[engine-failure] PROJ-837-llmxive-follow-up-extending-moebius-0-2b @ tasks: RuntimeError

Automated report (spec 023 / FR-016) — an unexpected engine failure occurred while processing **PROJ-837-llmxive-follow-up-extending-moebius-0-2b** 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: tasked\nartifact_path: projects/PROJ-837-llmxive-follow-up-extending-moebius-0-2b/specs/001-llmxive-follow-up-extending-moeb'
```

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 examining the review artifact under projects/PROJ-837-llmxive-follow-up-extending-moebius-0-2b/specs/001-llmxive-follow-up-extending-moebius-0-2b and the engine path that processes it at the tasks stage. Reproduce the retry and trace how the constraint_preservation review frontmatter is validated. Done means a truncated or contentless review cannot count as acceptance and the normal retry completes without this RuntimeError.

Written by the indexing model from the issue text.