ROOT CAUSE: Spark cleans up files after test completes (even on failure).
By the time we try to download, files are already deleted.
SOLUTION: Monitor test logs in real-time and download file THE INSTANT
we see the EOF error (meaning file exists and was just read).
Changes:
1. Start tests in detached mode
2. Background process monitors logs for 'EOFException.*78 bytes'
3. When detected, extract filename from error message
4. Download IMMEDIATELY (file still exists!)
5. Quick analysis with parquet-tools
6. Main process waits for test completion
This catches the file at the exact moment it exists and is causing the error!