BR-CO-13 — Totals that drift from the lines

Cached totals drift to the cent when a template recomputes only one of the three figures. The gate recomputes every total from the lines and reports the exact delta.

• Recomputes BT-106 / BT-109 / BT-110 / BT-112 from the lines and reports the drift delta.
• Names the specific read rule that failed (BR-CO-10 through BR-CO-17) with its field path.
• Applies the destination country's VAT rounding rule (per line vs at the total).