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Articles & notes

Writing on backend, architecture and product development.

Testing · Fixtures · Automatización industrial · Falsos verdes

The green that proved nothing

I built a system that decides whether an industrial migration can be quoted at a fixed price. Its suites were green for days over data no user could have produced. Four ways of passing without having checked anything.

Agentes de IA · Observabilidad · Medición · Costes

Measuring what an agent costs is an accounting problem

I built a local meter to find out what AI agents cost me. The four traps I hit were not AI traps: they were accounting traps. Cumulative totals that must not be summed, cache counted twice, and filters cutting in the wrong place.

Fintech · Ledger · Arquitectura · Idempotencia

Money never moves twice

A transactional backend does not fail the day it goes down. It fails the day it works twice. Idempotency, double-entry and consistency when one operation crosses three systems that share no transaction.

IA · Fintech · Ledger

What an AI agent must not decide

I build payment systems with AI agents every day. What it taught me most is not what they can do — it is where I do not let them decide.