[quality] cover the non-Error rejection and empty-config fallbacks in labelSync, lgtm, mergeQueue and issueComment/approve #222

Finding

Unit coverage on main @ c48bd6d (npm ci && npx vitest run --coverage, vitest v8 provider, reproducible locally; CI run of the same command in build-test on run 35910387179 prints the same table but publishes nothing, see #209) reports 99.83% statements / 98.35% branches. The remaining uncovered branches in four files form one cluster — the non-Error fallback of e instanceof Error ? e.message : String(e) plus two nullish/empty fallbacks — none of which any test reaches:

End-to-end evidence: the prow / prow check dogfoods the built dist/ on PRs but emits no coverage data (see #209), so no end-to-end coverage source exists to combine with; this finding is unit-only and the limitation is stated here rather than inferred.

src/utils/config.ts:603 (e instanceof Error ? e.message : e around parseDuration) is excluded on purpose: parseDuration only ever throws Error, so that branch is unreachable and not a test gap.

Disjoint from the open hold-gated PRs: #217 (__tests__/utils/auth.test.ts), #219 (__tests__/plugins/tideMergeQueue.test.ts, testUtils.ts), #221 (__tests__/plugins/approveEvents.test.ts).

Recommendation

Add one test per row to the existing test file of each module, stubbing the rejection where the github client can only ever produce an Error over HTTP:

• __tests__/cronJobTest/labelSync.test.ts: no-config debug line; newOctokit spy returning a client whose issues.createLabel rejects with a string
• __tests__/label/lgtm.test.ts: vi.mock(lgtmBinding, { spy: true }) with bindLgtm rejecting a string; assert the reply body and setFailed
• __tests__/utils/mergeQueue.test.ts: queueState with a graphql stub rejecting a string
• __tests__/issueCommentTest/approve.test.ts: require_self_approval with a payload whose issue has no user

Priority

• Impact: low — branch-only residue at 98.35%; the String(e) fallbacks decide what a user sees in the refusal comment / setFailed message when a plugin rejects with a bare value
• Effort: low

Filed by quality agent (hold-gated mode)

🐝 Hive Agent: quality | Instance: hosted-available-lke648397-260827-5q9t | SHA: c48bd6d

— hive: agent=quality backend=copilot model=claude-fable-5.1 copilot=1.0.88