## Why

Executor Structured Output V2 已经完成 Executor、Gatekeeper、Verifier、Composer 四段主链路改造，但现有离线评测仍主要检查最终答案关键词、证据工具覆盖和 Verifier verdict。阶段 5 需要把新增的审计字段纳入固定回归门禁，证明 `Planner -> Executor -> Gatekeeper -> Verifier -> Composer -> final answer` 链路不是只在单次 demo 中可用。

## What Changes

- Extend the diagnosis eval harness so V2 audit fields are validated as first-class regression checks.
- Add fixture coverage for Gatekeeper failure, claim verification filtering, Composer fallback, and raw JSON leakage prevention.
- Update baseline reports to reflect the expanded fixed fixture set.
- Update eval documentation so another agent can understand the background, stages, data fields, and acceptance commands.
- No production protocol change is intended in this phase; production chain behavior should remain unchanged unless tests reveal a bug.

## Capabilities

### New Capabilities

- None.

### Modified Capabilities

- `diagnosis-eval-harness`: add V2 audit-closure requirements for Gatekeeper, Verifier claim checks, Composer output, and final-answer consistency.

## Impact

- Affected code:
  - `src/main/java/com/superbiz/agent/eval/*`
  - `src/test/java/com/superbiz/agent/eval/*`
- Affected data:
  - `mvp/eval/cases/diagnosis-cases.json`
  - `mvp/eval/fixtures/*.json`
  - `mvp/eval/reports/baseline-report.*`
  - `mvp/eval/schema.md`
  - `mvp/eval/README.md`
- Verification:
  - focused evaluator tests
  - relevant Executor/Gatekeeper/Verifier/Composer integration tests
  - OpenSpec validation and archive