Atlas Treasury — from spec to a live fintech app with real PayPal APIs in 4 days (28 Oct → 1 Nov 2026). Problem: a company run by AI agents needs agents to earn and spend money safely. Built: PayPal Invoicing, Orders v2, Payouts, Webhooks and Disputes (sandbox) wired end to end; a policy engine in code with per-agent budgets — anything above policy waits for one tap on the owner's phone; a ledger linking every money movement to the task that caused it; Claude agents propose, code enforces the money rules. Numbers: ~2,300 lines of app code, 69 automated tests, 5 PayPal APIs, live URL. Code (MIT): github.com/iphoter-kolosov/atlas-treasury · video: youtu.be/RL5RwFmiSlc