Kakehashi: run macOS ARM64 binaries on Linux aarch64, no JIT

Kakehashi is an experimental userspace translation layer that loads Darwin Mach-O binaries and executes them natively on Linux aarch64, without a JIT. It maps a freestanding libSystem and translates BSD syscalls to their Linux equivalents, letting real macOS CLI tools — 7-Zip's 7zz, curl, threaded programs — run unmodified. It's been verified on Docker/Colima and UTM.

The project's core pitch isn't raw speed but CI economics: on GitHub Actions, macOS runners cost roughly 10-12x more per minute than Linux arm64 runners. Even though Darwin binaries under Kakehashi run about 5x slower on multi-file, syscall-heavy workloads (the gap shrinks to ~1.1-1.2x for compression-heavy, few-file cases), the total billable cost can still come out lower than paying for macOS capacity outright.

Kakehashi is explicitly not a full macOS emulator yet — no GUI, codesign/notarization, complete Apple Security.framework, or full curl feature parity. It positions itself as a CLI-focused CI tool rather than a product claim. Written in Rust, installable via cargo install kakehashi, requiring Rust 1.88+ and a Linux aarch64 host to execute guest binaries.