feat(frontend,wire): surface system (FE slice 1) + @dispatch/wire types-only split (B2)

FE slice 1 — backend-declared, frontend-agnostic surface system (verified live): new types-only @dispatch/ui-contract (SurfaceSpec / field kinds / region / ActionRef / catalog), surface-registry (typed service handle), transport-ws (Bun WS :24205, path-agnostic upgrade), surface-loaded-extensions (first real surface); kernel HostAPI.getExtensions; host-bin wiring; bin/up. Harness: retire AGENTS 'backend only', ORCHESTRATOR §3/§7/§8, frontend-design.md locked.

B2 — wire-types split (chat-slice prerequisite): new types-only @dispatch/wire single-sources the wire ABI (AgentEvent + 11 variants; conversation model Chunk/ChatMessage/Role/TurnId/StepId + 6 chunk variants; Usage) with zero @dispatch/* deps. @dispatch/kernel re-exports via shims so its public surface is byte-identical (zero consumer blast radius). transport-contract re-exports AgentEvent from @dispatch/wire and drops its @dispatch/kernel dependency, so HTTP clients (the web frontend) consume the wire without the kernel runtime.

tsc -b + biome clean; 460 vitest + 77 bun pass.

6 files changed, 187 insertions, 0 deletions

diff --git a/packages/surface-loaded-extensions/package.json b/packages/surface-loaded-extensions/package.json
new file mode 100644
index 0000000..66e2e69
--- /dev/null
+++ b/packages/surface-loaded-extensions/package.json
@@ -0,0 +1,13 @@
+{
+	"name": "@dispatch/surface-loaded-extensions",
+	"version": "0.0.0",
+	"type": "module",
+	"private": true,
+	"main": "dist/index.js",
+	"types": "dist/index.d.ts",
+	"dependencies": {
+		"@dispatch/kernel": "workspace:*",
+		"@dispatch/ui-contract": "workspace:*",
+		"@dispatch/surface-registry": "workspace:*"
+	}
+}
diff --git a/packages/surface-loaded-extensions/src/extension.ts b/packages/surface-loaded-extensions/src/extension.ts
new file mode 100644
index 0000000..abef4b6
--- /dev/null
+++ b/packages/surface-loaded-extensions/src/extension.ts
@@ -0,0 +1,43 @@
+import type { Extension, HostAPI, Manifest } from "@dispatch/kernel";
+import type { SurfaceProvider } from "@dispatch/surface-registry";
+import { surfaceRegistryHandle } from "@dispatch/surface-registry";
+import { buildLoadedExtensionsSpec } from "./spec.js";
+
+export const manifest: Manifest = {
+	id: "surface-loaded-extensions",
+	name: "Loaded Extensions Surface",
+	version: "0.0.0",
+	apiVersion: "^0.1.0",
+	trust: "bundled",
+	activation: "eager",
+	dependsOn: ["surface-registry"],
+	contributes: { services: [] },
+};
+
+export function createLoadedExtensionsExtension(): Extension {
+	let dispose: (() => void) | undefined;
+
+	return {
+		manifest,
+		activate(host: HostAPI) {
+			const registry = host.getService(surfaceRegistryHandle);
+
+			const provider: SurfaceProvider = {
+				catalogEntry: {
+					id: "loaded-extensions",
+					region: "side",
+					title: "Loaded Extensions",
+				},
+				getSpec() {
+					return buildLoadedExtensionsSpec(host.getExtensions());
+				},
+				invoke() {},
+			};
+
+			dispose = registry.register(provider);
+		},
+		deactivate() {
+			dispose?.();
+		},
+	};
+}
diff --git a/packages/surface-loaded-extensions/src/index.ts b/packages/surface-loaded-extensions/src/index.ts
new file mode 100644
index 0000000..bc10dc5
--- /dev/null
+++ b/packages/surface-loaded-extensions/src/index.ts
@@ -0,0 +1,2 @@
+export { createLoadedExtensionsExtension, manifest } from "./extension.js";
+export { buildLoadedExtensionsSpec } from "./spec.js";
diff --git a/packages/surface-loaded-extensions/src/spec.test.ts b/packages/surface-loaded-extensions/src/spec.test.ts
new file mode 100644
index 0000000..9c1aa6a
--- /dev/null
+++ b/packages/surface-loaded-extensions/src/spec.test.ts
@@ -0,0 +1,94 @@
+import type { Manifest } from "@dispatch/kernel";
+import type { StatField } from "@dispatch/ui-contract";
