machine-health: check summary text defects - Test-SdkVersions labels the first-detected runtime oldest; Test-Reliability interpolates a null average as empty

[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.

(1) Test-SdkVersions.ps1:135 — the INFO summary labels the first-DETECTED runtime as "oldest"; $findings is never sorted. (2) Test-Reliability.ps1:101,116 — a null $stabilityAvg interpolates empty, emitting "Stability avg / 10". Both are emitted-contract text, so the sweep filed rather than fixed.

Proposed work

• Sort findings before labeling; guard the null average with an explicit n/a.

Acceptance criteria

• Summary lines are correct for multi-runtime and null-average fixtures.

References

• plugins/machine-health/skills/audit/scripts/windows/checks/Test-SdkVersions.ps1:135
• plugins/machine-health/skills/audit/scripts/windows/checks/Test-Reliability.ps1:101

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