Sandbox cannot create subdirectories under project tmp path

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Title: Sandbox cannot create subdirectories under project tmp path

▎ Body: Bash tool fails with ENOENT: no such file or directory, mkdir when creating subdirectories under
/tmp/claude-1004/-config-projects-13-Al/. Writing files directly to that directory works (via Write tool), but
subdirectory creation fails — breaking Bash, Grep, and Glob tools entirely. Platform: Linux (el9_7), cloud-hosted
Claude Code. Similar to #36759 but the parent dir exists and is writable.

What Should Happen?

Expected behavior: All tools (Bash, Grep, Glob) should work normally. The sandbox should be able to create
subdirectories under its own tmp path, since it can already write files there.

Error Messages/Logs

Steps to Reproduce

1. Open Claude Code (cloud-hosted, claude.ai/code) on a Linux system

▎ 2. Run any Bash command (e.g. git status, echo hello)
▎ 3. The command fails with: ENOENT: no such file or directory, mkdir
'/tmp/claude-1004/-config-projects-13-Al/<UUID>'
▎ 4. Note that the Write tool can successfully write files to /tmp/claude-1004/-config-projects-13-Al/ — only
subdirectory creation fails
▎ 5. The issue persists across sessions/conversations in the same project

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

claude-opus-4-6[1m]

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

_No response_