Bash tool stdout pipe broken on Windows - commands execute but output not captured (v2.1.45)

Description

On Windows 11 (Git Bash), the Bash tool's stdout/stderr capture pipe is broken. Commands execute correctly internally but Claude Code receives no output and falsely reports exit code 1.

Environment

• Claude Code version: 2.1.45
• OS: Windows 11 Pro 10.0.26100
• Shell: Git Bash (git version 2.44.0.windows.1)
• Bash path: /usr/bin/bash (MSYS2/MinGW64)

Reproduction

Every Bash tool call returns exit code 1 with zero stdout/stderr:

Bash("echo hello")     → Exit code 1, no output
Bash("pwd")            → Exit code 1, no output
Bash("whoami")         → Exit code 1, no output

Proof that commands execute correctly

Redirecting output to a temp file and reading it back confirms the shell works:

Bash("echo 'bash is alive' > /tmp/test.txt 2>&1 || true")  → exit 0
Read("/tmp/test.txt")  → "bash is alive"

Bash("echo \$? > /tmp/exit.txt || true")  → exit 0
Read("/tmp/exit.txt")  → "0"   (commands actually succeed)

Bash("git status --porcelain > /tmp/gs.txt 2>&1 || true")  → exit 0
Read("/tmp/gs.txt")    → correct git status output

Key findings

1. Shell subprocess IS running — commands execute, files are written, git works
2. stdout/stderr pipe to Claude Code is broken — output never reaches the tool result handler
3. Exit code 1 is artificial — actual command exit codes are 0
4. || true forces exit 0 but output still not captured
5. Persists across session restarts — not a one-time session corruption
6. Not a permissions issue — fails with dangerouslyDisableSandbox: true
7. No shell profile interference — no .bashrc/.bash_profile, /etc/profile is stock MSYS2
8. Sandbox is not the cause — same behavior with sandbox disabled

Workaround

Redirect output to temp file and read it back:

Bash("command > /tmp/out.txt 2>&1 || true")
Read("/tmp/out.txt")

Impact

All Bash tool functionality is effectively broken — git operations, build commands, process management, etc. all appear to fail despite actually succeeding. The Read/Write/Edit/Grep/Glob tools still work, as do MCP tools.