fix(review): stop restating blockers twice in the PR review comment

[JSONbored]

Summary

• Confirmed on PR feat(miner): add schema-version migration runner across local stores #5347's live review comment: the "Blockers" bullet under "Suggested Action" and the "Why this is blocked" section further down showed byte-identical text.
• Root cause: gateVerdictReason() (src/review/unified-comment-bridge.ts) fell back to gate.summary for the top-level reason line. evaluateGateCheckCore's summary for a "failure" conclusion is literally gate.blockers restated as one joined string (title + — + action per finding, joined with "; "). The "Why this is blocked" section a few lines below independently renders those same gate.blockers (folded in via buildDualReviewNotes's gateBlockers param) — so a blocked/reject-close comment printed the identical blocker text twice.
• The existing test suite's gate() helper always hand-set a short, generic summary string ("A hard blocker was found.") rather than the realistic blockers-restated value evaluateGateCheckCore actually produces in production, so this slipped past every existing test.

Fix

gateVerdictReason now only falls back to gate.summary/gate.title when gate.blockers is empty. Structurally, evaluateGateCheckCore only ever returns a non-empty blockers array on a "failure" conclusion (every neutral/success branch explicitly sets blockers: []), so this is scoped precisely to the case that duplicates — the held/neutral case (which has no "Why this is blocked" section to duplicate against) is unaffected and still shows its own top-level reason exactly as before.

Test plan

• npm run typecheck — clean
• Added a regression test using the REALISTIC gate.summary shape (blockers restated), proving the blocker text now appears exactly once
• Added a coverage test confirming the held/neutral case (no gate blockers) is unaffected
• Updated one pre-existing test that had encoded the buggy duplicate-fallback behavior as an expected assertion
• npx vitest run test/unit/unified-comment-bridge.test.ts test/unit/unified-comment.test.ts test/unit/unified-comment-parity.test.ts — 170/170 passing
• npx vitest run test/unit/queue.test.ts test/unit/queue-2.test.ts test/unit/queue-3.test.ts test/unit/queue-4.test.ts test/unit/queue-5.test.ts (downstream comment-building callers) — 671/671 passing
• Targeted coverage run across all touching test files: src/review/unified-comment-bridge.ts is 100% lines / 99.6% branches (the one uncovered branch is on an untouched, pre-existing line, not part of this diff)
• npm run test:engine-parity — clean (this file isn't part of any hand-duplicated twin pair, confirmed)

[superagent-security]

Superagent didn't find any vulnerabilities or security issues in this PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.37%. Comparing base (a0639fd) to head (94f3b69).
⚠️ Report is 5 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5378      +/-   ##
==========================================
- Coverage   94.41%   94.37%   -0.04%     
==========================================
  Files         551      551              
  Lines       44168    44169       +1     
  Branches    14632    14633       +1     
==========================================
- Hits        41702    41686      -16     
- Misses       1791     1808      +17     
  Partials      675      675              

Flag	Coverage Δ
shard-1	43.76% <100.00%> (-0.38%)	⬇️
shard-2	34.14% <100.00%> (-0.41%)	⬇️
shard-3	32.18% <0.00%> (+0.63%)	⬆️
shard-4	31.22% <100.00%> (-0.06%)	⬇️
shard-5	33.11% <0.00%> (-0.21%)	⬇️
shard-6	43.62% <0.00%> (+0.21%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/review/unified-comment-bridge.ts	99.57% <100.00%> (+<0.01%)	⬆️

... and 1 file with indirect coverage changes

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