Software Systems Engineer — financial infrastructure · distributed systems · reliability
I work on the part of software where consistency, traceability and failure behaviour decide whether the system is correct: payment rails, wallets, double-entry ledgers and reconciliation. Most of it has to keep moving real money while it is being changed, which is the constraint that shapes how I design: idempotent writes, explicit unknown states, invariants that run, and a migration path that never asks the business to stop for a weekend.
I choose tools per problem rather than per résumé. The projects below are in Go, Rust, TypeScript and PHP because that is what each of them needed.
| Project | What it does | Stack |
|---|---|---|
| agentic-assurance / EXORYN | Assurance layer between an AI-generated financial intent and execution: verifies actor identity, spend authority, deterministic policy, replay, and durable evidence before the action proceeds. Not a trading bot; V0 is paper-execution only. | Go · Next.js · PostgreSQL · NATS JetStream · ClickHouse |
| controlshift | Preflight for legacy PLC migrations: reads an Allen-Bradley program plus the client's incomplete documentation and emits scope, unknowns and a three-level pricing verdict. A separate deterministic engine, versioned rule packs, golden cases, and UNKNOWN as a first-class state. |
Rust · NestJS · PostgreSQL · Next.js · Python |
| agent-engine | Local-first, read-only dashboard for what AI coding agents actually cost — tokens, spend and activity across Claude Code, Cursor, Codex and OpenCode. No telemetry, no cloud, incremental ingestion, normalised cost model. | Bun · TypeScript · SQLite |
| wooops-auditor | Read-only operational diagnostics for WooCommerce stores. Inspects and reports; never writes to the store. | PHP |
Engineering notes, mostly about money that must not be counted twice — alexander.sanchezavila.com/blog
- El dinero no se mueve dos veces — idempotency in payment systems
- Una reserva es un asiento — modelling holds and releases as ledger entries
- El verde que no probaba nada — four passing suites over a broken system
- Migrar sin apagar — shadow-first migration of a live financial monolith
- Lo que un agente de IA no puede decidir — where the guardrails go
Financial infrastructure · Payment systems · Wallets & double-entry ledgers · Reconciliation · Distributed systems · Reliability & data integrity · Backend architecture · Developer tooling
Languages used in real projects: Go · Rust · TypeScript/JavaScript · PHP · Python · SQL
- Portfolio and case studies — alexander.sanchezavila.com
- LinkedIn — alexander-sanchez-torrejano
Spanish is my working language; I write and read technical English. Open to conversations about systems where correctness is not negotiable.