Bash tool: heredoc fails with 'can't create temp file for here document'

Bug description

The Bash tool cannot execute heredocs. Any command using a here document fails with:

(eval):1: can't create temp file for here document: no such file or directory

This is notable because the system prompt explicitly instructs Claude to use heredocs for git commit messages:

ALWAYS pass the commit message via a HEREDOC

Steps to reproduce

Run any heredoc via the Bash tool:

cat <<'EOF'
hello world
EOF

Or the recommended commit pattern from the system prompt:

git commit -m "$(cat <<'EOF'
My commit message
EOF
)"

Both fail with the same error.

Expected behavior

Heredocs should work as in a normal shell session. The $TMPDIR directory exists and is writable:

TMPDIR=/var/folders/97/…/T/
drwx------ nicolas staff …/T/

Actual behavior

The error (eval):1: can't create temp file for here document: no such file or directory is raised. The (eval):1 prefix suggests the Bash tool passes commands through eval, which may interfere with heredoc temp file creation in zsh.

Impact

• Claude falls back to inline -m "message" for commits, which can break with special characters or multi-line messages.
• Any script or command relying on heredocs cannot be executed via the Bash tool.

Environment

• Claude Code: 2.1.81
• Shell: zsh 5.9 (arm64-apple-darwin25.0)
• macOS: 26.4 (build 25E246)
• No sandbox active