure marker (-1, which
+ * koffi hands back as the unsigned 64-bit all-ones pointer).
+ * @param handle - the handle CreateFileW returned.
+ * @returns whether the handle signals failure.
+ */
+export function isInvalidHandle(handle: NativePtr | null | undefined): boolean {
+  if (isNullPtr(handle)) return true
+  return (handle as bigint) === 0xFFFFFFFFFFFFFFFFn || (handle as bigint) === -1n
+}
+
 type Ptr = ReturnType<typeof koffi.pointer>
 
 /** Field subset written into a zeroed STARTUPINFOW (layout verified: size 104). */
@@ -86,6 +97,12 @@ export interface Win32Bindings {
   ): number
   // ---- environment / io ----------------------------------------------------
   getTempPathW(length: number, buffer: Buffer): number
+  createFileW(
+    fileName: string, desiredAccess: number, shareMode: number, attributes: null,
+    creationDisposition: number, flagsAndAttributes: number, templateFile: null,
+  ): NativePtr
+  lockFileEx(file: NativePtr, flags: number, reserved: number, bytesLow: number, bytesHigh: number, overlapped: NativePtr): number
+  unlockFileEx(file: NativePtr, reserved: number, bytesLow: number, bytesHigh: number, overlapped: NativePtr): number
   createPipe(readHandle: NativePtr, writeHandle: NativePtr, attributes: null, size: number): number
   setHandleInformation(handle: NativePtr, mask: number, flags: number): number
   createProcessAsUserW(
@@ -231,6 +248,18 @@ export function allocBytes(length: number): NativePtr {
   return value as NativePtr
 }
 
+/**
+ * Allocate one zeroed OVERLAPPED (32 bytes on x64: Internal@0, InternalHigh@8,
+ * Offset@16, OffsetHigh@20, hEvent@24). LockFileEx/UnlockFileEx receive this
+ * instead of a NULL lpOverlapped: koffi 3.1.1 crashes on NULL there, and a
+ * zeroed OVERLAPPED on a synchronous file handle is the documented equivalent
+ * (the byte range locks from offset 0, hEvent stays NULL).
+ * @returns the zeroed block pointer.
+ */
+export function allocOverlapped(): NativePtr {
+  return allocBytes(32)
+}
+
 /**
  * Decode a pointer VALUE stored in memory at `buffer[offset]` (e.g. TOKEN_GROUPS entries).
  * @param buffer - the buffer holding the pointer value.
@@ -313,6 +342,14 @@ function bindings(): Win32Bindings {
     setNamedSecurityInfoW: bind(advapi32, 'SetNamedSecurityInfoW', 'uint32', ['str16', 'int', 'uint32', PVOID, PVOID, PVOID, PVOID]),
     getNamedSecurityInfoW: bind(advapi32, 'GetNamedSecurityInfoW', 'uint32', ['str16', 'int', 'uint32', PPVOID, PPVOID, PPVOID, PPVOID, PPVOID]),
     getTempPathW: bind(kernel32, 'GetTempPathW', 'uint32', ['uint32', PVOID]),
+    // fileapi.h line ~64: HANDLE CreateFileW(LPCWSTR, DWORD, DWORD,
+    // LPSECURITY_ATTRIBUTES, DWORD, DWORD, HANDLE).
+    createFileW: bind(kernel32, 'CreateFileW', PVOID, ['str16', 'uint32', 'uint32', PVOID, 'uint32', 'uint32', PVOID]),
+    // fileapi.h lines ~177/~185: BOOL LockFileEx(HANDLE, DWORD, DWORD, DWORD,
+    // DWORD, LPOVERLAPPED); BOOL UnlockFileEx(HANDLE, DWORD, DWORD, DWORD,
+    // LPOVERLAPPED). lpOverlapped is NULL for synchronous locking.
+    lockFileEx: bind(kernel32, 'LockFileEx', 'int', [PVOID, 'uint32', 'uint32', 'uint32', 'uint32', PVOID]),
+    unlockFileEx: bind(kernel32, 'UnlockFileEx', 'int', [PVOID, 'uint32', 'uint32', 'uint32', PVOID]),
     createPipe: bind(kernel32, 'CreatePipe', 'int', [PPVOID, PPVOID, PVOID, 'uint32']),
     setHandleInformation: bind(kernel32, 'SetHandleInformation', 'int', [PVOID, 'uint32', 'uint32']),
     createProcessAsUserW: bind(advapi32, 'CreateProcessAsUserW', 'int', [
@@ -357,6 +394,25 @@ export function errorText(api: Win32Bindings, win32Code: number): string {
   return buffer.subarray(0, length * 2).toString('utf16le').trim()
 }
 
+/**
+ * Read the process temp directory via GetTempPathW (fileapi.h line ~188).
+ * Defensive against an overlong system temp path: GetTempPathW reports the
+ * REQUIRED length (including NUL) without writing the buffer when it is too
+ * small, so a reported length beyond the buffer's capacity means the buffer
+ * was never filled and must not be decoded.
+ * @param api - the binding table.
+ * @returns the NUL-terminated temp path decoded as a string.
+ */
+export function getTempPath(api: Win32Bindings): string {
+  const buffer = Buffer.alloc((abi.MAX_PATH + 1) * 2)
+  const length = api.getTempPathW(buffer.length / 2, buffer)
+  if (length === 0) throwLastError(api, 'GetTempPathW')
+  if (length > buffer.length / 2) {
+    throw new Win32Error('GetTempPathW', abi.ERROR_INSUFFICIENT_BUFFER, `required ${length} chars exceed the ${buffer.length / 2}-char buffer; nothing was written`)
+  }
+  return buffer.subarray(0, length * 2).toString('utf16le')
+}
+
 /**
  * Throw a Win32Error for a BOOL-style API failure. MUST be called immediately
  * after the failed call so GetLastError is not clobbered by other Win32 calls.
diff --git a/packages/sandbox/sandbox-windows-acl/src/index.ts b/packages/sandbox/sandbox-windows-acl/src/index.ts
index f597ebbc72..e312a40e09 100644
--- a/packages/sandbox/sandbox-windows-acl/src/index.ts
+++ b/packages/sandbox/sandbox-windows-acl/src/index.ts
@@ -29,7 +29,7 @@ import { resolve } from 'node:path'
 
 import { grantWrite, revokeWrite } from './acl.ts'
 import { Win32Error } from './errors.ts'
-import { allocPtrSlot, decodePtr, isNullPtr, throwLastError, win32 } from './ffi.ts'
+import { allocPtrSlot, decodePtr, getTempPath, isNullPtr, throwLastError, win32 } from './ffi.ts'
 import type { NativePtr, Win32Bindings } from './ffi.ts'
 import { drainPipe, spawnSandboxed, spawnSandboxedInherited, waitForExit } from './spawn.ts'
 import { createRestrictedToken, findLogonSid, makeWellKnownSid, openCurrentProcessToken } from './token.ts'
@@ -88,13 +88,6 @@ function randomWriteSid(): string {
   return `S-1-4-${randomInt(1, 2 ** 30)}-${randomInt(1, 2 ** 30)}`
 }
 
