fix(browser): pass current agent-browser sandbox args

[EmpireOperating]

Summary

• pass sandbox bypass flags through AGENT_BROWSER_ARGS, which is what current agent-browser versions read
• keep AGENT_BROWSER_CHROME_FLAGS as a backward-compatible fallback for older agent-browser builds
• include Arch Linux in the sandbox-bypass detection path for the observed Chrome early-exit/DevToolsActivePort failure mode
• add regression coverage for the subprocess environment passed to agent-browser

Test plan

• .venv/bin/python -m pytest -q tests/tools/test_browser_homebrew_paths.py tests/tools/test_browser_cdp_override.py tests/tools/test_browser_hardening.py
• git diff --check

Context

origin/main already injects --no-sandbox for root/AppArmor cases, but it currently writes only AGENT_BROWSER_CHROME_FLAGS. Current agent-browser uses AGENT_BROWSER_ARGS, so the injected flags can be silently ignored and local browser startup can fail before DevToolsActivePort is written.

[EmpireOperating]

Rebased this branch onto current main (674fad1) and resolved the browser-tool conflict.

Local validation from the rebased head (a0f2142):

• git diff --check
• .venv/bin/python -m py_compile tools/browser_tool.py tests/tools/test_browser_homebrew_paths.py
• .venv/bin/python -m pytest -q tests/tools/test_browser_homebrew_paths.py tests/tools/test_browser_chromium_check.py -o 'addopts=' → 41 passed

CI notes after the rebase:

• Passing: attribution, supply-chain scan, e2e, nix ubuntu, nix macos.
• ruff + ty diff failed while posting the PR comment from a fork (Resource not accessible by integration). The report body showed ruff clean and diagnostics in run_agent.py, not this PR's touched files.
• The full test job is still red, but the reported failures are outside this PR's changed files (tools/browser_tool.py, tests/tools/test_browser_homebrew_paths.py).

[teknium1]

Thanks for the focused diagnosis and regression coverage.

Automated hermes-sweeper review found that the sandbox-bypass behavior targeted here is already implemented on current main:

• tools/browser_tool.py:2405-2416 now injects AGENT_BROWSER_ARGS=--no-sandbox,--disable-dev-shm-usage when the root/Docker/AppArmor bypass predicate applies.
• Commit 8ed2ef6f46e9642acfba57b4b8da893a574ecfd0 made the AGENT_BROWSER_CHROME_FLAGS → comma-separated AGENT_BROWSER_ARGS correction.
• Commit 4695d2716f60da89152bdc9dfa7d96e54ea7c22e added the pre-set AGENT_BROWSER_ARGS guard and documentation.
• The fix shipped in v2026.5.16.

The linked competing-PR discussion also identifies this as the same env-var fix. Closing as implemented on main.