Senior .NET Modernization Engineer — Legacy System Rewrite (Long-Term)

We're supporting a US industrial manufacturer through the modernization of a business-critical production system originally built in 2008. The application manages materials operations across a plant — inventory tracking, load scheduling and dispatch, scale and device interfaces, and an optimization model that selects the lowest-cost material mix for production. It has been maintained incrementally for well over a decade, but the underlying architecture has never changed, and it's now time for a proper rewrite. The current estate is .NET Framework 4.8, WinForms deployed via ClickOnce to local machines, tablets, and terminal servers, backed by SQL Server 2022. There are around seven separate applications alongside standalone Windows services that read from plant-level devices and write to the database, plus WCF services and integrations to scheduling, a process data warehouse, and downstream accounting systems. The target is .NET 10 LTS with a modular architecture: dependency injection throughout, real unit test coverage, clean interfaces between components, and connectors isolated so a single integration can be updated and redeployed without rebuilding everything. Alongside the code, we're redesigning the data structures for consistency, proper uniqueness constraints, and a real audit trail, with a migration path that carries existing history into the new schema. We're looking for a senior engineer who has done this kind of legacy modernization before on a system people depend on daily — someone who can help scope and sequence the work into deliverable phases, then build. The engagement starts with a discovery phase working through the end-to-end process with operations, process control, and accounting stakeholders before any code is written. Depending on how the plan shapes up, this may grow into a small team, so experience leading or coordinating other developers is valuable. What we're looking for: Deep .NET experience across Framework and modern .NET, with a track record of migrating legacy applications rather than greenfield builds Strong SQL Server, including schema redesign and data migration Practical experience with dependency injection, unit testing, and modular architecture in a brownfield codebase Comfortable working directly with non-technical operations stakeholders, not just other developers Based in the United States preferred, for timezone overlap and close collaboration with the client team Nice to have: manufacturing or heavy industrial experience; WinForms and WCF familiarity; exposure to plant-floor systems, device servers, or HMI; experience with optimization or linear programming models. In your proposal, please include a short description of a legacy system you personally modernized — what it was, what the target architecture was, and how you sequenced the work.