Federico Sapuppo

Ruby on Rails Developer

Senior Ruby on Rails developer and Rails core contributor. I built and operate Cross Ledger's proctored testing platform solo, a production Rails app developed with agent-assisted workflows. Lately I focus on agent orchestration and AI reliability engineering: evals, observability, harness design.

Co-founder at Cross Ledger
Ruby on Rails Contributor
Omarchy Contributor
Buenos Aires, Argentina (GMT-3)
Get in Touch View GitHub
Federico Sapuppo
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Technical Skills

AI Engineering

RailsPilot Mastra Agent Orchestration AI Reliability Engineering Evals & Observability Claude Code Hermes

Backend

Ruby on Rails Ruby PostgreSQL REST APIs Trailblazer

Frontend

HTML5 CSS3 JavaScript React Tailwind Bootstrap

DevOps & Cloud

AWS (EC2, ECS, RDS) Firebase Git GitHub GitLab

Testing & Tools

RSpec Capybara Sentry Jira Asana Notion

Open Source Contributions

Ruby on Rails Core
September 2024

Co-authored Rails Framework Enhancement

Co-authored a significant change to the Ruby on Rails framework that deprecated Sprockets as the default asset pipeline for new applications, establishing Propshaft as the new standard. This contribution involved updating test suites, removing legacy templates, and simplifying configuration files across the Rails codebase.

Commit: #52887 - No new apps should be started with sprockets
Impact: Affects all new Rails applications
Collaboration: Co-authored with 4 other contributors
View Contributor Profile View Commit on GitHub
Omarchy (Basecamp)
April 2026

T2 MacBook Support for DHH's Arch Linux Distribution

Contributed 5 merged PRs to Omarchy (DHH's opinionated Arch + Hyprland distribution), adding full T2 MacBook support. Fixes covered fan curves, keyboard backlight, battery indicator parsing, Bluetooth, and a migration script for existing installs. All shipped in Omarchy v3.5.0.

PRs Merged: #5132, #5135, #5137, #5145, #5176
Release: Shipped in Omarchy v3.5.0
Impact: Enables Omarchy on T2 MacBooks (2018–2020 models)
View Discussion T2 Customizations Repo
Linux Kernel (t2linux)
April 2026

Kernel Patch for Apple SMC Driver

Fixed a race condition in the applesmc kernel driver where 32-bit MMIO writes were clobbering adjacent single-byte registers, causing SMC command failures. Changed three iowrite32 calls to iowrite8, matching the ioread8 already used for the same registers.

PR: t2linux/linux-t2-patches#43
Impact: Fixes fan/thermal control on T2 MacBooks running Linux
Scope: 3-line kernel patch in applesmc driver
View PR on GitHub

Projects

Pretor

AI legal framework for law firms. A team of specialized agents that research official sources, draft filings, hold the case files, manage calendar and mail, and answer clients. Security by design: per-agent isolation, approval gates, and a hard rule against inventing the law.

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Cross Ledger

Recruiting platform for the accounting profession. Vetted, English-speaking accountants from Latin America, every candidate proctor-tested on a Rails platform I built and operate.

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Hermes

Marketing landing page for Hermes Agent, the self-improving AI agent by Nous Research. Built with modern web technologies.

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ARGPT

Argentine Portfolio Tracker: see your real USD return on assets bought with pesos, decomposed into stock vs. currency movement. Uses MEP/CCL rates.

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Contrarian Trifecta

Stock screening dashboard that surfaces contrarian DCA opportunities by combining fundamental quality, AI sentiment analysis, and technical floor detection.

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Cross Ledger

Founder
Co-founder & Engineer

Recruiting platform for the accounting profession

Cross Ledger connects US businesses with vetted, English-speaking accountants and bookkeepers from Latin America. One-time fee, six-month replacement guarantee, nearshore time zones.

Every candidate clears a proctored skills assessment before they reach a client. I built and operate that proctored testing platform myself: a production Rails application developed solo with agent-assisted workflows. The people we place are not just interviewed, they are tested under controlled conditions, by a system the founder engineers, monitors, and improves.

Vetting: Proctored skills testing on every candidate
Guarantee: 6-month replacement
Pricing: One-time placement fee
Talent: English-speaking, nearshore (Latin America)
Visit Cross Ledger

Work Experience

Ruby on Rails Developer

U.S. Medical Application (Freelance)

Jan 2026 - Present
  • Push Notifications: Replaced roughly 25 legacy email-only mailers with email and PWA web push using the Noticed and web-push gems, rolled out per cohort behind feature flags
  • Feature Flags: Introduced Flipper to gate PWA and notification features per program, replacing an environment-variable toggle with subdomain-scoped Flipper group gates
  • Production Bug Fix: Diagnosed and fixed web push subscriptions leaking between users on shared devices
  • Offline PWA: Built offline mode for the case view: a service worker with an offline progress-sync queue, cached user state for offline reads, and offline / update-available banners
  • Canvas LTI: Implemented Canvas LTI launch with user provisioning, learner enrollment, and single sign-on into the platform
  • Accessibility & Testing: Delivered WCAG 2.1 AA improvements (semantic HTML, ARIA) and added Playwright with Guidepup automated screen-reader end-to-end tests; stabilized the suite and SendGrid email delivery

Ruby on Rails Developer

Furbol (Part-time)

