It was all GitHub Spec Kit + Claude Opus tbh. I narrated a couple paragraphs of how I wanted to sync to flow and it knocked it out in one pass practically.
It's great because Claude Code generated complex analysis/models 10X better than I was familiar with.
The key was normalizing the payee/categories so we can analyze month to month, and separating fixed vs variable spend. It then did a fancy Monte Carlo simulation with the computed mean/stddev per payee. And out came T+30/T+60 estimates at P50/P80/P90.
How well has the cash flow prediction worked?