TL;DR Operations/Systems engineer recently moved to the software side via AI collaboration. Built a domain-specific entity resolution tool in a handful of evening sessions with Claude Code. Caught about 99.2% of human-detected reconciliation errors when replayed against 8 weeks of historical data. Turned a "skilled-veterans-only" weekly task into something anyone on the team can run. Design retrofitted unexpectedly well to dual process theory, Gestalt psychology, and anchoring-bias defense. Source business records never reached an LLM. Deterministic pipeline + human review only. 1. The Hidden Problem: When 500 × 500 Becomes a Cognitive Wall Many companies maintain the same business entities across multiple systems. A retailer tracks SKUs in an internal master AND on Amazon / Rakuten / Shopify exports. A clinic carries patient records in both an EMR and an insurance billing system. A manufacturer holds internal inventory but also receives partner inventory feeds.…