macOS Extension Developer (Contractor)

The Role

We are looking for a senior macOS systems engineer with deep expertise in file system extensions and kernel-adjacent frameworks. You will be responsible for building and maintaining a production-grade sync or virtual drive client on macOS, one that users depend on every day. This is a technically demanding role suited to an engineer who has shipped real software in this space and understands the nuances of Apple's extension model from entitlements to on-demand resource management.

Key Responsibilities:

• Design, implement, and maintain macOS File Provider extensions using NSFileProviderExtension and related APIs
  • Item enumeration, working set management, and placeholder lifecycle
  • On-demand downloading and eviction of file content
  • Conflict detection and resolution strategies
• Integrate and maintain macFUSE-based virtual file systems
  • Implement low-level FUSE operations: read, write, getattr, readdir, open, release
  • Handle partial byte-range reads for large file streaming scenarios
• Manage macOS System Extension lifecycle including code signing, notarization, entitlements, and sandboxing requirements
• Build and maintain XPC services for secure inter-process communication between the extension and host app
• Write idiomatic Swift using modern concurrency patterns (async/await, actors, structured concurrency)
• Diagnose and resolve complex, hard-to-reproduce issues at the intersection of the kernel, file system, and user space
• Collaborate with product and backend teams to define sync protocols and surface reliable UX

Required Skills:

• 5+ years of macOS development experience, with a focus on system-level or framework-level work
• Strong hands-on experience with the FileProvider framework
  • NSFileProviderExtension, NSFileProviderItem, and domain management
  • Item enumeration, on-demand download, and working set eviction
  •  Conflict resolution and syncing state machines
• Practical experience with macFUSE
  • Implementing core FUSE operations: read, write, getattr, open, readdir
  • Handling partial byte-range reads
  • Debugging kernel panics and FUSE-layer failures
• Deep understanding of macOS System Extensions
  • Code signing and notarization workflows
  • Entitlement management and capability provisioning
  • Sandbox constraints and their impact on file system access
• Proficiency with Swift async/await and XPC services for IPC
• Has shipped a production macOS sync client, cloud drive, backup tool, or similar, that real users depend on

Nice-to-have Skills:

• Experience with network file system protocols (WebDAV, SMB, NFS) at the application layer
• Familiarity with FSEvents for file system monitoring
• Prior experience with Endpoint Security or Network Extension frameworks
• Contributions to open-source macOS tooling or FUSE projects
• Background in cloud storage, backup, or enterprise file management products
• Familiarity with TestFlight distribution and enterprise MDM deployment of system extensions

What we offer:

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

Employment type:

• Contract