fix(quality): register visionBridge-responses-9597 covering test in stryker tap.testFiles

[hartmark]

Summary

• Registers tests/unit/guardrails/visionBridge-responses-9597.test.ts in stryker.conf.json's tap.testFiles — it covers open-sse/services/combo/comboStructure.ts but was missing from the list, so its mutant kills weren't counted.

Root cause

check-mutation-test-coverage.mjs --strict (the mutation-test-coverage gate in Fast Quality Gates) scans all unit test files for ones that exercise a mutated module and asserts every one of them is registered in tap.testFiles. This one covering test drifted out of sync — currently failing this gate on every open PR against release/v3.8.50, unrelated to whatever else the PR touches. Reproduced on the pure tip (6143da70d1) before this fix.

Validation

• node scripts/check/check-mutation-test-coverage.mjs --strict — clean (was failing before)
• node --import tsx --test tests/unit/guardrails/visionBridge-responses-9597.test.ts — 5/5 pass
• python3 -c "import json; json.load(open('stryker.conf.json'))" — valid JSON

Tests Added Or Updated

• None — this registers an existing test, no behavior change.

Coverage Notes

• N/A, config-only change.

Reviewer Notes

• Found while investigating base-red failures on feat(responses): virtualize previous_response_id continuation regardless of upstream support #10262 and feat(dashboard): agentic conversation tracking — v4, decoupled + storage-architecture concern resolved #10263 — this was the only one of four failing gates with no existing tracking issue or PR (the others are covered by 🔴 Release branch not green: release/v3.8.50 #9985 (dead-code, tracked as expected ratchet drift), and [TS7] fix(types): remove duplicate SSE comment import #10252/fix(ci): clear base-reds on release/v3.8.50 (round 4) #10260 (open-sse-typecheck stream.ts TS2300, poolside catalog test)).

[hartmark]

Verified against current release/v3.8.50 (20ea78c94): stryker.conf.json's tap.testFiles already includes tests/unit/guardrails/visionBridge-responses-9597.test.ts (line 237) — this landed upstream through a different path since this PR was opened. Rebasing this branch drops the commit as redundant (patch contents already present), leaving zero diff. Closing as superseded.