[engine-failure] PROJ-258-the-effect-of-simulated-social-rejection @ tasks: RuntimeError

Automated report (spec 023 / FR-016) — an unexpected engine failure occurred while processing **PROJ-258-the-effect-of-simulated-social-rejection** at stage `tasks`.

```
RuntimeError: LLMReviewer[executability]: review frontmatter has neither `verdict:` nor `concerns:`/`action_items:` — a contentless/truncated review MUST NOT count as acceptance (false-convergence guard). First 200 chars: '```yaml\n---\nreviewer_name: rq_validity\nreviewer_kind: llm\nstage: tasks\nartifact_path: projects/PROJ-258-the-effect-of-simulated-social-rejection/specs/001-the-effect-of-simulated-social-rejection/task'
```

The project remains schedulable; it will retry on its normal cadence and recover once the underlying defect is fixed. Closing this issue does not require any project-state change.

Start at the LLMReviewer executability handling for the tasks stage and reproduce the failure from spec 023 / FR-016 using the PROJ-258 review artifact. Trace how review frontmatter is parsed when it contains neither verdict nor concerns/action_items. Done means the automated report no longer produces this unexpected engine failure and contentless or truncated reviews cannot count as acceptance.

Written by the indexing model from the issue text.