Jul 2024 - May 2025
  • Backend Development: Developed and maintained a Rails API supporting a Flutter mobile application following Trailblazer gem and design
  • Performance Optimization: Reduced AWS infrastructure costs by 60% through service reviews, query optimization, memoization, and API performance tuning
  • Reliability & Monitoring: Implemented Sentry for real-time error tracking and faster incident resolution
  • Notifications: Upgraded Firebase Cloud Messaging to HTTP v1, ensuring stable and reliable push notifications
  • Testing & Quality: Increased Rails API test coverage from 71% to 97% using RSpec
  • Feature Development: Implemented user blocking logic, booking system improvements, cron jobs, analytics integration, and rich snippets
  • Data & Localization: Optimized PostgreSQL queries, serializers, and implemented locale/translations improvements
  • Team Collaboration: Participated in sprint planning, backlog refinement, and collaborated with Flutter developers
  • Tooling: Adopted GitLab for version control and CI workflows

Ruby on Rails Developer on Testing & Automation

Medical American Company (Contract)

Feb 2024 - Jun 2024
  • Feature Cleanup: Removed legacy feature flags after the adoption of a new Rails engine
  • Testing: Wrote RSpec and Capybara unit and integration tests, ensuring full test coverage
  • Codebase Modernization: Improved maintainability and reduced technical debt
  • Open Source Contribution: Co-authored Rails framework enhancement that deprecated Sprockets as the default asset pipeline, affecting all new Rails applications

Ruby on Rails Developer

United Nations | UNFICYP (Volunteer)

Feb 2023 - Feb 2024
  • Full-Stack Development: Independently designed, developed, and deployed a Ruby on Rails application to streamline military operations
  • End-to-End Ownership: Managed requirements gathering, development, testing, and deployment
  • Deployment: Deployed and maintained the application on Render
  • Data Handling: Built structured data workflows to improve operational reporting and decision-making
  • Impact: Enhanced operational visibility for field teams

Ruby on Rails Developer

The Odin Project (Project-Based Training)

Dec 2021 - Oct 2024
  • Built a full-featured Rails application replicating core Facebook backend functionalities
  • Implemented authentication, associations, validations, and RESTful APIs
  • Applied MVC best practices, object-oriented design, and Git-based workflows

Education

Programming and Web Development

Self-taught & The Odin Project

2020 - 2026

Logic, Algorithms, Data Structures, Python, Ruby, Ruby on Rails, JavaScript, Object-Oriented Programming, SOLID design, REST, and modern web technologies

View Projects →

Logistics

Aeronautical University, Argentina

2019 - 2020

Pedagogy

Interamerican Open University, Argentina

2017 - 2018

Aircraft Systems

Aeronautical University, Argentina

2011 - 2014

The Blog

OffTheRails

Field notes from a Ruby on Rails developer who writes down every correction twice so he doesn't make it three times.

Rails PostgreSQL evil_seed Anonymization

How I load anonymized production data into dev with evil_seed

Every developer on the team gave up half their disk to a production database dump full of PII, and the download took hours. I refused, lived on seeds, and one day was asked to ship a comprehensive anonymized demo DB. A top-down evil_seed walk would not stop pruning. Bottom-up worked, and the dump dropped to a fraction of the original.

Federico Sapuppo · · ~7 min read
Read post
macOS AI Data Loss Backups

How two AIs made me wipe my Mac

I needed disk space to restore a production database. I asked Claude for the biggest folders, got a sudo rm -rf for 48 GB of iOS simulators, and checked it against Gemini first. Both said it was safe. It deleted my entire home folder, the Time Machine snapshot, and recovery mode along with it. Here is what actually got me back.

Federico Sapuppo · · ~6 min read
Read post
Hermes AI Agents Telegram Skills

Sergio rides shotgun

My phone buzzed at 9:30 AM with a tax-return reminder. I sent back two words and a few minutes later the transaction came back filed. Same week, a voice memo from a toll booth turned into a labor settlement package citing Article 232. This is what happens when you put an open-source agent on Fly.io and talk to it through Telegram.

Federico Sapuppo · · ~5 min read
Read post
También en español
Rails Notifications AI Workflow

From 3 AM deploys to a notifications skill: shipping web push with Noticed and AI help

The last time I shipped push notifications, I did it from my bed at 3 AM. A few years later, on a different app, I had to do it again. This time, at scale: 25 legacy mailers, a feature flag, an AI workflow, and one nasty bug where push subscriptions leaked between users on the same laptop.

Federico Sapuppo · · ~8 min read
Read post
Omarchy Arch Linux T2 Mac Kernel

If your MacBook falls off a desk, install Omarchy

My M3 Pro's screen cracked, my backup was a 2018 Intel MacBook Air that macOS had given up on, so I installed DHH's Arch distro on it. One discussion comment later, I was sending pull requests to basecamp/omarchy. Most merged within hours, and two days later they shipped inside Omarchy 3.5, plus a three-line kernel patch for the T2 SMC.

Federico Sapuppo · · ~7 min read
Read post

Get in Touch

I'm currently available for freelance work and open to new opportunities. Fluent in English, native Spanish speaker, with knowledge of German.

Software, agents & AI automation fedesapuppo@railspilot.ai
Bookkeeping fedesapuppo@crossledger.net
Other enquiries fedesapuppo@hotmail.com
(+54) 9 3547468121
linkedin.com/in/federicosapuppo
github.com/fedesapuppo