test(metrics): cover validate-metrics optional-section branches

[kubestellar-hive]

Test Improvement

Adds 14 fixture-driven cases to tests/validate-metrics.test.mjs covering scripts/validate-metrics.mjs validation outcomes that were never exercised:

• metric with an absent id, and metric with a null value
• empty metrics array (accepting path)
• omitted entry missing id
• lifecycle card with a non-finite value; lifecycle omission missing reason; fully-populated valid lifecycle
• time series missing sourceUrl; series point with a non-finite value; fully-populated valid series
• breakdown whose values is not an array; breakdown missing its label; non-finite breakdown value; fully-populated valid breakdown

These are the guards that only run when a metrics file carries the optional referenceArchitectureLifecycle, series, or breakdown sections. data/metrics.json is a generated artifact, so a partially-written regeneration is precisely what they exist to catch.

Each case asserts the specific exit status and the specific validator error string for its branch, and the valid-section cases pin the accepting path, so the tests fail loudly if a guard is removed or its message drifts.

Tests only — no production code is changed. Suite goes from 55 to 69 passing tests (node --test, node v26.8.2), rebased on current main.

Note on the coverage number

The reported branch percentage for scripts/validate-metrics.mjs will not move when these land. tests/helpers.mjs runScriptWithFixtures runs a temp-dir copy of the script in a subprocess, which node --test coverage instrumentation does not attribute back to the repo path. The evidence of added coverage here is behavioral, not a percentage. That measurement limitation is tracked separately and is not something this PR tries to fix.

Related Issue

Closes #262 (merging this adds every test the issue asks for, leaving nothing further for it to track)

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Filed by quality agent (hold-gated mode). Human review required.

— hive: agent=quality backend=copilot model=claude-opus-5

[kubestellar-hive]

Important

Held for human review by the hive's ACMM level gate.

This PR was opened by the "quality" agent while Hive policy required a human checkpoint for that agent. Non-outreach agents are held at ACMM L3–L5; the outreach agent is always held because it publishes project-facing communication.

Hive will automatically remove the hold label once current policy no longer requires a level hold for "quality". If this is an outreach PR, a human must review it and remove the label.