-function getTempPath(api: Win32Bindings): string {
-  const buffer = Buffer.alloc((abi.MAX_PATH + 1) * 2)
-  const length = api.getTempPathW(buffer.length / 2, buffer)
-  if (length === 0) throwLastError(api, 'GetTempPathW')
-  return buffer.subarray(0, length * 2).toString('utf16le')
-}
-
 /**
  * One write-restricted sandbox instance: token + orphan-SID grants + spawn.
  * `init()` is fail-closed — any Win32 failure revokes whatever was granted
diff --git a/packages/sandbox/sandbox-windows-acl/src/runner.ts b/packages/sandbox/sandbox-windows-acl/src/runner.ts
index 02fd416f7f..578a615f84 100644
--- a/packages/sandbox/sandbox-windows-acl/src/runner.ts
+++ b/packages/sandbox/sandbox-windows-acl/src/runner.ts
@@ -124,6 +124,15 @@ async function main(): Promise<number> {
 
 main().then(
   (exitCode) => {
+    // Exit-code mirroring is full-width on Windows, verified empirically on
+    // this machine (Windows 11 build 26200, Node 24): a child that exits
+    // with the NTSTATUS 0xC0000005 (STATUS_ACCESS_VIOLATION) is read back
+    // by GetExitCodeProcess as the uint32 3221225477, and after
+    // process.exitCode = 3221225477 the parent observes exactly
+    // 3221225477 (spawnSync status). PowerShell's $LASTEXITCODE and cmd
+    // print the signed view (-1073741819), but no truncation or masking
+    // happens anywhere in the chain — the mirror contract holds for the
+    // full 32-bit range, so no re-mapping is needed.
     process.exitCode = exitCode
   },
   (error: unknown) => {
diff --git a/packages/sandbox/sandbox-windows-acl/src/spawn.ts b/packages/sandbox/sandbox-windows-acl/src/spawn.ts
index d9c7c70564..9c0436f29f 100644
--- a/packages/sandbox/sandbox-windows-acl/src/spawn.ts
+++ b/packages/sandbox/sandbox-windows-acl/src/spawn.ts
@@ -14,9 +14,12 @@ import type { NativePtr, Win32Bindings } from './ffi.ts'
 import * as abi from './win32-abi.ts'
 
 /**
- * Quote one argument per the CommandLineToArgvW parsing rules (backslash
- * escaping only before quotes; a trailing backslash before the closing quote
- * is doubled).
+ * Quote one argument per the CommandLineToArgvW parsing rules: backslashes
+ * are doubled only before a quote character — including the closing quote
+ * this function appends, so a trailing backslash run is doubled as well
+ * (otherwise an odd run would escape the closing quote into a literal
+ * character and corrupt the rest of the command line). Mirrors the CRT
+ * ArgvQuote behavior Microsoft documents for command-line arguments.
  * @param argument - one argv entry to quote.
  * @returns the quoted entry (bare when quoting is unnecessary).
  */
@@ -30,10 +33,13 @@ export function quoteArg(argument: string): string {
       backslashes++
       index++
     }
-    if (index < argument.length && argument.charAt(index) === '"') {
+    if (index === argument.length) {
+      // Trailing backslash run: doubled so it cannot escape the closing quote.
+      quoted += '\\'.repeat(backslashes * 2)
+    } else if (argument.charAt(index) === '"') {
       quoted += '\\'.repeat(backslashes * 2 + 1) + '"'
     } else {
-      quoted += '\\'.repeat(backslashes) + (index < argument.length ? argument.charAt(index) : '')
+      quoted += '\\'.repeat(backslashes) + argument.charAt(index)
     }
   }
   return quoted + '"'
@@ -119,8 +125,19 @@ export function spawnSandboxed(
     null, options.cwd,
     startupInfo, processInfo,
   )
-  // Capture the failure before CloseHandle calls clobber GetLastError.
-  if (created === 0) throwLastError(api, 'CreateProcessAsUserW', `command: ${options.command}, cwd: ${options.cwd}`)
+  // Capture the failure before CloseHandle calls clobber GetLastError, then
+  // close every pipe handle created so far — the six-close contract this test
+  // surface pins (tests/failure-paths.spec.ts).
+  if (created === 0) {
+    const win32Code = api.getLastError()
+    api.closeHandle(stdIn.read)
+    api.closeHandle(stdIn.write)
+    api.closeHandle(stdOut.read)
+    api.closeHandle(stdOut.write)
+    api.closeHandle(stdErr.read)
+    api.closeHandle(stdErr.write)
+    throwWin32(api, 'CreateProcessAsUserW', win32Code, `command: ${options.command}, cwd: ${options.cwd}`)
+  }
 
   const info = decodeProcessInfo(processInfo)
   const processHandle = info.hProcess
@@ -172,7 +189,9 @@ export async function drainPipe(api: Win32Bindings, handle: NativePtr): Promise<
       }
       chunks.push(chunk.subarray(0, decodeUint32(readSlot)))
     }
-    await new Promise<void>(resolve => setImmediate(resolve))
+    // Small backoff instead of setImmediate: a bare next-tick would busy-poll
+    // the pipe at full event-loop speed while the child produces no output.
+    await new Promise<void>(resolve => setTimeout(resolve, 1))
   }
   api.closeHandle(handle)
   return Buffer.concat(chunks)
@@ -314,7 +333,16 @@ export function spawnSandboxedInherited(
     api.closeHandle(job)
     throwWin32(api, 'AssignProcessToJobObject', win32Code, `pid ${info.dwProcessId}`)
   }
-  if (api.resumeThread(threadHandle) === 0xFFFFFFFF) throwLastError(api, 'ResumeThread', `pid ${info.dwProcessId}`)
+  if (api.resumeThread(threadHandle) === 0xFFFFFFFF) {
+    // Closing the job triggers kill-on-close, so the suspended child dies
+    // instead of hanging until this process exits; the process/thread handles
+    // must go too.
+    const win32Code = api.getLastError()
+    api.closeHandle(threadHandle)
+    api.closeHandle(processHandle)
+    api.closeHandle(job)
+    throwWin32(api, 'ResumeThread', win32Code, `pid ${info.dwProcessId}`)
+  }
   api.closeHandle(threadHandle)
 
