Senior Full-Stack Developer (.NET + React/Vite + Capacitor) — Ongoing SaaS Platform

We're looking for a senior full-stack developer to take ownership of the technical side of a B2B SaaS platform serving fitness and nutrition professionals in Brazil. The platform is live, functional, and being actively used by paying customers — this is not a greenfield project. About the situation: I'm the founder and run commercial operations (product, marketing, sales). My previous technical co-founder has exited the company, and I've been managing day-to-day technical operations with AI-assisted tools since then. I'm now looking for an experienced developer who can work independently, make sound architectural decisions, and take real ownership — not someone who needs close technical supervision, since I don't have an internal technical team. Tech stack: - Backend: C# / .NET - Frontend (web): React + Vite - Mobile: Capacitor (iOS + Android, wrapping the web app) - REST API architecture Scope of work: - Review and get familiar with the existing codebase and architecture - Ongoing feature development based on product roadmap - Bug fixes and maintenance - Technical guidance on scaling decisions (we're pre-launch, growing towards full public launch with iOS/Android app store submissions in progress) - Eventually: help evaluate and potentially mentor/hire additional developers as the team grows What I'm looking for: - 5+ years of experience with C#/.NET and React - Experience with mobile hybrid frameworks (Capacitor, Ionic, or similar) - Comfortable working autonomously and communicating clearly with a non-technical founder — you'll need to explain technical trade-offs in plain language - Experience owning a codebase end-to-end, not just executing tickets - Strong async communication skills (we're not always in the same timezone) How we'll start: To make sure it's a good fit on both sides, we'll start with a paid trial engagement (~5-10 hours) focused on a technical audit of the existing codebase and a small scoped task. Based on that, we'll move to an ongoing weekly arrangement. Please do not apply if you're early-career or require close technical supervision — this role requires someone who can work independently. Language requirement: Fluent Portuguese is required for this role (written and spoken). Most of our day-to-day communication — calls, technical discussions, and documentation — happens in Portuguese, so this is a hard requirement, not a preference.