feat(#1683): published Host-Integration SDK surface + smoke test — Slice 2 (#1939)

The SDK entry (src/host-integration-sdk.cts) is the single PUBLIC surface a
host-plugin author imports: the negotiated schema + classification, the five
adapters (declarative/imperative/model/hook/state), and the serialized
handshake. Frozen so the public shape cannot be mutated. Everything else in
gsd-core stays internal.

tests/sdk-smoke.test.cjs imports ONLY from the SDK entry and builds a
third-party host-plugin end-to-end (compose adapters + handshake + classify) —
proving an external author can wire a host without gsd-core internals (#1683 AC).
ESLint-ignore + inventory manifest kept in sync for the new tsc-emitted module.

src/host-integration-sdk.cts

@@ -0,0 +1,58 @@
+/**
+ * Host-Integration SDK — the published public surface (ADR-1239 Phase E / #1683).
+ *
+ * External host-plugin authors import ONLY from this entry. It IS the contract:
+ * everything it re-exports is public + versioned (PROTOCOL_VERSION governs the
+ * set); everything else in gsd-core is internal. An SDK smoke test
+ * (tests/sdk-smoke.test.cjs) builds a new host-plugin against this surface only
+ * — proving an external author can wire a host without reading gsd-core internals.
+ *
+ * Surface: the negotiated schema + classification, the five adapters
+ * (declarative/imperative/model/hook/state), and the serialized handshake.
+ * Frozen so the public shape cannot be mutated by consumers.
+ */
+'use strict';
+
+// eslint-disable-next-line @typescript-eslint/no-require-imports
+import hostIntegration = require('./host-integration.cjs');
+// eslint-disable-next-line @typescript-eslint/no-require-imports
+import adapterDeclarative = require('./adapter-declarative.cjs');
+// eslint-disable-next-line @typescript-eslint/no-require-imports
+import adapterImperative = require('./adapter-imperative.cjs');
+// eslint-disable-next-line @typescript-eslint/no-require-imports
+import modelAdapter = require('./model-adapter.cjs');
+// eslint-disable-next-line @typescript-eslint/no-require-imports
+import hookBus = require('./hook-bus.cjs');
+// eslint-disable-next-line @typescript-eslint/no-require-imports
+import stateIo = require('./state-io.cjs');
+// eslint-disable-next-line @typescript-eslint/no-require-imports
+import handshake = require('./handshake-serialized.cjs');
+
+const SDK = Object.freeze({
+  // ── Schema + protocol version ────────────────────────────────────────────
+  PROTOCOL_VERSION: hostIntegration.PROTOCOL_VERSION,
+  HOST_INTEGRATION_AXES: hostIntegration.HOST_INTEGRATION_AXES,
+  INTERFACE_POINTS: hostIntegration.INTERFACE_POINTS,
+  PROFILE_BASELINES: hostIntegration.PROFILE_BASELINES,
+
+  // ── Negotiation + classification ─────────────────────────────────────────
+  negotiateHostCapabilities: hostIntegration.negotiateHostCapabilities,
+  profileOf: hostIntegration.profileOf,
+  degradationFor: hostIntegration.degradationFor,
+  hookEventSurfaceFor: hostIntegration.hookEventSurfaceFor,
+  shouldFlattenDispatch: hostIntegration.shouldFlattenDispatch,
+
+  // ── Embedding + engine adapters ──────────────────────────────────────────
+  createDeclarativeAdapter: adapterDeclarative.createDeclarativeAdapter,
+  createImperativeAdapter: adapterImperative.createImperativeAdapter,
+  createModelAdapter: modelAdapter.createModelAdapter,
+  createHookBus: hookBus.createHookBus,
+  createStateIO: stateIo.createStateIO,
+
+  // ── Serialized handshake (out-of-process SDK hosts: pi / VS Code) ─────────
+  HANDSHAKE_METHOD: handshake.HANDSHAKE_METHOD,
+  buildHandshakeRequest: handshake.buildHandshakeRequest,
+  handleHandshakeRequest: handshake.handleHandshakeRequest,
+});
+
+export = SDK;