diff --git a/frontend/src/spa/vertical-slice.ts b/frontend/src/spa/vertical-slice.ts
index 86d4301..f951e06 100644
--- a/frontend/src/spa/vertical-slice.ts
+++ b/frontend/src/spa/vertical-slice.ts
@@ -1,18 +1,15 @@
 import type { ApiClient } from '../api/client';
 import type { SessionDetailResponse } from '../api/types';
+import {
+  createSessionContextStore,
+  type SessionContext,
+  type SessionContextInput,
+  type SessionContextStore as PersistedSessionContextStore
+} from './session-context-store';
 
 export type AsyncState = 'idle' | 'loading' | 'success' | 'error';
 
-export interface SessionContext {
-  sessionCode: string;
-  playerToken: string;
-  nickname: string;
-}
-
-export interface SessionContextStore {
-  get(): SessionContext | null;
-  set(context: SessionContext): void;
-}
+export type SessionContextStore = Pick<PersistedSessionContextStore, 'get' | 'set'>;
 
 export interface VerticalSliceState {
   sessionCode: string;
@@ -30,14 +27,9 @@ export interface VerticalSliceController {
   startRound(sessionCode: string, categorySlug: string): Promise<VerticalSliceState>;
 }
 
-const NOOP_SESSION_CONTEXT_STORE: SessionContextStore = {
-  get: () => null,
-  set: () => undefined
-};
-
 export function createVerticalSliceController(
   api: ApiClient,
-  sessionContextStore: SessionContextStore = NOOP_SESSION_CONTEXT_STORE
+  sessionContextStore: SessionContextStore = createSessionContextStore()
 ): VerticalSliceController {
   const persistedContext = sessionContextStore.get();
 
@@ -96,11 +88,12 @@ export function createVerticalSliceController(
     state.joinState = 'success';
     state.sessionCode = normalizeCode(join.data.session.code || requestCode);
 
-    sessionContextStore.set({
+    const nextContext: SessionContextInput = {
       sessionCode: state.sessionCode,
-      playerToken: join.data.player.session_token,
-      nickname: join.data.player.nickname
-    });
+      playerId: join.data.player.id,
+      token: join.data.player.session_token
+    };
+    sessionContextStore.set(nextContext);
 
     return hydrateLobby(state.sessionCode);
   }
@@ -131,3 +124,5 @@ export function createVerticalSliceController(
     startRound
   };
 }
+
+export type { SessionContext };
diff --git a/frontend/tests/vertical-slice.test.ts b/frontend/tests/vertical-slice.test.ts
index fd588b4..a8a256d 100644
--- a/frontend/tests/vertical-slice.test.ts
+++ b/frontend/tests/vertical-slice.test.ts
@@ -68,11 +68,43 @@ function makeSessionContextStore(initial: SessionContext | null = null): Session
     get: vi.fn(() => value),
     set: vi.fn((next: SessionContext) => {
       value = next;
+      return next;
     })
   };
 }
 
 describe('vertical slice controller: lobby -> join -> start round', () => {
+  it('uses createSessionContextStore by default (no manual injection)', async () => {
+    vi.resetModules();
+    const defaultStore = {
+      get: vi.fn(() => null),
+      set: vi.fn((next: SessionContext) => next),
+      clear: vi.fn()
+    };
+
+    vi.doMock('../src/spa/session-context-store', async () => {
+      const actual = await vi.importActual<typeof import('../src/spa/session-context-store')>('../src/spa/session-context-store');
+      return {
+        ...actual,
+        createSessionContextStore: vi.fn(() => defaultStore)
+      };
+    });
+
+    const { createVerticalSliceController: createControllerWithMock } = await import('../src/spa/vertical-slice');
+    const api = makeApiMock();
+    const controller = createControllerWithMock(api);
+
+    await controller.joinLobby('ABCD12', 'Maja');
+
+    expect(defaultStore.set).toHaveBeenCalledWith({
+      sessionCode: 'ABCD12',
+      playerId: 9,
+      token: 'token-1'
+    });
+
+    vi.doUnmock('../src/spa/session-context-store');
+    vi.resetModules();
+  });
   it('tracks loading and success state for join + start flow', async () => {
     const api = makeApiMock();
     const controller = createVerticalSliceController(api);
@@ -102,8 +134,8 @@ describe('vertical slice controller: lobby -> join -> start round', () => {
 
     expect(sessionContextStore.set).toHaveBeenCalledWith({
       sessionCode: 'ABCD12',
-      playerToken: 'token-1',
-      nickname: 'Maja'
+      playerId: 9,
+      token: 'token-1'
     });
     expect(controller.getState().sessionCode).toBe('ABCD12');
   });
@@ -112,8 +144,8 @@ describe('vertical slice controller: lobby -> join -> start round', () => {
     const api = makeApiMock();
     const sessionContextStore = makeSessionContextStore({
       sessionCode: 'wxyz99',
-      playerToken: 'token-old',
-      nickname: 'Maja'
+      playerId: 5,
+      token: 'token-old'
     });
     const controller = createVerticalSliceController(api, sessionContextStore);