[BUG] Claude Code bash tool fails on HPC/SLURM compute nodes

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?

Claude Code's bash tool fails with EACCES: permission denied, mkdir '/run/user/<UID>' on SLURM compute nodes, even when XDG_RUNTIME_DIR is correctly set to a writable location.
Environment:

Claude Code v2.1.19
SLURM HPC cluster (compute nodes don't have systemd user sessions)
Linux

Notes:

File operations (read/write/search) work fine - only bash tool is affected
Works correctly on login nodes where /run/user/<UID> exists
Node.js/Claude Code appears to hard-code /run/user/<UID> and ignore the environment variable

What Should Happen?

Expected: Bash command executes using the writable XDG_RUNTIME_DIR
Actual: Error: EACCES: permission denied, mkdir '/run/user/5540'

Error Messages/Logs

Error: EACCES: permission denied, mkdir '/run/user/5540'

Steps to Reproduce

SSH to an HPC login node (works fine there)
Get an interactive session on a compute node: srun --pty bash -l
Set XDG_RUNTIME_DIR to a writable path: export XDG_RUNTIME_DIR=/tmp/runtime-$USER-$$; mkdir -p $XDG_RUNTIME_DIR
Verify it's set: echo $XDG_RUNTIME_DIR shows /tmp/runtime-poeschla-2140667
Launch Claude: XDG_RUNTIME_DIR=/tmp/runtime-$USER claude
Try any bash command (e.g., pwd)

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.19 (Claude Code)

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

iTerm2

Additional Information

_No response_