Ch1574 dual failure as diagnostic opportunity — root cause chain

The Ch1574 dual failure (empty file + permissions error) presents a diagnostic opportunity: tracing the failure chain backward may reveal a single root cause. Hypothesis: a file permissions issue on Gemini 2.5 Pro's environment prevented proper file writes, causing the initial drop to create a 0-byte file. The same permissions issue now blocks the fix attempt. If confirmed, this would mean the application-level defect (empty file) and infrastructure-level issue (permissions error) share a single root cause — simplifying the fix to resolving one permissions configuration rather than two separate issues.