fix(browser): isolate Browser Use Python environment

[d31tcjg]

What does this PR do?

Prevents the bundled Browser Use CLI from inheriting Hermes Desktop Python runtime overrides. Desktop can expose Hermes Python 3.11 site-packages through PYTHONPATH while Browser Use runs in an isolated Python 3.12 uv tool environment; the mixed ABI causes ModuleNotFoundError: pydantic_core._pydantic_core before Browser Use can start.

The fix removes PYTHONPATH and PYTHONHOME only at the Browser Use subprocess boundary, after the existing credential-scrubbed browser environment is built. Browser backend credentials, CDP routing, and workspace helper auto-import remain intact.

Related Issue

No existing issue or PR found after searching open and closed work for Browser Use, PYTHONPATH, and pydantic_core.

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 🔒 Security fix
• 📝 Documentation update
• ✅ Tests (adding or improving test coverage)
• ♻️ Refactor (no behavior change)
• 🎯 New skill (bundled or hub)

Changes Made

• Update tools/browser_use_cli.py::_base_subprocess_env() to remove PYTHONPATH and PYTHONHOME before launching Browser Use.
• Add a regression in tests/tools/test_browser_use_cli.py proving both variables are absent, not merely empty, in the child process.

How to Test

1. From a parent process with Hermes Python 3.11 paths exported through PYTHONPATH, launch Browser Use installed as a Python 3.12 uv tool. Before this fix, startup imports Pydantic from the wrong venv and fails in pydantic_core.
2. Run scripts/run_tests.sh tests/tools/test_browser_use_cli.py tests/tools/test_browser_use_session_expiry.py -q.
3. Launch a fresh Hermes Desktop backend and use browser_exec to navigate to https://example.com, then evaluate document.querySelector("h1").textContent.

Verified locally:

• 82/82 targeted Browser Use tests passed.
• Ruff, py_compile, and git diff --check passed.
• Browser Use doctor reported Chrome, daemon, and active browser connection healthy.
• Live restarted Desktop browser_exec loaded Example Domain and extracted the expected DOM heading.

Checklist

Code

• I have read the Contributing Guide.
• My commit follows Conventional Commits.
• I searched existing issues and PRs to make sure this is not a duplicate.
• This PR contains only changes related to this fix.
• All required GitHub CI checks pass, including 12 Python slices, macOS, Windows, lint/type, E2E, security, attribution, and Docker amd64/arm64.
• I added a regression test for the bug.
• Tested on macOS 27.0 with Hermes Python 3.11.15 and Browser Use Python 3.12.13.

Documentation & Housekeeping

• Relevant documentation is N/A; the subprocess contract is documented in the function docstring.
• cli-config.yaml.example changes are N/A.
• CONTRIBUTING.md / AGENTS.md changes are N/A.
• Cross-platform impact was considered: environment key removal uses portable dictionary operations before subprocess.run.
• Tool description/schema changes are N/A; user-facing behavior is unchanged except that Browser Use starts successfully.

Screenshots / Logs

Live post-restart verification returned:

https://example.com/ — 🐴 Example Domain
document.querySelector("h1").textContent -> Example Domain

[alt-glitch]

This was generated by AI during triage.

Duplicate of #83471. Both patches remove PYTHONPATH and PYTHONHOME at the Browser Use subprocess boundary to prevent the same cross-Python ABI import failure; #83471 is the earlier open implementation.

[d31tcjg]

Confirmed as a duplicate of #83471. Both changes strip PYTHONPATH and PYTHONHOME in _base_subprocess_env() to prevent the same cross-Python ABI import failure. Since #83471 is the earlier implementation and closes #83427, I am closing this PR in its favor. This PR’s regression test and successful CI/live Desktop validation remain available if useful. Thank you for the triage.