0010: Native Apple Silicon macOS

Status: accepted for development. The published 0.1.0 platform scope remains ADR 0007: Linux x86-64 first.

Add native aarch64-apple-darwin support with macOS 15 as the minimum, verified on native hosted macOS 15 and 26 runners. Cross-compilation cannot establish runtime support, and the maintainer has no macOS hardware. Support requires the complete applicable Command contract and Numerical profile checks, plus installation and execution of the same checksummed archive on both baselines. Once delivered in a release, this platform scope supersedes ADR 0007.

Use the built-in Sort route, including Spill, on macOS. Keep Linux external supervision and its helper confined to Linux. Native OS primitives implement standard streams, signals, randomness, terminal detection and private temporary storage; software arithmetic and built-in locale rules preserve Portable results under ADR 0003: Portable results.

Build the archive once with MACOSX_DEPLOYMENT_TARGET=15.0, record source, compiler, flags and hashes, and install those bytes outside the checkout. The archive contains one executable with target-specific license notices. The installer uses macOS’s checksum tool and retains an existing installation when a download or checksum fails. CI artifacts are development evidence; publishing a release remains a separate maintainer action.

Intel macOS, macOS before 15, native Windows and macOS external supervision remain outside scope. Hosted GNU comparisons describe the tested workloads and runners, without carrying Linux benchmark claims over to macOS.