[engine-failure] PROJ-734-detecting-distribution-shift-in-public-h @ tasks: RuntimeError

Automated report (spec 023 / FR-016) — an unexpected engine failure occurred while processing **PROJ-734-detecting-distribution-shift-in-public-h** 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-734-detecting-distribution-shift-in-public-h/specs/001-detecting-distribution-shift-in-p'
```

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 handling for LLMReviewer[constraint_preservation] and the review frontmatter validation described in the report. Reproduce the failure if possible, then verify that a truncated or contentless review no longer causes an engine failure and that the project remains schedulable for retry.

Written by the indexing model from the issue text.