What does this PR do?

Allows operators to control subprocess HOME isolation explicitly. This keeps the default isolated behavior while adding environment switches for disabling isolation or overriding the subprocess HOME path when a deployment needs a specific home directory.

Related Issue

N/A.

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

• Add HERMES_PROFILE_HOME_ISOLATION=0|false|no|off support for disabling subprocess HOME isolation.
• Add HERMES_SUBPROCESS_HOME=/path support for explicit subprocess HOME override.
• Preserve the existing default profile-home isolation behavior.
• Ensure HERMES_SUBPROCESS_HOME takes precedence over the isolation-disable flag.
• Scrub the new environment variables in tests to avoid cross-test contamination.
• Add regression coverage for default isolation, disable behavior, explicit override, and precedence.

How to Test

1. Run subprocess HOME isolation focused tests.
2. Run related config/environment isolation tests.
3. Verify HERMES_SUBPROCESS_HOME precedence over HERMES_PROFILE_HOME_ISOLATION=0.
4. Run a read-only Codex review of the final branch delta.

Verification performed during refresh:

• uv run --extra dev pytest ... focused subprocess/profile tests: 130 passed.
• Read-only Codex review: first BLOCKED → fixes applied → fresh final review VERDICT: CLEAN.
• Branch was rebased onto current main and updated with --force-with-lease.

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature (no unrelated commits)
• I've run pytest tests/ -q and all tests pass
• I've added tests for my changes (required for bug fixes, strongly encouraged for features)
• I've tested on my platform: macOS

Note: I ran focused/regression tests locally for the changed subprocess HOME behavior and am relying on GitHub Actions for the full matrix.

Documentation & Housekeeping

• I've updated relevant documentation (README, docs/, docstrings) — or N/A
• I've updated cli-config.yaml.example if I added/changed config keys — or N/A
• I've updated CONTRIBUTING.md or AGENTS.md if I changed architecture or workflows — or N/A
• I've considered cross-platform impact (Windows, macOS) per the compatibility guide — or N/A
• I've updated tool descriptions/schemas if I changed tool behavior — or N/A

For New Skills

N/A — this PR does not add a skill.

Screenshots / Logs

N/A. Relevant verification is in local focused test output, Codex review logs, and GitHub Actions checks.