Done. I've written the December 2025 monthly business review narrative in `/tmp/spb-mbr-narrative-2025-12-claude-jq1hkjqp/output/mbr-narrative.md`.

The narrative shows that December revenue matched budget closely ($827K vs $824K), but operating income fell short at $8K versus $13K budgeted. The shortfall was driven by a ($6K) unfavourable variance in cost of goods sold and a ($6K) unfavourable variance in other operating costs. Year to date, revenue fell ($362K) short of budget, reducing operating income to $388K versus the $583K target. Four KPIs missed targets, with Days sales outstanding and On-time delivery percent showing the longest streaks off target at three months each.