[engine-failure] PROJ-833-llmxive-follow-up-extending-perceptiondl @ tasks: RuntimeError

Automated report (spec 023 / FR-016) — an unexpected engine failure occurred while processing **PROJ-833-llmxive-follow-up-extending-perceptiondl** 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-833-llmxive-follow-up-extending-perceptiondl/specs/001-llmxive-follow-up-extending-perceptiondl/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 by tracing the tasks-stage LLMReviewer executability review and how its review frontmatter is parsed. Reproduce the reported RuntimeError using the PROJ-833 follow-up artifact, then verify that a review without verdict, concerns, or action_items is rejected and cannot count as acceptance.

Written by the indexing model from the issue text.