fix(sandbox): reject overlapping Windows temp roots

packages/sandbox/sandbox-windows-acl/src/path-boundary.ts

@@ -0,0 +1,40 @@
+/**
+ * Canonical directory-boundary checks for the Windows ACL workspace and
+ * private-temp capabilities.
+ * @module @deepseek-ai/dsh-sandbox-windows-acl/path-boundary
+ */
+
+import { realpathSync } from 'node:fs'
+import { isAbsolute, relative, sep } from 'node:path'
+
+/** Whether `root` is the same canonical directory as `candidate` or contains it. */
+function containsDirectory(root: string, candidate: string): boolean {
+  const relation = relative(realpathSync.native(root), realpathSync.native(candidate))
+  return relation === '' || (!isAbsolute(relation) && relation !== '..' && !relation.startsWith(`..${sep}`))
+}
+
+/**
+ * Reject a temp parent that is inside the workspace: every child created
+ * below it would inherit the standing workspace capability.
+ * @param workspaceRoot - the canonical workspace root that receives the standing ACE.
+ * @param tempRoot - the existing parent beneath which a private temp child would be created.
+ */
+export function assertTempRootOutsideWorkspace(workspaceRoot: string, tempRoot: string): void {
+  if (containsDirectory(workspaceRoot, tempRoot)) {
+    throw new Error(`Windows ACL temp root must be outside the workspace: workspace=${workspaceRoot}; temp=${tempRoot}`)
+  }
+}
+
+/**
+ * Reject overlap between an actual private temp directory and any writable
+ * directory: either inheritance direction would merge the two capabilities.
+ * @param writableDirs - directories carrying the standing workspace capability.
+ * @param tempDir - the existing directory carrying the revocable temp capability.
+ */
+export function assertPrivateTempDisjoint(writableDirs: readonly string[], tempDir: string): void {
+  for (const writableDir of writableDirs) {
+    if (containsDirectory(writableDir, tempDir) || containsDirectory(tempDir, writableDir)) {
+      throw new Error(`AclSandbox private temp directory must be disjoint from writable directories: writable=${writableDir}; temp=${tempDir}`)
+    }
+  }
+}