Debug output

After answer extraction, Sunbeam attempts to write a JPEG overlay to:

./data/debug/debug_grid_<original-filename>_<timestamp>.jpeg

The image starts as a clone of the aligned image. Each detected filled bubble is outlined in green before the file is written. If the uploaded part has no original filename, the name segment is unknown.

The write is best-effort: its exception is swallowed. The repository does not configure the directory, redact images, rotate files, delete old files, or define a retention period. Debug output should therefore be treated as potentially sensitive sheet data and disabled or access-controlled by deployment policy until the application provides controlled handling.