Senior React Platform Engineer

Mattermost is the leading collaborative workflow platform for defense, intelligence, security, and critical infrastructure. Trusted by the U.S. Department of War and Fortune 500s, our platform runs on\-premises and in private clouds, delivering secure messaging, file sharing, workflow automation, audio/screenshare, and project management—all with full data and operational control. Mattermost powers high\-stakes workflows across mission planning, real\-time, real\-world operations, DevSecOps, incident response, and cyber defense—enabling secure collaboration from tactical edge and DDIL environments to enterprise HQ. Teams operate across web, desktop, and mobile, with embedded interoperability for Microsoft Teams, Outlook, and Microsoft 365\. To learn more, visit www.mattermost.com Mattermost is looking for a Senior React Platform Engineer to help us redefine the limits of web application performance and reliability. You will join the Core Web team to lead the evolution of our web architecture, shared libraries, and networking strategies. Your work sits at the intersection of modern frontend infrastructure and extreme environment resilience. You'll be responsible for ensuring that our web platform is both a joy for developers to build on and a reliable tool for users in the most challenging network conditions—specifically DDIL (Disconnected, Denied, Disrupted, Intermittent, and Limited) environments. This isn't just about building features; it's about building the engine that powers them. Do you have a passion for designing and developing high\-impact products? Do you want to work with a well\-oiled, collaborative, and highly senior team? Do you want to make an impact on open source? Help us build and grow one of the largest React and Go open\-source projects. Responsibilities Include: * Implement secure communication features and real\-time messaging capabilities optimized for high\-latency or disrupted network conditions * Optimize web application performance, including bundle size, initial load time, runtime memory usage, and asset delivery pipelines * Design and maintain shared React component libraries and architectural patterns to ensure platform\-wide consistency and scalability * Collaborate with backend engineers to integrate web apps with APIs and ensure smooth data synchronization under constrained or intermittent network environments * Contribute to Mattermost's open\-source React codebase, sharing platform\-level and resilience\-focused solutions with the broader developer community * Work with product managers and designers to translate user requirements into technical solutions and prototypes, with a focus on graceful degradation and resilience * Implement comprehensive testing strategies including unit tests and automated end\-to\-end testing (e.g., Cypress or Playwright) under simulated network stress * Debug and resolve web\-specific issues across different browsers, platforms, and operating system versions. * P