   return { pid: info.dwProcessId, process: processHandle, job }
diff --git a/packages/sandbox/sandbox-windows-acl/src/win32-abi.ts b/packages/sandbox/sandbox-windows-acl/src/win32-abi.ts
index 7696605c4e..942862ceb9 100644
--- a/packages/sandbox/sandbox-windows-acl/src/win32-abi.ts
+++ b/packages/sandbox/sandbox-windows-acl/src/win32-abi.ts
@@ -49,13 +49,26 @@ export const SE_GROUP_LOGON_ID = 0xC0000000
 export const STANDARD_RIGHTS_WRITE = 0x00020000 // == READ_CONTROL
 /** FILE_GENERIC_WRITE: every file-write permission bit plus SYNCHRONIZE. */
 export const FILE_GENERIC_WRITE = 0x00120116
-// What the POC grants: FILE_GENERIC_WRITE minus READ_CONTROL; displays as
-// "Write" in Explorer/icacls (windows-acl-restrict-poc.cpp line 16).
+/** DELETE: remove or rename the object (winnt.h line ~3009). */
+export const DELETE = 0x00010000
+/** FILE_DELETE_CHILD: remove or rename a directory's children (winnt.h line ~5907). */
+export const FILE_DELETE_CHILD = 0x0040
+// The POC granted FILE_GENERIC_WRITE minus READ_CONTROL, which displays as
+// "Write" in Explorer/icacls (windows-acl-restrict-poc.cpp line 16). The
+// sandbox grant adds DELETE and FILE_DELETE_CHILD so confined
+// delete/rename/git operations inside the granted trees pass the token's
+// access check too; Write+DELETE displays as "Modify" in icacls.
+// WRITE_DAC/WRITE_OWNER stay OUT deliberately — granting them would let the
+// child take ownership or rewrite DACLs and escape the allowlist (the
+// security boundary).
 /**
- * GRANT_MASK: FILE_GENERIC_WRITE minus READ_CONTROL — the write-access mask
- * the orphan-SID ACEs grant (displays as "Write" in Explorer/icacls).
+ * GRANT_MASK: FILE_GENERIC_WRITE minus READ_CONTROL plus DELETE and
+ * FILE_DELETE_CHILD — the write+delete access mask the orphan-SID ACEs grant
+ * (displays as "Modify" in Explorer/icacls). WRITE_DAC/WRITE_OWNER are
+ * deliberately excluded: they would let the confined child take ownership or
+ * rewrite DACLs.
  */
-export const GRANT_MASK = FILE_GENERIC_WRITE & ~STANDARD_RIGHTS_WRITE // 0x00100116
+export const GRANT_MASK = (FILE_GENERIC_WRITE | DELETE | FILE_DELETE_CHILD) & ~STANDARD_RIGHTS_WRITE // 0x00110156
 
 // CreateRestrictedToken flags (winnt.h lines ~4284)
 /** DISABLE_MAX_PRIVILEGE: strip the token's maximum-privilege elevation so the confined child cannot escalate. */
@@ -68,7 +81,13 @@ export const WRITE_RESTRICTED = 0x8
 // WELL_KNOWN_SID_TYPE (winnt.h lines ~3369-3407)
 /** WinWorldSid: S-1-1-0 (Everyone). */
 export const WinWorldSid = 1
-/** WinLocalSid: S-1-2-0 (LOCAL); CreateWellKnownSid(WinLocalSid) fails with ERROR_INVALID_PARAMETER on Windows 11 build 26200. */
+/**
+ * WinLocalSid: S-1-2-0 (LOCAL) — safe, created successfully on every init
+ * (it sits in every restricted token's restricting list). The
+ * CreateWellKnownSid ERROR_INVALID_PARAMETER failure documented in this
+ * module's header comment belongs to WinLocalLogonSid (S-1-2-1), NOT to
+ * this type.
+ */
 export const WinLocalSid = 2
 /** WinInteractiveSid: S-1-5-4 (INTERACTIVE). */
 export const WinInteractiveSid = 11
@@ -155,6 +174,39 @@ export const ERROR_INSUFFICIENT_BUFFER = 122
 export const ERROR_BROKEN_PIPE = 109
 /** ERROR_NO_DATA: the pipe is being closed. */
 export const ERROR_NO_DATA = 232
+/** ERROR_LOCK_VIOLATION: a byte-range lock conflicts with an existing lock (winerror.h line ~78). */
+export const ERROR_LOCK_VIOLATION = 33
+
+// ---- lock files (fileapi.h / minwinbase.h / winnt.h) -----------------------
+
+// CreateFileW dwDesiredAccess for the ACL lock files: plain read+write is
+// enough to take byte-range locks.
+/** GENERIC_READ: generic read access (winnt.h line ~3028). */
+export const GENERIC_READ = 0x80000000
+/** GENERIC_WRITE: generic write access (winnt.h line ~3029). */
+export const GENERIC_WRITE = 0x40000000
+// CreateFileW dwShareMode: the lock file is shared for read/write but NOT
+// for delete — if a locked file could be deleted and recreated underneath the
+// lock holder, two processes could hold "the same" lock on different files.
+/** FILE_SHARE_READ: other opens may read (winnt.h line ~5949). */
+export const FILE_SHARE_READ = 0x00000001
+/** FILE_SHARE_WRITE: other opens may write (winnt.h line ~5950). */
+export const FILE_SHARE_WRITE = 0x00000002
+/** FILE_SHARE_DELETE: other opens may delete (winnt.h line ~5951) — deliberately NOT used for lock files. */
+export const FILE_SHARE_DELETE = 0x00000004
+/** OPEN_ALWAYS: create the lock file if absent, open it otherwise (fileapi.h line ~21). */
+export const OPEN_ALWAYS = 4
+// LockFileEx dwFlags (minwinbase.h lines ~180-181, included by winbase.h).
+/** LOCKFILE_EXCLUSIVE_LOCK: request an exclusive byte-range lock. */
+export const LOCKFILE_EXCLUSIVE_LOCK = 0x2
+/** LOCKFILE_FAIL_IMMEDIATELY: fail with ERROR_LOCK_VIOLATION instead of waiting. */
+export const LOCKFILE_FAIL_IMMEDIATELY = 0x1
+
+// ACE_HEADER.AceFlags (winnt.h lines ~3477-3524): inherited ACEs shown when
+// reading a DACL are marked with this bit and are not part of the explicit
+// DACL edits this module makes.
+/** INHERITED_ACE: the ACE was inherited from the parent object, not stored explicitly. */
+export const INHERITED_ACE = 0x10
 
