Bug Report: Bash tool fails to create PTY sessions in iTerm2 (macOS)

[suola]

Describe the bug

Version: GitHub Copilot CLI 1.0.27 (npm install)

OS: macOS, Apple Silicon (arm64)

Terminal: iTerm2 (TERM_PROGRAM=iTerm.app, TERM=xterm-256color)

Shell: zsh 5.9

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Description

The bash tool (used by the agent to run shell commands) completely fails to spawn PTY sessions. Every command attempted immediately returns an invalid shell ID with "no active shell sessions", producing zero output. This makes the agent unable to execute any shell commands.

The ! shell command prefix works fine, meaning process spawning itself is not the issue — only the PTY-based bash tool is broken.

Does NOT reproduce when running Copilot CLI from VS Code (same machine, same user).

Expected Behavior

Shell commands execute normally as they do in VS Code.

Workarounds Attempted (none helped)

• Reinstalled via npm
• Launched with PAGER= unset
• Launched with TERM_PROGRAM= unset
• Relaunched multiple times

Environment

• TERM_PROGRAM=iTerm.app
• TERM=xterm-256color
• SSH_TTY — empty (not SSH)
• ulimit -u (max processes): 2666
• ulimit -n (file descriptors): 10240

Affected version

GitHub Copilot CLI 1.0.27.

Steps to reproduce the behavior

1. Open iTerm2 on macOS
2. Launch copilot in a git repository
3. Ask the agent to run any shell command (e.g. "run git branch")
4. Observe: shell ID is immediately invalid, no output ever produced

Expected behavior

No response

Additional context

-macOS

• iterm2, reproduced with native terminal too