2 files changed, 72 insertions, 1 deletions

diff --git a/packages/kernel/src/host/host.test.ts b/packages/kernel/src/host/host.test.ts
index 82d5177..11c2356 100644
--- a/packages/kernel/src/host/host.test.ts
+++ b/packages/kernel/src/host/host.test.ts
@@ -687,4 +687,67 @@ describe("createHost", () => {
 			expect(host.getDisabled()).toHaveLength(0);
 		});
 	});
+
+	describe("getHostAPI", () => {
+		it("returns a HostAPI whose read-views reflect registrations from activation", async () => {
+			const tool = createFakeTool("read-file");
+			const provider = createFakeProvider("anthropic");
+			const auth = createFakeAuth("apikey");
+
+			const ext = createExtension("multi-ext", {
+				activate: (host) => {
+					host.defineTool(tool);
+					host.defineProvider(provider);
+					host.defineAuth(auth);
+				},
+			});
+
+			const host = createHost([ext], deps);
+			await host.activate();
+
+			const api = host.getHostAPI();
+
+			expect(api.getTools().size).toBe(1);
+			expect(api.getTools().get("read-file")).toBe(tool);
+
+			expect(api.getProviders().size).toBe(1);
+			expect(api.getProviders().get("anthropic")).toBe(provider);
+
+			expect(api.getAuthProviders().size).toBe(1);
+			expect(api.getAuthProvider("apikey")).toBe(auth);
+		});
+
+		it("throws on defineTool after activation", async () => {
+			const ext = createExtension("ext", { activate: () => {} });
+			const host = createHost([ext], deps);
+			await host.activate();
+
+			const api = host.getHostAPI();
+			expect(() => api.defineTool(createFakeTool("late"))).toThrow(
+				"Registration not available after activation",
+			);
+		});
+
+		it("throws on defineProvider after activation", async () => {
+			const ext = createExtension("ext", { activate: () => {} });
+			const host = createHost([ext], deps);
+			await host.activate();
+
+			const api = host.getHostAPI();
+			expect(() => api.defineProvider(createFakeProvider("late"))).toThrow(
+				"Registration not available after activation",
+			);
+		});
+
+		it("throws on defineAuth after activation", async () => {
+			const ext = createExtension("ext", { activate: () => {} });
+			const host = createHost([ext], deps);
+			await host.activate();
+
+			const api = host.getHostAPI();
+			expect(() => api.defineAuth(createFakeAuth("late"))).toThrow(
+				"Registration not available after activation",
+			);
+		});
+	});
 });
diff --git a/packages/kernel/src/host/host.ts b/packages/kernel/src/host/host.ts
index 8592a16..dd61f9f 100644
--- a/packages/kernel/src/host/host.ts
+++ b/packages/kernel/src/host/host.ts
@@ -54,6 +54,7 @@ export interface Host {
 	readonly getScheduledJobs: () => readonly ScheduledJob[];
 	readonly getMigrations: () => readonly string[];
 	readonly getDisabled: () => readonly DisabledExtension[];
+	readonly getHostAPI: () => HostAPI;
 }
 
 export function createHost(extensions: readonly Extension[], deps: HostDeps): Host {
@@ -95,15 +96,19 @@ export function createHost(extensions: readonly Extension[], deps: HostDeps): Ho
 		}
 	}
 
-	function buildHostAPI(): HostAPI {
+	function buildHostAPI(opts?: { readonly registrationClosed?: boolean }): HostAPI {
+		const closed = opts?.registrationClosed ?? false;
 		return {
 			defineTool(tool: ToolContract) {
+				if (closed) throw new Error("Registration not available after activation");
 				tools.set(tool.name, tool);
 			},
 			defineProvider(provider: ProviderContract) {
+				if (closed) throw new Error("Registration not available after activation");
 				providers.set(provider.id, provider);
 			},
 			defineAuth(auth: AuthContract) {
+				if (closed) throw new Error("Registration not available after activation");
 				authProviders.set(auth.id, auth);
 			},
 			on<TPayload>(hook: EventHookDescriptor<TPayload>, handler: EventHandler<TPayload>) {
@@ -201,5 +206,8 @@ export function createHost(extensions: readonly Extension[], deps: HostDeps): Ho
 		getDisabled() {
 			return disabled;
 		},
+		getHostAPI() {
+			return buildHostAPI({ registrationClosed: true });
+		},
 	};
 }