Done. I've written the forecast change note to `output/drivers-note.md`.

**Summary of changes:**
- **EBITDA declined ($149K) or 32.9%** from $452K (Prior) to $303K (Current)
- **Active customers** fell from 46 to 44 (all 12 months), driving the largest loss of ($133K)
- **Headcount** increased 0.75 FTE over 9 months, costing ($54K)
- **Gross margin** improved 40 basis points all year, partially recovering $39K
- Revenue per customer, Cost per head, and Other opex were unchanged

The note includes the walk table, changed drivers summary, and review bullets asking which assumptions support each of the three driver changes that moved the forecast.