+import { describe, expect, it } from "vitest";
+import { buildLoadedExtensionsSpec } from "./spec.js";
+
+function fakeManifest(id: string, name: string, version: string): Manifest {
+	return {
+		id,
+		name,
+		version,
+		apiVersion: "^0.1.0",
+		trust: "bundled",
+	};
+}
+
+describe("buildLoadedExtensionsSpec", () => {
+	it("returns a count stat of '0' and no extension stats for empty manifests", () => {
+		const spec = buildLoadedExtensionsSpec([]);
+
+		expect(spec.id).toBe("loaded-extensions");
+		expect(spec.region).toBe("side");
+		expect(spec.title).toBe("Loaded Extensions");
+		expect(spec.fields).toHaveLength(1);
+		expect(spec.fields[0]).toEqual({
+			kind: "stat",
+			label: "Loaded",
+			value: "0",
+		});
+	});
+
+	it("returns a count stat plus one stat per manifest in order", () => {
+		const manifests = [
+			fakeManifest("alpha", "Alpha", "1.0.0"),
+			fakeManifest("beta", "Beta", "2.3.1"),
+			fakeManifest("gamma", "Gamma", "0.5.0"),
+		];
+
+		const spec = buildLoadedExtensionsSpec(manifests);
+
+		expect(spec.fields).toHaveLength(4);
+		expect(spec.fields[0]).toEqual({
+			kind: "stat",
+			label: "Loaded",
+			value: "3",
+		});
+		expect(spec.fields[1]).toEqual({
+			kind: "stat",
+			label: "Alpha",
+			value: "1.0.0",
+		});
+		expect(spec.fields[2]).toEqual({
+			kind: "stat",
+			label: "Beta",
+			value: "2.3.1",
+		});
+		expect(spec.fields[3]).toEqual({
+			kind: "stat",
+			label: "Gamma",
+			value: "0.5.0",
+		});
+	});
+
+	it("preserves input order of manifests", () => {
+		const manifests = [
+			fakeManifest("z-last", "Z Last", "1.0.0"),
+			fakeManifest("a-first", "A First", "2.0.0"),
+		];
+
+		const spec = buildLoadedExtensionsSpec(manifests);
+
+		expect((spec.fields[1] as StatField).label).toBe("Z Last");
+		expect((spec.fields[2] as StatField).label).toBe("A First");
+	});
+
+	it("sets the surface id, region, and title correctly", () => {
+		const spec = buildLoadedExtensionsSpec([]);
+
+		expect(spec.id).toBe("loaded-extensions");
+		expect(spec.region).toBe("side");
+		expect(spec.title).toBe("Loaded Extensions");
+	});
+
+	it("uses manifest.name as label and manifest.version as value", () => {
+		const manifests = [fakeManifest("my-ext", "My Extension", "3.2.1")];
+
+		const spec = buildLoadedExtensionsSpec(manifests);
+
+		expect(spec.fields[1]).toEqual({
+			kind: "stat",
+			label: "My Extension",
+			value: "3.2.1",
+		});
+	});
+});
diff --git a/packages/surface-loaded-extensions/src/spec.ts b/packages/surface-loaded-extensions/src/spec.ts
new file mode 100644
index 0000000..bd3dd56
--- /dev/null
+++ b/packages/surface-loaded-extensions/src/spec.ts
@@ -0,0 +1,25 @@
+import type { Manifest } from "@dispatch/kernel";
+import type { StatField, SurfaceSpec } from "@dispatch/ui-contract";
+
+/**
+ * Pure core — builds the SurfaceSpec for the loaded-extensions surface.
+ * Zero I/O, zero ambient state. Decision logic only: input → output.
+ */
+export function buildLoadedExtensionsSpec(manifests: readonly Manifest[]): SurfaceSpec {
+	const fields: StatField[] = [{ kind: "stat", label: "Loaded", value: String(manifests.length) }];
+
+	for (const manifest of manifests) {
+		fields.push({
+			kind: "stat",
+			label: manifest.name,
+			value: manifest.version,
+		});
+	}
+
+	return {
+		id: "loaded-extensions",
+		region: "side",
+		title: "Loaded Extensions",
+		fields,
+	};
+}
diff --git a/packages/surface-loaded-extensions/tsconfig.json b/packages/surface-loaded-extensions/tsconfig.json
new file mode 100644
index 0000000..db257d0
--- /dev/null
+++ b/packages/surface-loaded-extensions/tsconfig.json
@@ -0,0 +1,10 @@
+{
+	"extends": "../../tsconfig.base.json",
+	"compilerOptions": { "rootDir": "src", "outDir": "dist", "composite": true },
+	"include": ["src/**/*.ts"],
+	"references": [
+		{ "path": "../kernel" },
+		{ "path": "../ui-contract" },
+		{ "path": "../surface-registry" }
+	]
+}