machine-health: Get-CisaKevCache skips refresh when the cache file is empty or whitespace

[kyle-sexton]

Context

Found by the repo-wide /code-tidying:batch-simplify sweep (62 groups / 986 files, branch claude/repo-code-tidying-batch-twhddw). The sweep's doctrine files latent defects instead of fixing them mid-sweep, because the fix changes observable behavior; this issue is that filing.

plugins/machine-health/skills/audit/scripts/windows/lib/Get-CisaKevCache.ps1:51-75 — an empty/whitespace cache file leaves needsRefresh false, unlike every other malformed-cache path, so a truncated cache never self-heals.

Proposed work

• Treat empty/whitespace cache content as malformed (needsRefresh = true).

Acceptance criteria

• An empty cache file triggers a refresh in the test fixture.

References

• plugins/machine-health/skills/audit/scripts/windows/lib/Get-CisaKevCache.ps1:51-75

Filed by the /code-tidying:batch-simplify closeout (Phase 8).