fix(browser): add termux PATH fallbacks

[adybag14-cyber]

What does this PR do?

This PR fixes browser_tool on Android/Termux by restoring the Termux-specific PATH entries needed by agent-browser subprocesses.

Before this change, browser command discovery and subprocess execution used different fallback PATH logic. The subprocess path rebuild only included Homebrew/system directories, so it dropped Termux paths like /data/data/com.termux/files/usr/bin and /data/data/com.termux/files/usr/sbin. On Android, that breaks the agent-browser → grun handoff and causes browser commands to fail even when the required binaries are installed.

This fix keeps the change minimal and targeted:

• add Termux fallback PATH directories alongside the existing Homebrew/system fallbacks
• centralize browser PATH fallback assembly so discovery and subprocess execution use the same logic
• add focused regression tests covering Termux fallback lookup and subprocess PATH propagation

Related Issue

Fixes #5845

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

• tools/browser_tool.py
  • added Termux PATH fallback directories
  • introduced shared browser PATH helpers used by both CLI discovery and subprocess execution
  • updated _find_agent_browser() to search the merged fallback PATH
  • updated _run_browser_command() to build subprocess PATH from the same merged helper
• tests/tools/test_browser_homebrew_paths.py
  • added regression coverage for Termux fallback dirs in _SANE_PATH
  • added regression coverage for npx discovery via Termux fallback dirs
  • added regression coverage for subprocess PATH propagation on Termux

How to Test

1. On Termux/Android, ensure agent-browser and its Android runtime dependencies are installed.
2. Run:
   source /data/data/com.termux/files/home/.hermes/hermes-agent/.venv/bin/activate && python -m pytest tests/tools/test_browser_homebrew_paths.py -q
3. Verify the new Termux-specific tests pass and that browser subprocess PATH construction includes /data/data/com.termux/files/usr/bin.

Screenshots / Logs

Targeted validation run:

• 21 passed in 1.82s

@gut-puncture

[adybag14-cyber]

@kaan-escober

[teknium1]

Thanks for this contribution, @adybag14-cyber! The Termux PATH fix has already landed on main and shipped.

Automated hermes-sweeper review found that this PR's changes are already implemented:

• _SANE_PATH_DIRS with Termux entries (/data/data/com.termux/files/usr/bin, /data/data/com.termux/files/usr/sbin) — tools/browser_tool.py line 99
• _browser_candidate_path_dirs() and _merge_browser_path() helpers centralizing PATH construction
• Both _find_agent_browser() and _run_browser_command() using _merge_browser_path()
• Regression tests in tests/tools/test_browser_homebrew_paths.py covering all three scenarios

All of this landed in commit 56c34ac (fix(browser): add termux PATH fallbacks, cherry-picked from PR #9846) and shipped in v2026.4.16. Closing as implemented_on_main.