A small SDK-capable executable demonstrating how an application links its own Rust tool crates into an OpenWorker host. It is not a desktop application.

cd harness
cargo build --release --locked -p native-tools-runtime
cargo test --locked -p notification-tools -p device-tools -p computer-tools --lib

Use target/release/native-tools-runtime (.exe on Windows) as the SDK-managed child executable. For embedded Rust, register the same crates in the registry passed to Harness::builder().tools(registry).

notification-tools: notifications.notify_user emits a UI notification event. A separately invoked macOS dialog example is opt-in and not part of normal tests.
device-tools: device.computer_status, device.audio_status, device.set_volume, device.open_settings use native Windows APIs; other platforms return unsupported, not simulated results.
computer-tools: bounded Windows screenshot/input operations with explicit access grants, observation identities and expiry. See that crate's source and computer-use boundary.

Registration does not expose every tool to every agent. Select qualified tool names in each agent/coworker definition. Native callbacks carry the host process's privileges; approval and OS sandboxing are separate concerns. Do not grant access to the desktop or change device settings in unattended test runs.