graph TD A[Start: Load download_log.json] --> B[Parse JSON to extract URL/MP4 pairs] B --> C{Process each MP4} C --> |For each entry| D[Extract First Frame] D --> E[Skill #202: Generate Thumbnail] E --> |Success| F[Save Thumbnail PNG] E --> |Error| G[Mark Status ERROR] F --> H[Mark Status OK] G --> I[Next Entry] H --> I I --> |More entries| C I --> |All done| J[Collect All Results] J --> K[Skill #223: Format Report] K --> L[Write integrity_report.txt] L --> M[End: Validation Complete]