[BUG] Shell snapshot and cwd temp file errors on every Bash tool call (Windows / MSYS2+Cygwin)

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?

Every Bash tool call produces two spurious errors on stderr, and the entire output (errors + actual command result) is duplicated:

1. Shell snapshot: bash: line 1: /c/Users/<user>/.claude/shell-snapshots/snapshot-bash-<id>.sh: No such file or directory — the file exists on disk with valid content and LF line endings, but bash treats the path as a command to execute rather than a file to source.
2. CWD temp file: bash: line 1: /c/Users/<SHORT~1>/AppData/Local/Temp/claude-<hash>-cwd: No such file or directory — uses Windows 8.3 short name; the file either doesn't exist by the time the command runs, or the short path doesn't resolve.

The exit code is always 1 due to the stderr noise, even when the command itself succeeds.

This produces noisy output that is hard to visually track (did this command actually error out or is it the shell snapshot noise again?), and sometimes Claude gets confused too, saying "hm, that errored. no wait, it didn't. oh, it's the shell noise" which is a waste of time, context and tokens.

What Should Happen?

Bash tool calls should execute cleanly without spurious errors on stderr. The shell snapshot should be sourced (. <path> or source <path>), not executed as a command. The CWD temp file should exist and be accessible when the wrapper script references it. Output should not be duplicated.

Error Messages/Logs

$ echo "hello"
  /usr/bin/bash: line 1:
  /c/Users/MyUserName/.claude/shell-snapshots/snapshot-bash-1771704285950-yledp0.sh: No such file  
  or directory
  hello
  /usr/bin/bash: line 1: /c/Users/MYUSER~1/AppData/Local/Temp/claude-39ac-cwd: No such file or     
  directory

  /usr/bin/bash: line 1:
  /c/Users/MyUserName/.claude/shell-snapshots/snapshot-bash-1771704285950-yledp0.sh: No such file  
  or directory
  hello
  /usr/bin/bash: line 1: /c/Users/MYUSER~1/AppData/Local/Temp/claude-39ac-cwd: No such file or     
  directory


Note: the snapshot file **does** exist — verified with `ls` and `xxd`. It has LF line endings and valid shell content.

Steps to Reproduce

1. Install Claude Code on Windows with MSYS2/Cygwin bash as the default shell
2. Open any project (VS Code extension or CLI)
3. Run any Bash tool call, e.g. echo "hello"
4. Observe: two errors on stderr, duplicated output block, exit code 1

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.50 (Claude Code)

Platform

Other

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

• Windows 10 build 19045
• Shell: GNU bash 5.2.21(1)-release (x86_64-pc-cygwin)
• I run zsh and ohmyzsh as my shell interpreter
• uname: CYGWIN_NT-10.0-19045 3.5.5-1.x86_64
• Claude Code launched via the VS Code extension

P.S.
This report was generated by Claude Code itself after I asked it to dive deeper into what is causing the issue. I'd be happy to do some manual digging too if necessary.