[quality] plugins: cover the untested error and fallback branches of lgtmBinding, ownersLabel and requireMatchingLabel #203

Finding

npm run test:coverage on origin/main 187c5e3 leaves five error/edge branches in three plugins unexercised:

• src/plugins/lgtmBinding.ts:177 — sender?.login ?? 'unknown' and the pull_request?.html_url fallbacks when the labeled payload carries neither (the status is still bound, described as lgtm by unknown).
• src/plugins/ownersLabel.ts:70 — could not list the repository labels: … when GET /repos/:o/:r/labels fails.
• src/plugins/requireMatchingLabel.ts:184 — github context payload missing issue or pull request when the payload has neither.
• src/plugins/requireMatchingLabel.ts:245 — could not list comments: … when GET /issues/:n/comments fails, surfaced as require-matching-label needs-kind: ….
• src/plugins/requireMatchingLabel.ts:248 — a bot comment with body: null is treated as unmarked (nothing deleted).

Unit evidence: npx vitest run --coverage @ 187c5e3 — lgtmBinding.ts 96.29% branches, ownersLabel.ts 97.14% lines, requireMatchingLabel.ts 97.7% lines / 95.38% branches. End-to-end evidence: the repository has no integration or e2e suite — .github/workflows/test.yml runs only npm run test:coverage — so unit coverage is the sole coverage source.

Recommendation

Add __tests__/plugins/pluginErrorPaths.test.ts with one msw-served test per branch, using the fixtures the existing lgtmBinding.test.ts / ownersLabel.test.ts / requireMatchingLabel.test.ts already use. Result: lgtmBinding.ts and ownersLabel.ts 100% lines and branches; requireMatchingLabel.ts 100% lines, 98.46% branches (only the non-Error rejection at line 167 remains).

Disjoint from every open hold-gated PR (#173–#202): none touches __tests__/plugins/{lgtmBinding,ownersLabel,requireMatchingLabel}.test.ts or a new file under __tests__/plugins/.

Priority

• Impact: medium — the five branches are the operator-facing error messages for label listing, comment listing and malformed payloads; a regression there fails the run with a raw octokit error instead of the named cause.
• Effort: low

Filed by quality agent (hold-gated mode)

🐝 Hive Agent: quality | Instance: hosted-available-lke648397-260827-5q9t | SHA: 187c5e3

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