 // ---- job object (winnt.h lines ~4859-4866, ~5138, ~5190-5199) --------------
 
diff --git a/packages/sandbox/sandbox-windows-acl/tests/acl.spec.ts b/packages/sandbox/sandbox-windows-acl/tests/acl.spec.ts
new file mode 100644
index 0000000000..fe0bc13acc
--- /dev/null
+++ b/packages/sandbox/sandbox-windows-acl/tests/acl.spec.ts
@@ -0,0 +1,234 @@
+/**
+ * ACL edit tests: the read-merge-write grant keeps pre-existing explicit
+ * ACEs, interleaved sandbox instances do not clobber each other, the
+ * per-path lock primitive is deterministic, and the grant mask carries
+ * DELETE + FILE_DELETE_CHILD (never WRITE_DAC/WRITE_OWNER).
+ *
+ * All state lives in %TEMP% mkdtemp scratch directories; the only exception
+ * is the mandated lock infrastructure under <GetTempPathW()>\dsh-acl-locks,
+ * whose per-test lock file is removed in cleanup.
+ */
+
+import { mkdtempSync, rmSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { afterEach, describe, expect, it } from 'vitest'
+import koffi from 'koffi'
+
+import { buildExplicitAccess, grantWrite, lockFilePath, revokeWrite, withPathLock } from '../src/acl.ts'
+import { AclSandbox } from '../src/index.ts'
+import { allocOverlapped, allocPtrSlot, decodePtr, isInvalidHandle, isNullPtr, win32 } from '../src/ffi.ts'
+import type { NativePtr, Win32Bindings } from '../src/ffi.ts'
+import * as abi from '../src/win32-abi.ts'
+
+const isWin32 = process.platform === 'win32'
+
+/** FILE_READ_DATA (winnt.h line ~5895): the harmless mask the explicit test ACE grants. */
+const FILE_READ_DATA = 0x0001
+
+/** koffi SID layout: revision@0, subAuthorityCount@1, identifierAuthority@2 (6 bytes, big-endian), subAuthority@8. */
+const SID_STRUCT = koffi.struct('DSH_ACL_SPEC_SID', {
+  revision: 'uint8',
+  subAuthorityCount: 'uint8',
+  identifierAuthority: 'uint8[6]',
+  subAuthority: 'uint32[8]',
+})
+
+interface SidLayout {
+  revision: number
+  subAuthorityCount: number
+  identifierAuthority: number[]
+  subAuthority: number[]
+}
+
+/** One direct (explicit, non-inherited) allow ACE of a directory DACL. */
+interface DirectAce {
+  sid: string
+  mask: number
+}
+
+/** Convert one SID string to a LocalAlloc'd SID pointer (caller frees). */
+function sidFromString(api: Win32Bindings, sid: string): NativePtr {
+  const slot = allocPtrSlot()
+  if (api.convertStringSidToSidW(sid, slot) === 0) throw new Error(`ConvertStringSidToSidW failed for ${sid}`)
+  const ptr = decodePtr(slot)
+  if (ptr === null) throw new Error(`ConvertStringSidToSidW returned null for ${sid}`)
+  return ptr
+}
+
+/** Stringify a decoded SID layout (identifierAuthority bytes 2..5 are the big-endian value). */
+function sidString(sid: SidLayout): string {
+  const authority = ((sid.identifierAuthority[2] ?? 0) << 24)
+    | ((sid.identifierAuthority[3] ?? 0) << 16)
+    | ((sid.identifierAuthority[4] ?? 0) << 8)
+    | (sid.identifierAuthority[5] ?? 0)
+  const subs = sid.subAuthority.slice(0, sid.subAuthorityCount).join('-')
+  return `S-${sid.revision}-${authority}${sid.subAuthorityCount > 0 ? `-${subs}` : ''}`
+}
+
+/**
+ * Read the directory's explicit allow ACEs (inherited ACEs excluded): each
+ * ACE header is AceType@0, AceFlags@1, AceSize@2 (winnt.h lines ~3477-3480);
+ * ACCESS_ALLOWED_ACE stores Mask@4 and the inline SID@8. The ACL pointer sits
+ * inside the descriptor allocation — only the descriptor is LocalFree'd.
+ */
+function readDirectAces(api: Win32Bindings, path: string): DirectAce[] {
+  const ownerSlot = allocPtrSlot()
+  const groupSlot = allocPtrSlot()
+  const daclSlot = allocPtrSlot()
+  const saclSlot = allocPtrSlot()
+  const descriptorSlot = allocPtrSlot()
+  const readResult = api.getNamedSecurityInfoW(
+    path, abi.SE_FILE_OBJECT, abi.DACL_SECURITY_INFORMATION,
+    ownerSlot, groupSlot, daclSlot, saclSlot, descriptorSlot,
+  )
+  if (readResult !== abi.ERROR_SUCCESS) throw new Error(`GetNamedSecurityInfoW failed (${readResult}) for ${path}`)
+  const acl = decodePtr(daclSlot)
+  const descriptor = decodePtr(descriptorSlot)
+  try {
+    if (acl === null) return []
+    const aclSize = koffi.decode(acl, 2, 'uint16') as number
+    const aces: DirectAce[] = []
+    for (let offset = 8; offset + 8 <= aclSize;) {
+      const flags = koffi.decode(acl, offset + 1, 'uint8') as number
+      const aceSize = koffi.decode(acl, offset + 2, 'uint16') as number
+      if ((flags & abi.INHERITED_ACE) === 0) {
+        aces.push({ sid: sidString(koffi.decode(acl, offset + 8, SID_STRUCT) as SidLayout), mask: koffi.decode(acl, offset + 4, 'uint32') as number })
+      }
+      offset += aceSize
+    }
+    return aces
+  } finally {
+    if (descriptor !== null) api.localFree(descriptor)
+  }
+}
+
+describe.skipIf(!isWin32)('ACL editing', () => {
+  const scratchDirs: string[] = []
+  afterEach(() => {
+    for (const dir of scratchDirs.splice(0)) rmSync(dir, { recursive: true, force: true })
+  })
+
+  function scratch(): string {
+    const dir = mkdtempSync(join(tmpdir(), 'dsh-acl-edit-'))
+    scratchDirs.push(dir)
+    return dir
+  }
+
