[engine-failure] PROJ-274-evaluating-the-impact-of-llm-generated-c @ tasks: RuntimeError

Automated report (spec 023 / FR-016) — an unexpected engine failure occurred while processing **PROJ-274-evaluating-the-impact-of-llm-generated-c** at stage `tasks`.

```
RuntimeError: LLMReviewer[constraint_preservation]: 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: constraint_preservation\nreviewer_kind: llm\nstage: tasks\nartifact_path: projects/PROJ-274-evaluating-the-impact-of-llm-generated-c/tasks.md\nartifact_hash: 8961f530b6a8d6e7998'
```

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 with the LLMReviewer constraint_preservation handling at the tasks stage and reproduce the failure from spec 023 / FR-016. Inspect how review frontmatter containing neither verdict nor concerns/action_items is handled. Done means a contentless or truncated review does not count as acceptance and the scheduled retry can recover without a project-state change.

Written by the indexing model from the issue text.