This package is the macOS analogue of xbox/runtime: an AC BIOS contract for a native host with an embedded JavaScript interpreter. It does not require a WKWebView, DOM, Safari, or Web Audio. A production host binds these protocols to Metal, Core Audio (or a carefully preallocated AVAudioEngine graph), GameController/AppKit, URLSession, and sandboxed storage.

AC piece surface	Swift	Xbox/C++
`boot/sim/paint/act/leave`	`ACPiece`	`ac::xbox::Piece`
runtime context	`ACApi`	`ac::xbox::Api`
2D draw commands	`ACGraphics`	`Graphics`
models/textures/shaders	`ACRenderer` (Metal handles)	future D3D renderer
immediate synth/sample	`ACSound` (Core Audio)	`Sound` (XAudio2)
normalized input	`ACInputMap`	`input_map.hpp`
downloaded source metadata	`ACPieceBundle`	`PieceBundle`
embedded JS seam	`ACJSEngine`	`JsEngine`
atomic live reload	`ACPieceSupervisor` actor	`PieceSupervisor`

The remote endpoint supplies UTF-8 source with an immutable version and SHA-256. The supervisor enforces a source bound, verifies the digest, compiles and boots in a fresh interpreter, then activates only at the host's frame boundary. The old interpreter is retained during a bounded callback probation window. Throws or watchdog overruns trigger rollback without restarting the native process.

The JavaScript adapter should expose only AC bindings. Do not expose Process, the filesystem, Objective-C reflection, raw sockets, browser globals, or dynamic native loading. Remote content is piece data; native BIOS changes remain signed application updates.

Run the contract tests with:

cd macos/runtime
swift test

macos/fight-runner remains the WebKit comparison harness. This package is the foundation for the direct native runner: add concrete Metal/Core Audio adapters and a pinned embedded interpreter, then run the same fight bundle used by the Xbox BIOS.