+  it('grantWrite merges into the current DACL: an explicit Users ACE survives grant+revoke', async () => {
+    const api = await win32()
+    const dir = scratch()
+    const usersSid = sidFromString(api, 'S-1-5-32-545')
+    const orphanSid = sidFromString(api, 'S-1-4-4242-1')
+    try {
+      // Install one explicit ACE (Users + benign read mask) with the
+      // package's own bindings, exactly like a pre-existing explicit DACL
+      // entry another sandbox instance or administrator added.
+      const newAclSlot = allocPtrSlot()
+      const mergeResult = api.setEntriesInAclW(1, buildExplicitAccess(usersSid, abi.GRANT_ACCESS, FILE_READ_DATA), null, newAclSlot)
+      expect(mergeResult, `SetEntriesInAclW setup (${mergeResult})`).toBe(abi.ERROR_SUCCESS)
+      const newAcl = decodePtr(newAclSlot)
+      expect(newAcl).not.toBeNull()
+      const applyResult = api.setNamedSecurityInfoW(
+        dir, abi.SE_FILE_OBJECT, abi.DACL_SECURITY_INFORMATION, null, null, newAcl, null,
+      )
+      const freed = newAcl === null ? null : api.localFree(newAcl)
+      expect(applyResult, `SetNamedSecurityInfoW setup (${applyResult})`).toBe(abi.ERROR_SUCCESS)
+      expect(isNullPtr(freed)).toBe(true)
+
+      grantWrite(api, dir, orphanSid)
+      revokeWrite(api, dir, orphanSid)
+
+      const aces = readDirectAces(api, dir)
+      expect(aces.some(ace => ace.sid === 'S-1-5-32-545')).toBe(true) // explicit ACE preserved
+      expect(aces.some(ace => ace.sid === 'S-1-4-4242-1')).toBe(false) // orphan grant fully removed
+    } finally {
+      if (!isNullPtr(usersSid)) api.localFree(usersSid)
+      if (!isNullPtr(orphanSid)) api.localFree(orphanSid)
+    }
+  })
+
+  it('interleaved sandbox instances: A.init → B.init → A.dispose → B.dispose leaves neither ACE', async () => {
+    const api = await win32()
+    const dir = scratch()
+    const sandboxA = new AclSandbox({ writableDirs: [dir], tempDir: null, writeSid: 'S-1-4-9000-1' })
+    const sandboxB = new AclSandbox({ writableDirs: [dir], tempDir: null, writeSid: 'S-1-4-9000-2' })
+    await sandboxA.init()
+    await sandboxB.init()
+    sandboxA.dispose()
+    sandboxB.dispose()
+    const aces = readDirectAces(api, dir)
+    expect(aces.some(ace => ace.sid === 'S-1-4-9000-1')).toBe(false)
+    expect(aces.some(ace => ace.sid === 'S-1-4-9000-2')).toBe(false)
+  })
+
+  it('the per-path lock is exclusive: a second immediate lock attempt fails with ERROR_LOCK_VIOLATION until release', async () => {
+    const api = await win32()
+    const dir = scratch()
+    const lockPath = lockFilePath(api, dir)
+    const open = (): NativePtr => api.createFileW(
+      lockPath, abi.GENERIC_READ | abi.GENERIC_WRITE,
+      abi.FILE_SHARE_READ | abi.FILE_SHARE_WRITE, null, abi.OPEN_ALWAYS, 0, null,
+    )
+    const first = open()
+    const second = open()
+    expect(isInvalidHandle(first)).toBe(false)
+    expect(isInvalidHandle(second)).toBe(false)
+    try {
+      expect(api.lockFileEx(first, abi.LOCKFILE_EXCLUSIVE_LOCK, 0, 1, 0, allocOverlapped())).toBe(1)
+      expect(api.lockFileEx(second, abi.LOCKFILE_EXCLUSIVE_LOCK | abi.LOCKFILE_FAIL_IMMEDIATELY, 0, 1, 0, allocOverlapped())).toBe(0)
+      expect(api.getLastError()).toBe(abi.ERROR_LOCK_VIOLATION)
+      expect(api.unlockFileEx(first, 0, 1, 0, allocOverlapped())).toBe(1)
+      expect(api.lockFileEx(second, abi.LOCKFILE_EXCLUSIVE_LOCK | abi.LOCKFILE_FAIL_IMMEDIATELY, 0, 1, 0, allocOverlapped())).toBe(1)
+      expect(api.unlockFileEx(second, 0, 1, 0, allocOverlapped())).toBe(1)
+    } finally {
+      api.closeHandle(first)
+      api.closeHandle(second)
+      rmSync(lockPath, { force: true })
+    }
+  })
+
+  it('withPathLock serializes the action and releases the lock even when the action throws', async () => {
+    const api = await win32()
+    const dir = scratch()
+    const lockPath = lockFilePath(api, dir)
+    let attempts = 0
+    expect(() => withPathLock(api, dir, () => {
+      attempts++
+      throw new Error('action failure')
+    })).toThrow('action failure')
+    expect(attempts).toBe(1)
+    // The lock was released: a fresh immediate lock succeeds.
+    const handle = api.createFileW(
+      lockPath, abi.GENERIC_READ | abi.GENERIC_WRITE,
+      abi.FILE_SHARE_READ | abi.FILE_SHARE_WRITE, null, abi.OPEN_ALWAYS, 0, null,
+    )
+    expect(isInvalidHandle(handle)).toBe(false)
+    try {
+      expect(api.lockFileEx(handle, abi.LOCKFILE_EXCLUSIVE_LOCK | abi.LOCKFILE_FAIL_IMMEDIATELY, 0, 1, 0, allocOverlapped())).toBe(1)
+      expect(api.unlockFileEx(handle, 0, 1, 0, allocOverlapped())).toBe(1)
+    } finally {
+      api.closeHandle(handle)
+      rmSync(lockPath, { force: true })
+    }
+  })
+
+  it('the applied grant mask carries DELETE and FILE_DELETE_CHILD (never WRITE_DAC/WRITE_OWNER)', async () => {
+    const api = await win32()
+    const dir = scratch()
+    const sandbox = new AclSandbox({ writableDirs: [dir], tempDir: null, writeSid: 'S-1-4-1234-5' })
+    try {
+      await sandbox.init()
