[BUG] teammateMode: "tmux" does not open new tmux panes for Agent Teams in v2.1.74

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?

When teammateMode: "tmux" is set in ~/.claude/settings.json, no new tmux panes are created when Agent Teams are dispatched. Debug logs show [TeammateModeSnapshot] Captured from config: auto even though the
setting is explicitly "tmux" — the setting appears to be ignored at teammate launch time. Agent Teams work but run inline instead of in separate panes.

What Should Happen?

Each teammate agent should open in a new tmux pane/window when teammateMode: "tmux" is configured and Claude is launched from within an active tmux session.

Error Messages/Logs

Steps to Reproduce

1. Set the following in ~/.claude/settings.json:

{
"env": { "CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS": "1" },
"teammateMode": "tmux"
}

1. Start Claude from within a tmux session ($TMUX must be set)
2. Trigger an agent team dispatch via TeamCreate + SendMessage
3. Observe: no new tmux panes are created

Environment: Claude Code 2.1.74 · macOS Darwin 25.3.0 · tmux 3.6a · zsh

Additional context: teammateMode is not supported in project-level settings (schema validation rejects it), so it can only be set globally — which limits per-project configuration.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.74

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

IntelliJ IDEA terminal

Additional Information

Using IntelliJ Terminal with oh-my-zsh