Introduction

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The model

• Commands — a request/response call from the driver to Drawdy. You ask Drawdy to do something (add elements, move the camera, read the selection) and await the result.
• Subscriptions — a long-lived registration. You issue a subscription command once; Drawdy then pushes events to your driver whenever the thing you subscribed to happens.

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Two guarantees

1. Every request has a response. Unlike LSP notifications, every command you issue resolves — with a value or an error — so the driver always knows whether Drawdy processed it. See LSP could have been better for the reasoning.
2. Requests are processed in order. Commands sent to Drawdy are handled in the order they are received.

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What a driver looks like

import type { DriverModule } from "@drawdy/driver-protocol";

export const activate: DriverModule["activate"] = async (ctx) => {
    // register menus, panels, subscriptions; issue commands via ctx.issueCommand
};

export const onEvent: DriverModule["onEvent"] = async (event) => {
    // react to subscription events
};