Support Codex terminal launch

[ShawnPana]

Summary

• Teach the box-agent tmux launcher to seed new terminal windows with Codex when cloud sends launch=codex
• Keep Claude Code launch behavior unchanged, including --dangerously-skip-permissions when enabled
• ACK cloud update_default_agent pushes so the new setting does not show as an unknown command on the agent
• Add a focused unit test for Codex tmux launch command construction

Validation

• python3 -m py_compile agent/box_agent.py agent/test_box_agent.py
• python3 -m unittest agent.test_box_agent

Notes

• Companion cloud PR: https://github.com/browser-use/cloud/pull/4531

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Summary by cubic

Add support for launching Codex in new tmux windows when the cloud sends launch=codex. Claude Code behavior stays the same (including --dangerously-skip-permissions), and the agent now ACKs update_default_agent to avoid noisy warnings.

• New Features

  • Seed first tmux command with Codex and drop to a login shell on exit.
  • Added a focused unit test for Codex tmux command construction.

• Bug Fixes

  • ACK update_default_agent pushes so they don’t appear as unknown commands.

^{Written for commit 6e7b1b6. Summary will update on new commits. Review in cubic}