diff --git a/.kilo/plans/880.md b/.kilo/plans/880.md
deleted file mode 100644
index b5d78b0..0000000
--- a/.kilo/plans/880.md
+++ /dev/null
@@ -1,30 +0,0 @@
-# Implementation Plan: Authenticated Shell LED Visibility Fix
-
-## 1. Architectural Reconnaissance
-- **Codebase style & conventions:** Node.js monorepo with an Angular 17 standalone-component SPA and NestJS backend. The authenticated shell uses OnPush components, signal inputs/outputs, inline Angular templates/styles, and theme CSS custom properties. `HomeComponent` owns event-stream lifecycle and passes `EventStatusStore.state()` into the presentational `ShellHeaderComponent`. Quick tabs and change-password behavior are already implemented and are not implicated in this regression.
-- **Data Layer:** TypeORM-backed backend settings provide `eventStartUtc` and `eventEndUtc`; no schema or persistence changes are required. The backend event-state calculation and authenticated SSE payload are already functioning: the shell receives the correct `running`, `countdown`, `stopped`, or `unconfigured` state and applies the matching class.
-- **Test Framework & Structure:** Root Jest 29 multi-project configuration with `ts-jest`; frontend tests run in jsdom from the dedicated `tests/frontend/` directory. `npm test` runs all backend and frontend tests, while `npm run test:frontend` runs the frontend project only. Existing `tests/frontend/shell-led.spec.ts` is a source-structure assertion and does not instantiate the component or verify the rendered style binding.
-- **Required Tools & Dependencies:** No new system tools, global CLIs, npm packages, persistent `/data` assets, or `setup.sh` changes are required. Existing Angular, Jest, jsdom, and TypeScript dependencies are sufficient.
-
-## 2. Impacted Files
-- **To Modify:**
-  - `frontend/src/app/features/shell/header/shell-header.component.ts` — remove the conflicting transparent base declaration and bind the state-specific background color directly on the LED element so the browser paints the themed color reliably.
-  - `tests/frontend/shell-led.spec.ts` — replace/extend brittle source-only assertions with a focused automated regression covering the style value produced for each event state and preserving the accessible state label.
-- **To Create:** None.
-
-## 3. Proposed Changes
-1. **Database / Schema Migration:** None. Event timestamps, settings storage, REST/SSE contracts, and backend state computation remain unchanged.
-2. **Backend Logic & APIs:** None. `/api/v1/events/status` already emits the correct state, and `EventStatusStore` already forwards it to the shell.
-3. **Frontend UI Integration:**
-   1. In `ShellHeaderComponent`, define a typed state-to-theme-color mapping for all `EventState` values: `running` → `var(--color-success)`, `countdown` → `var(--color-warning)`, `stopped` → `var(--color-danger)`, and `unconfigured` → `var(--color-secondary)`.
-   2. Replace the unused `ledClass` computed value with a computed background-color value derived from `eventState()`; keep the existing state class bindings because they are useful selectors and preserve the current DOM contract.
-   3. Bind the computed value directly to the LED span's `style.background-color`. This gives the element an explicit non-transparent author value while continuing to resolve the active theme token at runtime, matching the reported proof that a direct targeted declaration makes the dot visible.
-   4. Remove `background-color: transparent` from the component base `.led` rule, and remove the redundant component state-color declarations if the inline binding becomes the single authoritative color source. Retain only the shape/layout styling (`inline-block`, 10×10 dimensions, circular radius, border, alignment).
-   5. Remove the global LED state rules from `frontend/src/styles.css` if they are no longer consumed, avoiding duplicate ownership and future cascade ambiguity; keep canonical theme token declarations untouched.
-   6. Preserve the existing `data-testid`, four state classes, and `aria-label="Event status: <state>"`, so status remains exposed textually rather than by color alone.
-   7. Do not modify `HomeComponent`, `QuickTabsComponent`, change-password components, event store, routes, SSE transport, or backend services because repository tracing shows those layers already deliver the correct state and shell behavior.
-
-## 4. Test Strategy
-- **Target Unit Test File:** `tests/frontend/shell-led.spec.ts`.
-- **Mocking Strategy:** No backend, HTTP, SSE, timers, filesystem fixtures, browser automation, or persistent data. Exercise a small exported pure state-to-color helper (or equivalent component mapping) with table-driven assertions for the four states, and retain focused source/template assertions that the LED consumes that value through `[style.background-color]`, keeps each state class binding, and keeps the dynamic `aria-label`. This directly prevents a regression to a transparent base color while remaining fast and CLI-only under `npm test`.
-- **Verification Commands for the implementer:** Run `npm run test:frontend`, `npm test`, and `npm run build` from `/repo`. The root build compiles both Angular and NestJS; no separate lint or typecheck script is defined.
diff --git a/.kilo/plans/881.md b/.kilo/plans/881.md
new file mode 100644
index 0000000..f1ba835
--- /dev/null
+++ b/.kilo/plans/881.md
@@ -0,0 +1,45 @@
+# Implementation Plan: Job 881 — Cross-Tab Authenticated Shell Invalidation
+
+## 1. Architectural Reconnaissance
+- **Codebase style & conventions:** TypeScript monorepo with an Angular standalone-component SPA and NestJS API. Frontend services are root-provided Angular injectables using signals, `inject()`, async/await, and typed HTTP calls. Authentication state is held in `AuthService` signals and mirrored to per-tab `sessionStorage`; `HomeComponent` owns the authenticated shell and starts/stops the authenticated event stream. The route tree protects `/`, `/challenges`, `/scoreboard`, and `/blog` through the parent `authGuard`.
