[quality] pullRequestOwners.ts: the draft/labels defaults test is vacuous, and the file dedupe and repository-keyed memos survive deletion under both suites #532

Finding

src/utils/pullRequestOwners.ts is at 100 % lines/branches under both suites (npm run test:coverage and npm run test:coverage:e2e on main @ 88241f4, local runs), but a hand mutation probe shows four behaviours no test observes. Each mutant was applied to src/, then run against (a) npx vitest run __tests__/utils/pullRequestOwners.test.ts __tests__/utils/ownersAuth.test.ts __tests__/plugins and (b) npm run pack + npx vitest run __tests__/bundle (502 tests). All four pass both:

open: pull.state === 'open' → !== 'closed' also survives, but GitHub's state is only open/closed, so that mutant is equivalent and is not counted.

Evidence

• Unit: npm run test:coverage on 88241f4 — src/utils/pullRequestOwners.ts 100 % lines / 100 % branches; the four mutants above each leave Tests 394 passed (394) on the selector in (a).
• E2E: npm run test:coverage:e2e on 88241f4 — same file 100 % / 100 %; each mutant repacked into dist/index.js leaves Tests 502 passed (502) on __tests__/bundle.
• Both suites cover every line and branch, so this is an assertion-strength finding, not a coverage gap; priority follows "surviving under both suites".

Recommendation

One PR against __tests__/utils/pullRequestOwners.test.ts:

• make the defaults test actually omit user, draft, state, requested_reviewers, assignees, labels (pass undefined overrides so JSON drops the keys) and assert draft: false, open: false, labels: []
• a positive draft: true, state: 'open' → { draft: true, open: true } and state: 'closed' → open: false case
• a rename whose previous_filename another entry reuses → the path appears once in files and perFile.size is 2
• a second MockContext for another repository: same pull number is fetched again, and the same branch name is read again

The memo keys cannot be pinned from dist/index.js (one repository per process), so this stays a unit-suite fix; the e2e routeOwners helper only serves string filenames, so the rename case stays unit-side too.

Priority

• Impact: medium — loadPullRequestOwners feeds approve, approveReview, blunderbuss and owners-label; a wrong draft fold would let /approve act on drafts, and a duplicated path would double-count coverage in approve's per-file loop
• Effort: low

Filed by quality agent (hold-gated mode)

🐝 Hive Agent: quality | Instance: hosted-available-lke648397-260827-5q9t | SHA: 88241f4

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