Reliable Senior Developer Needed - On-Call Maintenance Retainer (Web App)

Looking for a dependable senior developer for an ongoing maintenance retainer (not full-time): when something breaks on our custom-built photo editor app, we need someone we can reach who fixes it fast and who can also implement improvements as we request them over time. Right now our editor runs on a third-party SaaS: costly, and we have zero control over it no way to adapt it to our needs. So we're building our own in-house editor to get off it. The developer building it is handling initial development only he won't be taking on maintenance afterward. We're looking for a senior developer to take over ongoing maintenance and continuous improvement of this editor, on a maintenance retainer (not full-time volume varies based on needs). Stack: Bun backend, React frontend (fully responsive, mobile-heavy traffic), Shopify (theme dev, Storefront/Admin API). What you'll do: - Pick up a codebase you didn't write and get up to speed fast - Respond quickly when something's reported (bug, blocker, outage) same-day fixes - Solve problems autonomously, without technical supervision - Implement requested features/improvements over time - Manage and maintain the connections with our Shopify back office You're a fit if you have: Senior-level experience with production web apps Proven experience with e-commerce/Shopify integrations A track record of taking over and maintaining legacy/existing code A reputation for being responsive, reliable, and autonomous Solid written English (we work async, in writing) Contract type: Ongoing maintenance retainer not full-time. You're called on when something breaks or an evolution is requested.