test(disk-hygiene): mock sys.argv in run_guard* helpers to seal the kill-switch argv seam

[kyle-sexton]

Lane: work-2. Source: #968 security-review SUGGESTION (medium confidence, non-blocking).

Triggering example: in plugins/disk-hygiene/skills/clean/scripts/test_hygiene.py, the helpers run_guard, run_guard_disabled, and run_guard_powershell_disabled patch os.environ but NOT sys.argv.

Observed: after #382, resolve_disk_hygiene_enabled() reads sys.argv[1:] before the env fallback. If a test runner's argv happened to contain --disk-hygiene-enabled true, it would override the env-var mock and a run_guard_powershell_disabled-based test would see ask instead of the expected deny. Standard invocations (python -m unittest, pytest) never produce such argv, so CI is unaffected today — this is latent fragility, not a live failure.

Expected: apply the pattern the new run_guard_enabled_argv helper already demonstrates — mock sys.argv alongside os.environ in the three older helpers — to fully isolate the argv seam.

Category: test-coverage (improvement). Not fail-open; the underlying fix is correct and security-reviewed clean.

[kyle-sexton]

This was generated by AI (triage-decide lane — intake routing).

Routed status: ready (simple; zero design decisions). Verified on origin/main: the pattern helper run_guard_enabled_argv (line ~1087) and all three target helpers (run_guard ~1061, run_guard_disabled ~1074, run_guard_powershell_disabled ~1312) are present; the referenced #968 and #382 are both merged, so no open prerequisite.

Fix (single file, plugins/disk-hygiene/skills/clean/scripts/test_hygiene.py): mock sys.argv alongside os.environ in the three older helpers, mirroring the argv-isolation the existing run_guard_enabled_argv helper already applies, so resolve_disk_hygiene_enabled()'s sys.argv[1:] read can't leak the runner's argv into the mocked env fallback. Acceptance: the three helpers pin sys.argv (e.g. to a bare program name) and remain green under python -m unittest / pytest.

Category: test-coverage (improvement) — latent fragility, not fail-open (the underlying #382 fix is correct and security-reviewed clean). priority: medium.

[kyle-sexton]