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);

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

@@ -1,5 +1,7 @@
 import { z } from "zod";
 
+import type { IEventBus } from "@repo/core-events";
+import { userSignedUpEvent } from "../../events/user-signed-up.event";
 import { AuthenticationError } from "../../entities/errors/auth";
 import { cookieSchema } from "../../entities/models/cookie";
 import { sessionSchema } from "../../entities/models/session";
@@ -34,6 +36,7 @@ export const signUpUseCase =
   (
     usersRepository: IUsersRepository,
     authenticationService: IAuthenticationService,
+    bus: IEventBus,
   ) =>
   async (input: SignUpInput): Promise<SignUpOutput> => {
     const existingUser = await usersRepository.getUserByUsername(input.username);
@@ -52,5 +55,13 @@ export const signUpUseCase =
 
     const { cookie, session } = await authenticationService.createSession(newUser);
 
+    // Auth is username-based — synthesize a deterministic email so the event
+    // payload validates against userSignedUpEventSchema.email().
+    await bus.publish(userSignedUpEvent, {
+      userId: newUser.id,
+      email: `${newUser.username}@example.local`,
+      signedUpAt: new Date().toISOString(),
+    });
+
     return signUpOutputSchema.parse({ session, cookie });
   };

packages/auth/src/di/bind-dev-seed.ts

@@ -81,7 +81,7 @@ export async function bindDevSeedAuth(
     withCapture(
       logger,
       { feature: "auth", layer: "use-case", name: "auth.signUp" },
-      signUpUseCase(repo, authService),
+      signUpUseCase(repo, authService, bus),
     ),
   );
   const wrappedSignOut = withSpan(

packages/auth/src/di/bind-production.ts

@@ -74,7 +74,7 @@ export function bindProductionAuth(
     withCapture(
       logger,
       { feature: "auth", layer: "use-case", name: "auth.signUp" },
-      signUpUseCase(repo, authService),
+      signUpUseCase(repo, authService, bus),
     ),
   );
   const wrappedSignOut = withSpan(

packages/auth/src/di/module.ts

@@ -1,4 +1,5 @@
 import { ContainerModule, type interfaces } from "inversify";
+import { InMemoryEventBus } from "@repo/core-events";
 
 import type { IUsersRepository } from "../application/repositories/users.repository.interface";
 import type { IAuthenticationService } from "../application/services/authentication.service.interface";
@@ -44,9 +45,13 @@ export const AuthModule = new ContainerModule((bind: interfaces.Bind) => {
   );
 
   bind<ISignUpUseCase>(AUTH_SYMBOLS.ISignUpUseCase).toDynamicValue((ctx) =>
+    // Default fallback uses a fresh InMemoryEventBus — real cross-feature
+    // wiring runs through bindProductionAuth / bindDevSeedAuth where the
+    // bindAll() dispatcher passes a shared bus instance.
     signUpUseCase(
       ctx.container.get<IUsersRepository>(AUTH_SYMBOLS.IUsersRepository),
       ctx.container.get<IAuthenticationService>(AUTH_SYMBOLS.IAuthenticationService),
+      new InMemoryEventBus(),
     ),
   );
 

packages/auth/src/interface-adapters/controllers/sign-up.controller.test.ts

@@ -1,4 +1,5 @@
 import { describe, it, expect } from "vitest";
+import { RecordingEventBus } from "@repo/core-testing/instrumentation";
 import { signUpController } from "@/interface-adapters/controllers/sign-up.controller";
 import { MockUsersRepository } from "@/infrastructure/repositories/users.repository.mock";
 import { MockAuthenticationService } from "@/infrastructure/services/authentication.service.mock";
@@ -10,7 +11,7 @@ describe("signUpController", () => {
   it("returns a cookie on successful sign-up", async () => {
     const users = new MockUsersRepository([]);
     const auth = new MockAuthenticationService(users);
-    const useCase = signUpUseCase(users, auth);
+    const useCase = signUpUseCase(users, auth, new RecordingEventBus());
     const controller = signUpController(useCase);
 
     const result = await controller({
@@ -25,7 +26,7 @@ describe("signUpController", () => {
   it("throws InputParseError when passwords do not match", async () => {
     const users = new MockUsersRepository([]);
     const auth = new MockAuthenticationService(users);
-    const useCase = signUpUseCase(users, auth);
+    const useCase = signUpUseCase(users, auth, new RecordingEventBus());
     const controller = signUpController(useCase);
 
     await expect(
@@ -41,7 +42,7 @@ describe("signUpController", () => {
     const users = new MockUsersRepository([]);
     const auth = new MockAuthenticationService(users);
     await users.createUser(userFactory.build({ username: "alice" }));
-    const useCase = signUpUseCase(users, auth);
+    const useCase = signUpUseCase(users, auth, new RecordingEventBus());
     const controller = signUpController(useCase);
 
     await expect(