Previously updateBatchStatus wrote the batch-level total recordCount to
every row, causing the detail view to show misleading identical counts.
Now mergeFiles collects per-order material counts, the handler writes
each order's count individually via updateRecordStatus, and batch
aggregation uses SUM instead of MAX for accurate totals.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>