msd-core/docs/tutorials/embed-gsd-in-a-new-host.md

Tutorial: embed GSD in a new host

This tutorial walks through embedding GSD's orchestration loop into a brand-new host end-to-end — from classifying the host, to composing the engine adapters, to running a GSD command through the embedded engine. It is the learning path that pairs with the how-to (steps) and the reference (spec).

You will build a minimal programmatic-cli host-plugin that invokes a GSD command via the embedded engine. No gsd-core source changes.

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Prerequisites

• The GSD Host-Integration SDK entry importable in your host's runtime.
• Your host's authoritative docs open (you'll declare axes from them, never infer).

Step 1 — Classify the host

Your host is a programmatic CLI with an event bus and a passive model (it can only receive prompts, not call a model for you). That is the programmatic-cli profile.

const SDK = require('@opengsd/gsd-core/sdk');
// Confirm the profile from your declared axes:
const profile = SDK.profileOf({ embeddingMode: 'imperative', runtime: 'node' });
// → 'programmatic-cli'

Step 2 — Compose the engine adapters

const hookBus = SDK.createHookBus({ bus: 'host' });     // your host fires events
const model   = SDK.createModelAdapter({ modelMode: 'passive' });
const stateIO = SDK.createStateIO({ io: 'filesystem' });
const adapter = SDK.createImperativeAdapter({ runtime: 'my-cli' });

Step 3 — Negotiate capabilities

const req = SDK.buildHandshakeRequest({
  embeddingMode: 'imperative', commandSurface: 'slash-file', modelMode: 'passive',
  hookBus: 'host', stateIO: 'filesystem', transport: 'mcp', runtime: 'node',
});
const { effective, points, warnings } = SDK.handleHandshakeRequest(req);
// `effective` is the negotiated capability set; `points` is per-interface-point
// degradation; `warnings` flags any axis the host omitted.

Step 4 — Run a GSD command through the embedded engine

The imperative adapter exposes the engine surface; your host binds its command surface (slash commands, palette, chat) to it. A user invoking /gsd:phase in your host dispatches through the embedded engine exactly as it would in a first-party host — that is the parity the interface guarantees.

Step 5 — Verify parity

Assert that your host-plugin, built from the SDK entry alone, produces the same negotiated result as the in-process path. The SDK smoke test (tests/sdk-smoke.test.cjs) is the template — copy its structure for your host's own parity test.

Recap

You classified a host, declared its axes from authoritative docs, composed the adapters, negotiated capabilities over the (serialized) handshake, and ran a GSD command through the embedded engine — all without touching gsd-core source. A new host is now a plugin you wrote.

Next

• How-to: author a host-plugin — the step-by-step reference.
• Interface versioning policy — how the surface evolves.