WACS.WASI.Preview3 0.2.3

WACS.WASI.Preview3

WASI Preview 3 host bindings for WACS, pinned to wasi-0.3.0-rc-2026-03-15.

Sibling of WACS.WASI.Preview2. Where Preview 2 uses synchronous host imports (io/streams.output-stream.write etc.), Preview 3 uses the Component Model async ABI — host imports take stream<T> / future<T> handles and return future<...>, with the host's async work driven by the canon-async dispatcher (WACS.ComponentModel.Async.AsyncDispatcher).

v0 status

Vertical slice per the WASIp3 plan: wasi:cli/run (async entry point), wasi:cli/{stdin,stdout,stderr} (stream-based stdio), and the stream<u8> ↔ System.IO.Stream bridge.

• Package skeleton + interfaces.
• Default Console.Open{StandardInput,StandardOutput,StandardError} backings.
• Bridge code from StreamBuffer<byte> (canon-async data plane) to host Stream.
• Test harness placeholder.

Not yet wired: end-to-end binding from a wit-component- emitted .component.wasm to these interfaces. The canon-async binder + shim recognizer (WACS.ComponentModel 0.8.13+) cover the read side; the host binding layer here registers delegates that the canon-async binder will call. Validation against a real fixture awaits wasi-0.3.0-rc-2026-03-15 toolchain stabilization in bytecodealliance/wasm-tools + wit-bindgen.

How it composes

var runtime = new WasmRuntime();
var host = runtime.UseWasiPreview3(b =>
{
    b.Stdout = new ConsoleStdio(Console.Out);
});
// Once a wit-component-emitted .component.wasm is available,
// the component's wasi:cli/stdout import resolves to
// host.Stdout.WriteViaStream(...).

Layout

Mirrors WACS.WASI.Preview2:

Wacs.WASI.Preview3/
  Cli/
    CliRun.cs       — host-side hook for invoking exported run().
    CliStdio.cs     — IStdin / IStdout / IStderr interfaces +
                      Console-backed defaults.
  Io/
    StreamBridge.cs — StreamBuffer<byte> ↔ System.IO.Stream
                      adapter.
  WasiPreview3Host.cs        — composite IBindable.
  WasiPreview3HostBuilder.cs — fluent config.
  wit/deps/wasi-cli-0.3.0-rc-2026-03-15/
    package.wit

Plan reference

See docs/wasip3-phase-3-closeout.md for what the canon-async substrate underneath this package delivers, and the WASIp3 plan for the Phase 4 + Phase 5 scope.