Regression in Homebrew Codex CLI 0.144.1: GPT-5.6 Code Mode fails with code-mode host exited during handshake, while ChatGPT bundled CLI works

What version of Codex CLI is running?

0.144.1

What subscription do you have?

plus

Which model were you using?

GPT-5.6 (sol / terra / luna)

What platform is your computer?

Darwin 25.5.0 arm64 arm

What terminal emulator and version are you using (if applicable)?

cmux, iterm2, vscode all

Codex doctor report

What issue are you seeing?

The Homebrew Codex CLI consistently fails to execute Code Mode tool calls with GPT-5.6 models.

Example:

codex exec -m gpt-5.6-terra "pwd"

The tool invocation fails with:

ERROR codex_core::tools::router:

error=code-mode host exited during handshake

The model then answers using the provided environment information instead of actually executing the shell command.

---

What steps can reproduce the bug?

1. Install Codex CLI 0.144.1 via Homebrew.

1. Login with a ChatGPT account.

1. Run:

codex exec -m gpt-5.6-terra "Run pwd using the shell tool."

or start an interactive session:

codex -m gpt-5.6-terra

and ask:

pwd

What is the expected behavior?

Expected behavior

The shell tool should execute successfully.

Example output:

exec

/bin/zsh -lc pwd

Succeeded

/Users/...

---

Actual behavior

The shell tool never executes.

ERROR codex_core::tools::router:

code-mode host exited during handshake

---

Additional information

I spent quite a while isolating this.

The following all work correctly:

• ChatGPT macOS bundled Codex CLI (0.144.0-alpha.4)

• GPT-5.5

• ChatGPT App (same account, same machine)

The following consistently fails:

• Homebrew Codex CLI 0.144.1

• GPT-5.6 Terra Code Mode

• GPT-5.6 Sol Code Mode (tool invocation)

The most convincing reproduction is that the exact same machine, account, repository and prompt work correctly when using the Codex binary bundled inside the ChatGPT macOS app, but fail when using the Homebrew CLI.

Working:

"/Applications/ChatGPT.app/Contents/Resources/codex" exec \

  -m gpt-5.6-terra \

  "Run pwd using the shell tool."

Output:

exec

/bin/zsh -lc pwd

Succeeded

Failing:

codex exec \

  -m gpt-5.6-terra \

  "Run pwd using the shell tool."

Output:

ERROR codex_core::tools::router:

error=code-mode host exited during handshake

---

Diagnostics

codex doctor reports 0 failures.

Environment is healthy:

• Auth OK

• WebSocket OK

• Sandbox OK

• Homebrew install consistent

• No doctor warnings

This looks like a regression specific to the Homebrew 0.144.1 CLI rather than an account or environment issue.