Windows Extension Developer (Contractor)

About us:

Working at Tech Holding isn't just a job, it's an opportunity to be a part of something bigger. We are a full-service consulting firm that was founded on the premise of delivering predictable outcomes and high-quality solutions to our clients.  Our founders and team members have industry experience and have held senior positions in a wide variety of companies – from emerging startups to large Fortune 50 firms – and we have taken our combined experiences and developed a unique approach that is supported by the principles of deep expertise, integrity, transparency, and dependability.

The Role

We are looking for a senior Windows systems engineer to build and maintain a production-grade Windows sync client using Microsoft's Cloud Files API (CF API). You will own the low-level plumbing that makes seamless, on-demand file synchronization feel invisible to end users, from placeholder hydration and shell overlay icons to Explorer context menus and high-throughput I/O. This is a deeply technical IC role. You will work closest to the metal of the Windows platform, collaborating with product and backend teams to ship a sync client that rivals OneDrive and Dropbox in quality and reliability.

Key Responsabilities:

• Design and implement a Windows Cloud Files API (CF API) sync provider, including placeholder management, hydration/dehydration callbacks, and range-based partial hydration.
• Build robust Windows Shell integration: overlay icons, right-click context menus, and deep Windows Explorer integration via COM.
• Own Win32 and NTFS-level file system interactions, including extended attributes, reparse points, and oplocks.
• Implement high-performance I/O using IOCP and Windows thread pool APIs to handle concurrent file transfers reliably.
• Write and maintain COM servers and in-process shell extensions that meet Microsoft's strict reliability and compatibility requirements.
• Debug complex race conditions, kernel-mode interactions, and edge cases introduced by antivirus software, Group Policy, and diverse hardware configurations.
• Maintain backward compatibility across Windows 10 and Windows 11, including various enterprise and consumer SKUs.
• Instrument code with ETW tracing, WPR/WPA profiling, and crash dump analysis to diagnose production issues.
• Collaborate with QA to develop stress tests, fuzz tests, and automated regression suites for the sync engine.
• Contribute to architecture and design reviews, set engineering standards for the Windows client codebase

Required Skills:

• 5+ years of Windows systems programming in C++, with deep mastery of Win32 APIs, NTFS internals, and COM.
• Strong, hands-on experience with the Windows Cloud Files API (cfapi.h): placeholder files, CF_CALLBACK_TYPE hydration callbacks, pin/unpin semantics, and range-based partial hydration.
• Demonstrated expertise in Windows Shell integration: overlay icon handlers, context menu shell extensions, and Explorer namespace extensions via COM.
• Solid multithreading experience using IOCP, Windows thread pools, and synchronization primitives (events, mutexes, critical sections, slim reader/writer locks).
• Has shipped at least one production Windows sync client (cloud storage client, backup agent, or equivalent),  this is non-negotiable.

Nice-to-have Skills:

• Experience with Windows kernel-mode development (filter drivers, minifilters) or deep knowledge of the Windows I/O stack.
• Familiarity with Windows Security: ACLs, privilege management, integrity levels, and UAC.
• Prior work on enterprise software distributed via MSI/MSIX with silent install and Group Policy support.
• Experience contributing to or maintaining large-scale C++ codebases with CI/CD pipelines (GitHub Actions, Azure DevOps).
• Familiarity with WinRT APIs and bridging classic Win32 components to modern Windows Runtime environments.
• Background in network programming (HTTP/2, WebSockets, chunked transfer) in the context of cloud sync.

What we offer:

• Fully remote engagement across MX.
• Opportunity to work on high-impact client systems with real operational ownership.

Employment type:

• Contract

Tech Holding is proud to be an Equal Opportunity Employer and is committed to fostering a diverse and inclusive workplace. We welcome applicants from all backgrounds and experiences, and we consider qualified applicants without regard to race, color, religion, gender, sexual orientation, gender identity, national origin, disability, veteran status, or any other legally protected characteristic. If you require accommodation in the application process, please contact our HR