+      const grant = readDirectAces(api, dir).find(ace => ace.sid === 'S-1-4-1234-5')
+      expect(grant).toBeDefined()
+      const mask = grant?.mask ?? 0
+      expect(mask).toBe(abi.GRANT_MASK)
+      expect(mask & abi.DELETE).toBe(abi.DELETE)
+      expect(mask & abi.FILE_DELETE_CHILD).toBe(abi.FILE_DELETE_CHILD)
+      expect(mask & 0x00040000).toBe(0) // WRITE_DAC must never be granted
+      expect(mask & 0x00080000).toBe(0) // WRITE_OWNER must never be granted
+    } finally {
+      sandbox.dispose()
+    }
+  })
+})
diff --git a/packages/sandbox/sandbox-windows-acl/tests/failure-paths.spec.ts b/packages/sandbox/sandbox-windows-acl/tests/failure-paths.spec.ts
new file mode 100644
index 0000000000..14f370602c
--- /dev/null
+++ b/packages/sandbox/sandbox-windows-acl/tests/failure-paths.spec.ts
@@ -0,0 +1,112 @@
+/**
+ * Failure-path unit tests with minimal stub binding tables: the spawn
+ * helpers must close every handle they created before throwing, and
+ * getTempPath must refuse to decode a buffer GetTempPathW never wrote.
+ * Pure stubs — no real Win32 calls, so these run on every platform.
+ */
+
+import { describe, expect, it, vi } from 'vitest'
+import koffi from 'koffi'
+
+import { PROCESS_INFORMATION, getTempPath } from '../src/ffi.ts'
+import type { NativePtr, Win32Bindings } from '../src/ffi.ts'
+import { Win32Error } from '../src/errors.ts'
+import { spawnSandboxed, spawnSandboxedInherited } from '../src/spawn.ts'
+
+const PVOID = koffi.pointer('void')
+
+/** The stub the CreateProcessAsUserW failure branch needs: pipes "succeed", the spawn fails with Win32 5. */
+function pipeFailureApi(): { api: Win32Bindings; closed: bigint[]; closeHandle: ReturnType<typeof vi.fn> } {
+  const closed: bigint[] = []
+  let next = 1n
+  const closeHandle = vi.fn((handle: NativePtr) => {
+    closed.push(handle)
+    return 1
+  })
+  const api = {
+    createPipe: vi.fn((readSlot: NativePtr, writeSlot: NativePtr) => {
+      koffi.encode(readSlot, PVOID, next++)
+      koffi.encode(writeSlot, PVOID, next++)
+      return 1
+    }),
+    setHandleInformation: vi.fn(() => 1),
+    createProcessAsUserW: vi.fn(() => 0),
+    getLastError: vi.fn(() => 5), // ERROR_ACCESS_DENIED: the failure the branch reports
+    closeHandle,
+    formatMessageW: vi.fn(() => 0),
+  } as unknown as Win32Bindings
+  return { api, closed, closeHandle }
+}
+
+/** The stub the ResumeThread failure branch needs: everything succeeds until ResumeThread returns 0xFFFFFFFF. */
+function resumeFailureApi(): { api: Win32Bindings; closed: bigint[]; closeHandle: ReturnType<typeof vi.fn> } {
+  const closed: bigint[] = []
+  let std = 50n
+  const closeHandle = vi.fn((handle: NativePtr) => {
+    closed.push(handle)
+    return 1
+  })
+  const api = {
+    createJobObjectW: vi.fn(() => 100n),
+    setInformationJobObject: vi.fn(() => 1),
+    getStdHandle: vi.fn(() => std++),
+    setHandleInformation: vi.fn(() => 1),
+    createProcessAsUserW: vi.fn((
+      _token: unknown, _app: unknown, _cmd: unknown, _pa: unknown, _ta: unknown,
+      _inherit: unknown, _flags: unknown, _env: unknown, _cwd: unknown, _si: unknown, processInfo: NativePtr,
+    ) => {
+      koffi.encode(processInfo, PROCESS_INFORMATION, { hProcess: 200n, hThread: 201n, dwProcessId: 1234, dwThreadId: 5678 })
+      return 1
+    }),
+    assignProcessToJobObject: vi.fn(() => 1),
+    resumeThread: vi.fn(() => 0xFFFFFFFF),
+    getLastError: vi.fn(() => 5),
+    closeHandle,
+    formatMessageW: vi.fn(() => 0),
+  } as unknown as Win32Bindings
+  return { api, closed, closeHandle }
+}
+
+describe('spawn failure paths close their handles', () => {
+  // A dummy token value; the stubbed spawn never reads it.
+  const token = 1n as NativePtr
+
+  it('spawnSandboxed closes all six pipe handles before throwing when CreateProcessAsUserW fails', () => {
+    const { api, closed, closeHandle } = pipeFailureApi()
+    let caught: unknown
+    try {
+      spawnSandboxed(api, token, { command: 'probe.exe', args: [], cwd: 'C:\\' })
+    } catch (error) {
+      caught = error
+    }
+    expect(caught).toBeInstanceOf(Win32Error)
+    expect((caught as Win32Error).api).toBe('CreateProcessAsUserW')
+    expect((caught as Win32Error).win32Code).toBe(5)
+    expect(closeHandle).toHaveBeenCalledTimes(6)
+    expect(closed).toEqual([1n, 2n, 3n, 4n, 5n, 6n])
+  })
+
+  it('spawnSandboxedInherited closes thread, process, and kill-on-close job before throwing when ResumeThread fails', () => {
+    const { api, closed, closeHandle } = resumeFailureApi()
+    let caught: unknown
+    try {
+      spawnSandboxedInherited(api, token, { command: 'probe.exe', args: [], cwd: 'C:\\' })
+    } catch (error) {
+      caught = error
+    }
+    expect(caught).toBeInstanceOf(Win32Error)
+    expect((caught as Win32Error).api).toBe('ResumeThread')
+    expect((caught as Win32Error).win32Code).toBe(5)
+    // thread, process, job — closing the job triggers kill-on-close so the
+    // suspended child dies instead of hanging until this process exits.
+    expect(closeHandle).toHaveBeenCalledTimes(3)
