feat(auth): signUp publishes userSignedUpEvent

signUpUseCase now takes an IEventBus and publishes userSignedUpEvent
after creating the user (synthesizing email from username since auth
is username-based). Use case mocks-default in module.ts get a fresh
InMemoryEventBus per resolution; bind-production / bind-dev-seed wire
the shared bus passed by bindAll. Tests updated to inject
RecordingEventBus, including a new test that asserts publish on
success and silence on failure.

packages/auth/src/application/use-cases/sign-up.use-case.test.ts

@@ -1,5 +1,6 @@
 import { describe, it, expect } from "vitest";
 import { ZodError } from "zod";
+import { RecordingEventBus } from "@repo/core-testing/instrumentation";
 import { signUpUseCase, signUpOutputSchema } from "@/application/use-cases/sign-up.use-case";
 import { MockUsersRepository } from "@/infrastructure/repositories/users.repository.mock";
 import { MockAuthenticationService } from "@/infrastructure/services/authentication.service.mock";
@@ -11,7 +12,8 @@ describe("signUpUseCase", () => {
   it("creates a new user and returns session + cookie", async () => {
     const users = new MockUsersRepository([]);
     const auth = new MockAuthenticationService(users);
-    const useCase = signUpUseCase(users, auth);
+    const bus = new RecordingEventBus();
+    const useCase = signUpUseCase(users, auth, bus);
 
     const result = await useCase({
       username: "carol",
@@ -26,13 +28,50 @@ describe("signUpUseCase", () => {
   it("throws AuthenticationError when username taken", async () => {
     const users = new MockUsersRepository([]);
     const auth = new MockAuthenticationService(users);
+    const bus = new RecordingEventBus();
     await users.createUser(userFactory.build({ username: "alice" }));
 
-    const useCase = signUpUseCase(users, auth);
+    const useCase = signUpUseCase(users, auth, bus);
     await expect(
       useCase({ username: "alice", password: "secret_password", confirmPassword: "secret_password" }),
     ).rejects.toBeInstanceOf(AuthenticationError);
   });
+
+  it("publishes auth.user.signed-up after creating the user", async () => {
+    const users = new MockUsersRepository([]);
+    const auth = new MockAuthenticationService(users);
+    const bus = new RecordingEventBus();
+    const useCase = signUpUseCase(users, auth, bus);
+
+    await useCase({
+      username: "dave",
+      password: "secret_password",
+      confirmPassword: "secret_password",
+    });
+
+    expect(bus.published).toHaveLength(1);
+    const published = bus.published[0]!;
+    expect(published.name).toBe("auth.user.signed-up");
+    expect(published.payload).toEqual(
+      expect.objectContaining({
+        userId: expect.any(String),
+        email: expect.stringMatching(/^dave@/),
+      }),
+    );
+  });
+
+  it("does NOT publish when sign-up fails (username taken)", async () => {
+    const users = new MockUsersRepository([]);
+    const auth = new MockAuthenticationService(users);
+    const bus = new RecordingEventBus();
+    await users.createUser(userFactory.build({ username: "eve" }));
+
+    const useCase = signUpUseCase(users, auth, bus);
+    await expect(
+      useCase({ username: "eve", password: "secret_password", confirmPassword: "secret_password" }),
+    ).rejects.toBeInstanceOf(AuthenticationError);
+    expect(bus.published).toHaveLength(0);
+  });
 });
 
 describe("signUpUseCase output validation (R25)", () => {
@@ -46,7 +85,8 @@ describe("signUpUseCase output validation (R25)", () => {
       createSession: async () => ({ session: { id: 123 }, cookie: null }),
     } as unknown as IAuthenticationService;
 
-    const useCase = signUpUseCase(users, auth);
+    const bus = new RecordingEventBus();
+    const useCase = signUpUseCase(users, auth, bus);
     await expect(
       useCase({ username: "carol", password: "secret_password", confirmPassword: "secret_password" }),
     ).rejects.toBeInstanceOf(ZodError);