# Built a native macOS messaging client in Swift 6 and SwiftUI — 11,141 lines across 53 files — over the C interface of a Rust core linked as a static archive from a pinned revision. 2025 **Situation.** The messaging protocol had a well‑tested core written in Rust and clients on several platforms, but the desktop experience on macOS was a cross‑platform shell — it did not look like a Mac application, did not behave like one, and carried a runtime that a native application does not need. The core exposes its capability through a C interface, which means any language that can call C can build on it, and Swift can. **Task.** A native client had to be built directly on that C interface, in the platform's current language and current interface framework, with the core linked in rather than shipped alongside. **Action.** The application is 11,141 lines of Swift across fifty‑three files in the app target, built on SwiftUI with the core linked as a static archive compiled from a pinned upstream revision. Pinning the revision rather than tracking a branch is the decision that makes the build reproducible: the C interface is the contract, and a moving core changes the contract without changing a line of Swift. The layering keeps the unsafe surface small — a thin wrapper owns every pointer and every string that crosses the boundary, models above it are ordinary Swift values, and the interface layer never sees a raw pointer. Everything the C interface returns has an ownership rule, and getting one wrong produces either a leak or a crash with no compiler warning in between, so the wrapper is where the entire project's memory discipline lives. The build is driven by a task runner with fifty‑six targets covering the core compile, the Swift build, the test suites, the linters and the packaging. **Result.** A native client that starts as a Mac application, uses the platform's own materials and controls, and carries no embedded browser. What has not been done should be stated: this is not a shipped release. There is no notarised distribution, no update channel, and one language in the interface, so it is a working application rather than a product anyone else is running. --- - Role: macOS Application Engineer - Categories: [Solution Architecture](https://engineer.company/categories/solution-architecture/), [Frontend Engineering](https://engineer.company/categories/frontend/), [Full‑Stack Development](https://engineer.company/categories/full-stack/), [APIs & Integration](https://engineer.company/categories/api/), [Design Systems & UI](https://engineer.company/categories/design-systems/), [UX / UI Design](https://engineer.company/categories/ux-ui/) - Services: [Platform & Solution Architecture](https://engineer.company/services/platform-architecture/), [Frontend Development](https://engineer.company/services/frontend-development/), [Full‑Stack Product Development](https://engineer.company/services/full-stack-development/), [UI/UX Design & Design Systems](https://engineer.company/services/ui-ux-design/)