[engine-failure] PROJ-921-llmxive-follow-up-extending-achieving-go @ plan: RuntimeError

Automated report (spec 023 / FR-016) — an unexpected engine failure occurred while processing **PROJ-921-llmxive-follow-up-extending-achieving-go** at stage `plan`.

```
RuntimeError: LLMReviewer[plan_consistency]: 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: plan_consistency\nreviewer_kind: llm\nstage: planned\nartifact_path: projects/PROJ-921-llmxive-follow-up-extending-achieving-go/specs/001-llmxive-follow-up-extending-achieving-'
```

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 plan-stage LLMReviewer[plan_consistency] handling for the review frontmatter in spec 023 / FR-016 and the PROJ-921 artifact path shown in the report. Determine why a truncated or contentless review produces an engine failure instead of being safely rejected; done means the normal retry cadence can recover without counting the review as acceptance.

Written by the indexing model from the issue text.