+    expect(closed).toEqual([201n, 200n, 100n])
+  })
+})
+
+describe('getTempPath buffer defense', () => {
+  it('throws a clear error instead of decoding a buffer GetTempPathW never wrote', () => {
+    const api = { getTempPathW: vi.fn(() => 300) } as unknown as Win32Bindings // 300 > the 261-char buffer
+    expect(() => getTempPath(api)).toThrow(/GetTempPathW failed \(Win32 122\): required 300/u)
+  })
+})
diff --git a/packages/sandbox/sandbox-windows-acl/tests/quote.spec.ts b/packages/sandbox/sandbox-windows-acl/tests/quote.spec.ts
new file mode 100644
index 0000000000..5af00fb9cb
--- /dev/null
+++ b/packages/sandbox/sandbox-windows-acl/tests/quote.spec.ts
@@ -0,0 +1,88 @@
+/**
+ * quoteArg unit tests plus a round-trip through the REAL CommandLineToArgvW
+ * parser (shell32.dll, shellapi.h line ~867:
+ * `LPWSTR *CommandLineToArgvW(LPCWSTR lpCmdLine, int *pNumArgs)`) on win32.
+ *
+ * CommandLineToArgvW applies the documented backslash rule (2n backslashes
+ * before a quote produce n backslashes and toggle quoting; 2n+1 produce n
+ * backslashes and a literal quote) to every token EXCEPT the first — the
+ * first token is parsed with backslashes literal and quotes toggling
+ * (verified empirically on this machine, Windows 11 build 26200). The
+ * round-trip therefore prepends a plain program token, exactly like
+ * buildCommandLine's real callers do, so the arguments under test land on
+ * the rule-applying tokens.
+ *
+ * Reading argv from CommandLineToArgvW: koffi cannot decode the returned
+ * LPWSTR* contents directly (the pointed-to strings are not koffi-registered
+ * references), so each string is copied with lstrcpynW (winbase.h line
+ * ~1500) into a Node Buffer and read as UTF-16LE; lengths come from
+ * lstrlenW (winbase.h line ~1506); the argv block is freed with LocalFree
+ * (winbase.h line ~1127) — CommandLineToArgvW's documented contract.
+ */
+
+import { describe, expect, it } from 'vitest'
+
+import { buildCommandLine, quoteArg } from '../src/spawn.ts'
+
+const isWin32 = process.platform === 'win32'
+
+/**
+ * Table cases: input argv entry → the exact command-line fragment quoteArg
+ * must produce. Trailing-backslash inputs are the regression: the closing
+ * quote must be preceded by DOUBLED backslashes, or the parser reads them as
+ * escaping the closing quote.
+ */
+const cases: Array<[input: string, quoted: string]> = [
+  ['', '""'],
+  ['a', 'a'],
+  ['a b', '"a b"'],
+  ['a"b', '"a\\"b"'],
+  ['a\\b', 'a\\b'],
+  ['a b\\', '"a b\\\\"'],
+  ['a b\\\\', '"a b\\\\\\\\"'],
+  ['a b\\\\\\', '"a b\\\\\\\\\\\\"'],
+  ['a\\\\"b', '"a\\\\\\\\\\"b"'],
+]
+
+describe('quoteArg', () => {
+  it.each(cases)('quotes %j as %j', (input, quoted) => {
+    expect(quoteArg(input)).toBe(quoted)
+  })
+})
+
+describe.skipIf(!isWin32)('CommandLineToArgvW round-trip', () => {
+  it('parses quoteArg+join back to the exact original argv', async () => {
+    const { default: koffi } = await import('koffi')
+    const PVOID = koffi.pointer('void')
+    const shell32 = koffi.load('shell32.dll')
+    const kernel32 = koffi.load('kernel32.dll')
+    const commandLineToArgvW = shell32.func('__stdcall', 'CommandLineToArgvW', PVOID, ['str16', koffi.pointer('int')])
+    const lstrcpynW = kernel32.func('__stdcall', 'lstrcpynW', PVOID, [PVOID, PVOID, 'int'])
+    const lstrlenW = kernel32.func('__stdcall', 'lstrlenW', 'int', [PVOID])
+    const localFree = kernel32.func('__stdcall', 'LocalFree', PVOID, [PVOID])
+
+    const parse = (commandLine: string): string[] => {
+      const countSlot = koffi.alloc('int', 1) as unknown
+      const argvBlock = commandLineToArgvW(commandLine, countSlot) as unknown
+      try {
+        if (argvBlock === null) throw new Error('CommandLineToArgvW returned NULL')
+        const count = koffi.decode(countSlot, 0, 'int') as number
+        const table = Buffer.from(koffi.view(argvBlock, count * 8))
+        const parsed: string[] = []
+        for (let index = 0; index < count; index++) {
+          const stringAddress = table.readBigUInt64LE(index * 8)
+          const copied = Buffer.alloc(2048)
+          lstrcpynW(copied, stringAddress, copied.length / 2)
+          const length = lstrlenW(copied) as number
+          parsed.push(copied.subarray(0, length * 2).toString('utf16le'))
+        }
+        return parsed
+      } finally {
+        localFree(argvBlock)
+      }
+    }
+
+    const argv = ['', 'a', 'a b', 'a"b', 'a\\b', 'a b\\', 'a b\\\\', 'a b\\\\\\', 'a\\\\"b']
+    expect(parse(buildCommandLine('prog.exe', argv))).toEqual(['prog.exe', ...argv])
+  })
+})
diff --git a/packages/sandbox/sandbox-windows-acl/tests/runner.spec.ts b/packages/sandbox/sandbox-windows-acl/tests/runner.spec.ts
index f188423425..680d65b253 100644
--- a/packages/sandbox/sandbox-windows-acl/tests/runner.spec.ts
+++ b/packages/sandbox/sandbox-windows-acl/tests/runner.spec.ts
@@ -12,16 +12,16 @@ import { join } from 'node:path'
 import { fileURLToPath } from 'node:url'
 import { afterAll, beforeAll, describe, expect, it } from 'vitest'
 
