bug: make agent-bootstrap fails on PEP 668 Homebrew Python environments

[Xunzhuo]

Describe the bug

make agent-bootstrap currently calls python3 -m pip install -r tools/agent/requirements.txt directly. On Homebrew-managed Python environments that enforce PEP 668, that fails before any harness tooling is installed.

In the current repository state, the failing command is defined in tools/make/agent.mk line 36.

To Reproduce

1. Use a Homebrew-managed Python environment with PEP 668 enabled.
2. Run:

   make agent-bootstrap

3. Observe the failure:

   error: externally-managed-environment
   

4. As a comparison point, the repo-local .codex-agent-venv can run tools/agent/scripts/agent_gate.py successfully, so the problem is the bootstrap/install path rather than the harness code itself.

Expected behavior

make agent-bootstrap should install agent tooling through a repo-local virtualenv, pipx, or another repo-native path that works on standard Homebrew Python setups without asking contributors to break their system Python configuration.

Affected layer

global level

Additional context

Relevant files:

• tools/make/agent.mk:33-42
• tools/agent/requirements.txt

A small, contributor-friendly fix would be to make agent-bootstrap detect/create a venv and use that interpreter for the install step, while keeping the rest of the harness commands consistent.

[Xunzhuo]

@KJyang-0114 thanks for picking it up. can you comment /assign in your issue before starting it?

[himax12]

/assign #1598