[BUG] Agent spawning steals tmux focus from the user's pane

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?

(This intersects with #23615 but is distinct)

When Claude Code spawns Agent Teams teammates, it creates new tmux panes that steal focus from the user's active pane — the cursor jumps to the new agent pane every time a teammate is spawned.

Impact: When spawning multiple agents in quick succession (common for parallel workloads), the user's pane loses focus repeatedly. Particularly disruptive for daemon-style Claude sessions that spawn agents autonomously — the human loses their cursor mid-typing and can break the command being tmux send-keys pasted

Workaround: None found. Tested tmux set-hook after-split-window "select-pane -l" — focus still jumps (hook may fire before Claude Code's focus switch completes, or Claude Code may use a different mechanism than split-window).

Suggested fix: Add the -d flag to pane creation calls so new panes are created without stealing focus. If Claude Code uses send-keys or another mechanism to switch focus after creation, that should also be gated.

What Should Happen?

Expected: New pane is created in the background. User's focus stays on their active pane.

Error Messages/Logs

Steps to Reproduce

1. Be working in a tmux session with Claude Code
2. Spawn an Agent Teams teammate (via the Agent tool)
3. Focus jumps to the new pane

Claude Model

Not sure / Multiple models

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.1.110

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

iTerm2

Additional Information

_No response_