+import { resolvePwshPath } from '@deepseek-ai/dsh-pwsh-local'
+
 const isWin32 = process.platform === 'win32'
 const runnerEntry = fileURLToPath(new URL('../src/runner.ts', import.meta.url))
 
+// Functional probe, not where.exe: spawnSync never throws on a missing
+// binary (status null) and where.exe exits 1 without pwsh — only an actual
+// pwsh invocation's exit status is truth.
 function pwshAvailable(): boolean {
-  try {
-    spawnSync('where.exe', ['pwsh'], { stdio: 'ignore' })
-    return true
-  } catch {
-    return false
-  }
+  return spawnSync(resolvePwshPath(), ['-NoLogo', '-NoProfile', '-NonInteractive', '-Command', '$true'], { encoding: 'utf8' }).status === 0
 }
 
 function runRunner(args: string[], timeoutMs = 30_000) {
@@ -99,6 +99,31 @@ describe.skipIf(!isWin32 || !pwshAvailable())('windows-acl runner', () => {
     expect(existsSync(join(writableDir, 'readonly-child-wrote.txt'))).toBe(false)
   }, 30_000)
 
+  it('workspace-write: Remove-Item and Rename-Item succeed in the granted workspace (DELETE + FILE_DELETE_CHILD)', () => {
+    // Deleting a file and renaming a directory both hit the second access
+    // check on the workspace itself: the grant must carry DELETE (on the
+    // object) and FILE_DELETE_CHILD (on its parent).
+    const victimFile = join(writableDir, 'delete-me.txt')
+    writeFileSync(victimFile, 'remove me')
+    const victimDir = join(writableDir, 'rename-me')
+    mkdirSync(victimDir)
+    const renamedDir = join(writableDir, 'renamed-by-child')
+    const probe = [
+      "$ErrorActionPreference='SilentlyContinue';",
+      `try{Remove-Item -LiteralPath '${victimFile}' -ErrorAction Stop;'DELETE-FILE: OK'}catch{'DELETE-FILE: DENIED'};`,
+      `try{Rename-Item -LiteralPath '${victimDir}' -NewName 'renamed-by-child' -ErrorAction Stop;'RENAME-DIR: OK'}catch{'RENAME-DIR: DENIED'}`,
+    ].join('')
+    const result = runRunner([
+      '--workspace', writableDir, '--temp', isolatedTemp, '--mode', 'workspace-write',
+      '--', 'pwsh', '/NoLogo', '/NonInteractive', '/NoProfile', '/Command', probe,
+    ])
+    expect(result.status, `stderr: ${result.stderr}`).toBe(0)
+    expect(result.stdout).toContain('DELETE-FILE: OK')
+    expect(result.stdout).toContain('RENAME-DIR: OK')
+    expect(existsSync(victimFile)).toBe(false)
+    expect(existsSync(renamedDir)).toBe(true)
+  }, 30_000)
+
   it('runner-side failure: signature on stderr and exit 127, the command never runs', () => {
     const result = runRunner(['--workspace', writableDir, '--temp', isolatedTemp, '--mode', 'workspace-write'])
     expect(result.status).toBe(127)
diff --git a/packages/sandbox/sandbox-windows-acl/verify/abi-probe.cpp b/packages/sandbox/sandbox-windows-acl/verify/abi-probe.cpp
index 914326acdc..866fda7160 100644
--- a/packages/sandbox/sandbox-windows-acl/verify/abi-probe.cpp
+++ b/packages/sandbox/sandbox-windows-acl/verify/abi-probe.cpp
@@ -88,6 +88,20 @@ int wmain()
 	P(FILE_GENERIC_WRITE);
 	P((FILE_GENERIC_WRITE & ~STANDARD_RIGHTS_WRITE));
 	P(STANDARD_RIGHTS_WRITE);
+	P(DELETE);
+	P(FILE_DELETE_CHILD);
+	P(((FILE_GENERIC_WRITE | DELETE | FILE_DELETE_CHILD) & ~STANDARD_RIGHTS_WRITE));
+
+	P(FILE_SHARE_READ);
+	P(FILE_SHARE_WRITE);
+	P(FILE_SHARE_DELETE);
+	P(GENERIC_READ);
+	P(GENERIC_WRITE);
+	P(OPEN_ALWAYS);
+	P(LOCKFILE_EXCLUSIVE_LOCK);
+	P(LOCKFILE_FAIL_IMMEDIATELY);
+	P(ERROR_LOCK_VIOLATION);
+	P(INHERITED_ACE);
 
 	P(DISABLE_MAX_PRIVILEGE);
 	P(SANDBOX_INERT);
@@ -163,7 +177,14 @@ int wmain()
 	static_assert(TOKEN_QUERY == 0x8 && TOKEN_DUPLICATE == 0x2 && TOKEN_ADJUST_DEFAULT == 0x80 && TOKEN_ASSIGN_PRIMARY == 0x1, "token rights");
 	static_assert(SE_GROUP_LOGON_ID == 0xC0000000, "logon id attr");
 	static_assert(FILE_GENERIC_WRITE == 0x120116, "generic write");
-	static_assert((FILE_GENERIC_WRITE & ~STANDARD_RIGHTS_WRITE) == 0x100116, "grant mask");
+	static_assert((FILE_GENERIC_WRITE & ~STANDARD_RIGHTS_WRITE) == 0x100116, "poc grant mask");
+	static_assert(DELETE == 0x10000 && FILE_DELETE_CHILD == 0x40, "delete rights");
+	static_assert(((FILE_GENERIC_WRITE | DELETE | FILE_DELETE_CHILD) & ~STANDARD_RIGHTS_WRITE) == 0x110156, "sandbox grant mask");
+	static_assert(FILE_SHARE_READ == 0x1 && FILE_SHARE_WRITE == 0x2 && FILE_SHARE_DELETE == 0x4, "share modes");
+	static_assert(OPEN_ALWAYS == 4, "open always");
+	static_assert(LOCKFILE_EXCLUSIVE_LOCK == 0x2 && LOCKFILE_FAIL_IMMEDIATELY == 0x1, "lockfile flags");
+	static_assert(ERROR_LOCK_VIOLATION == 33, "lock violation");
+	static_assert(INHERITED_ACE == 0x10, "inherited ace flag");
 	static_assert(GRANT_ACCESS == 1 && REVOKE_ACCESS == 4, "access modes");
 	static_assert(SUB_CONTAINERS_AND_OBJECTS_INHERIT == 0x3, "inheritance");
 	static_assert(CREATE_NO_WINDOW == 0x08000000, "create no window");
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index b06386f144..d08966c17a 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -4654,6 +4654,9 @@ importers:
       '@deepseek-ai/dsh-invariants':
         specifier: workspace:^
         version: link:../../support/invariants
+      '@deepseek-ai/dsh-pwsh-local':
+        specifier: workspace:^
+        version: link:../../bash/pwsh-local
       '@deepseek-ai/dsh-sandbox-local':
         specifier: workspace:^
         version: link:../sandbox-local