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.

2 files changed, 118 insertions, 0 deletions

diff --git a/packages/kernel/src/host/host.test.ts b/packages/kernel/src/host/host.test.ts
index 430447c..106dd56 100644
--- a/packages/kernel/src/host/host.test.ts
+++ b/packages/kernel/src/host/host.test.ts
@@ -726,6 +726,117 @@ describe("createHost", () => {
 		});
 	});
 
+	describe("getExtensions", () => {
+		it("returns empty array when no extensions are activated", async () => {
+			const host = createHost([], deps);
+			await host.activate();
+
+			expect(host.getExtensions()).toEqual([]);
+		});
+
+		it("returns manifests of all activated extensions", async () => {
+			const a = createExtension("ext-a");
+			const b = createExtension("ext-b");
+
+			const host = createHost([a, b], deps);
+			await host.activate();
+
+			const exts = host.getExtensions();
+			expect(exts).toHaveLength(2);
+			expect(exts.map((e) => e.id)).toContain("ext-a");
+			expect(exts.map((e) => e.id)).toContain("ext-b");
+		});
+
+		it("returns manifests in activation order", async () => {
+			const a = createExtension("a");
+			const b = createExtension("b", { dependsOn: ["a"] });
+			const c = createExtension("c", { dependsOn: ["b"] });
+
+			const host = createHost([c, b, a], deps);
+			await host.activate();
+
+			const exts = host.getExtensions();
+			expect(exts.map((e) => e.id)).toEqual(["a", "b", "c"]);
+		});
+
+		it("excludes extensions that failed to activate", async () => {
+			const a = createExtension("good");
+			const b = createExtension("bad", {
+				activate: () => {
+					throw new Error("boom");
+				},
+			});
+
+			const host = createHost([a, b], deps);
+			await host.activate();
+
+			const exts = host.getExtensions();
+			expect(exts).toHaveLength(1);
+			expect(exts[0]?.id).toBe("good");
+		});
+
+		it("excludes extensions disabled by apiVersion incompatibility", async () => {
+			const good = createExtension("good");
+			const bad = createExtension("bad", { apiVersion: "^99.0.0" });
+
+			const host = createHost([good, bad], deps);
+			await host.activate();
+
+			const exts = host.getExtensions();
+			expect(exts).toHaveLength(1);
+			expect(exts[0]?.id).toBe("good");
+		});
+
+		it("returns a frozen array", async () => {
+			const ext = createExtension("ext");
+			const host = createHost([ext], deps);
+			await host.activate();
+
+			const exts = host.getExtensions();
+			expect(Object.isFrozen(exts)).toBe(true);
+		});
+
+		it("HostAPI getExtensions reflects activated extensions after full activation", async () => {
+			const a = createExtension("ext-a");
+			const b = createExtension("ext-b", {
+				dependsOn: ["ext-a"],
+				activate: () => {},
+			});
+
+			const host = createHost([a, b], deps);
+			await host.activate();
+
+			// Use getHostAPI() to verify the post-activation view
+			const api = host.getHostAPI();
+			const capturedExtsAfter = api.getExtensions();
+
+			expect(capturedExtsAfter).toHaveLength(2);
+			expect(capturedExtsAfter.map((e) => e.id)).toEqual(["ext-a", "ext-b"]);
+		});
+
+		it("HostAPI getExtensions during activation sees only previously activated", async () => {
+			const seenDuringActivation: string[][] = [];
+
+			const a = createExtension("a", {
+				activate: (host) => {
+					seenDuringActivation.push(host.getExtensions().map((e) => e.id));
+				},
+			});
+			const b = createExtension("b", {
+				activate: (host) => {
+					seenDuringActivation.push(host.getExtensions().map((e) => e.id));
+				},
+			});
+
+			const host = createHost([a, b], deps);
+			await host.activate();
+
+			// When a activates, activated[] is empty (a hasn't been pushed yet)
+			// When b activates, activated[] has [a] (b hasn't been pushed yet)
+			expect(seenDuringActivation).toEqual([[], ["a"]]);
+		});
+	});
+
 	describe("DAG errors", () => {
 		it("throws on missing dependency", () => {
 			const ext = createExtension("a", { dependsOn: ["missing"] });
diff --git a/packages/kernel/src/host/host.ts b/packages/kernel/src/host/host.ts
index 2331625..8aa4f78 100644
--- a/packages/kernel/src/host/host.ts
+++ b/packages/kernel/src/host/host.ts
@@ -57,6 +57,7 @@ export interface Host {
 	readonly getScheduledJobs: () => readonly ScheduledJob[];
 	readonly getMigrations: () => readonly string[];
 	readonly getDisabled: () => readonly DisabledExtension[];
+	readonly getExtensions: () => readonly Manifest[];
 	readonly getHostAPI: () => HostAPI;
 }
 
@@ -150,6 +151,9 @@ export function createHost(extensions: readonly Extension[], deps: HostDeps): Ho
 			getAuthProvider(id: string) {
 				return authProviders.get(id);
 			},
+			getExtensions() {
+				return Object.freeze(activated.map((e) => e.manifest));
+			},
 			scheduler: {
 				register(job: ScheduledJob) {
 					scheduledJobs.push(job);
@@ -213,6 +217,9 @@ export function createHost(extensions: readonly Extension[], deps: HostDeps): Ho
 		getDisabled() {
 			return disabled;
 		},
+		getExtensions() {
+			return Object.freeze(activated.map((e) => e.manifest));
+		},
 		getHostAPI() {
 			return buildHostAPI("__host__", { registrationClosed: true });
 		},