+- **Data Layer:** No database/schema change is required. The server-side logout endpoint already revokes/clears the refresh-cookie state; this job is a browser-context propagation fix. Existing frontend persistence uses `sessionStorage`, which is intentionally tab-scoped and therefore cannot notify sibling tabs. A cross-tab browser event channel should carry an invalidation notification without carrying access tokens or user data.
+- **Test Framework & Structure:** Root Jest 29 with two projects in `tests/jest.config.js`; frontend tests run in jsdom through `npm test` or `npm run test:frontend`. Tests are already centralized under `tests/frontend`, never beside source. Existing tests are mostly focused TypeScript/pure-contract tests, and `authenticated-event-source.spec.ts` models fetch/SSE boundaries because Angular runtime modules are difficult for the current Jest transform. Add only small logic tests for the notification/listener behavior and source error handling.
+- **Required Tools & Dependencies:** No new system tools, npm packages, database migrations, or `setup.sh` changes are expected. `BroadcastChannel` and/or the `storage` event are browser platform APIs. The implementation should feature-detect the selected API and remain safe in jsdom/SSR-like contexts. Existing Node/npm/Jest/TypeScript setup is sufficient.
+
+## 2. Impacted Files
+- **To Modify:**
+  - `frontend/src/app/core/services/auth.service.ts` — publish a same-browser-context session-invalidation event after local logout/clear and subscribe to peer-tab invalidation events so every tab clears its in-memory and tab-local state.
+  - `frontend/src/app/core/services/authenticated-event-source.service.ts` — distinguish an unauthorized SSE response (`401`, and optionally other auth-failure statuses according to the existing API contract) from generic transport failure and expose it through the existing `error` event contract, or otherwise provide a single auth-invalidation callback path to `AuthService`.
+  - `frontend/src/app/core/services/event-status.store.ts` — register an `error` listener for the authenticated event source and invoke the auth invalidation path on unauthorized stream failure; ensure `stop()` removes/neutralizes the listener and remains idempotent.
+  - `frontend/src/app/features/home/home.component.ts` — react to the centralized auth state becoming unauthenticated, stop/reset shell-owned state as needed, and navigate to `/login` without requiring a quick-tab interaction or reload; avoid duplicate navigation when the local logout already performed it.
+- **To Create:**
+  - `tests/frontend/auth-cross-tab.spec.ts` — focused tests for cross-tab invalidation publication/consumption and duplicate/self-origin behavior using mocked browser channel/storage boundaries.
+  - If the implementer chooses a pure transport result rather than a direct callback, optionally `frontend/src/app/core/services/auth-session-events.pure.ts` and its corresponding test file; prefer keeping the event-name/payload validation pure and small rather than introducing an unnecessary abstraction.
+- **Not to Modify:** Backend controllers, refresh-token schema/migrations, shell markup, quick-tab components, routes, or `setup.sh`; the server invalidation and route protection already exist.
+
+## 3. Proposed Changes
+1. **Database / Schema Migration:**
+   - No migration. Confirm the existing `POST /api/v1/auth/logout` behavior remains the source of truth for server-side refresh-cookie invalidation.
+   - Do not broadcast JWTs, refresh tokens, usernames, or arbitrary storage contents. Broadcast only a fixed event type (for example, a namespaced `logout`/`session-invalidated` message) and optionally a random per-tab sender identifier if needed to avoid self-processing.
+
+2. **Backend Logic & APIs:**
+   - No backend endpoint changes. The existing authenticated logout endpoint is called by `AuthService.logout()` before local state is cleared, and hard navigation already proves the server clears the refresh cookie.
+   - Treat an authenticated SSE response with `401` as evidence that the current tab’s session is invalid. Update `AuthenticatedEventSourceService`’s internal fetch path so the response status is available to the existing `error` dispatch, without exposing response bodies or credentials. Generic network/stream errors should remain generic unless the response explicitly indicates unauthorized.
+   - If the transport contract cannot safely distinguish error categories through `Event`, add a minimal typed error event/detail or a separate `unauthorized` listener type in `event-status.pure.ts`; update all implementations and tests consistently. Keep the contract framework-light and compatible with the current custom fetch-based EventSource implementation.
+
+3. **Frontend UI Integration:**
+   - Centralize cross-tab handling in `AuthService`, because it owns the authoritative `isAuthenticated`, access-token, and session-storage state. Initialize one browser listener for the root singleton, feature-detect `BroadcastChannel`, and provide a fallback using a namespaced `localStorage` key plus the browser `storage` event if BroadcastChannel is unavailable. If both are installed, publish on the primary channel and retain the fallback only if necessary; avoid double-processing identical notifications.
+   - On a local logout, call the server as today, then clear local state and publish the invalidation signal. Ensure peer-tab handling calls a non-broadcasting local-clear method so the notification does not echo indefinitely. The local tab may also receive its own channel message in some test/browser implementations, so make handling idempotent.
+   - On a peer invalidation, clear the access token, current user, and `sessionStorage`; make the state transition observable to consumers. If `AuthService.clear()` is reused by refresh failure or other local failures, define whether those paths should broadcast as well; the preferred rule is that any confirmed local session invalidation broadcasts, while a peer-originated clear suppresses rebroadcast.
+   - Wire the authenticated SSE lifecycle to the same invalidation path. `EventStatusStore.start()` should attach both message and error listeners. When the authenticated event source reports `401`, invoke an injected/session-invalidation callback or call an explicit `AuthService` method; then close the stream. Do not redirect merely for transient network errors, malformed frames, or ordinary stream closure.
+   - In `HomeComponent`, observe the auth signal or subscribe to a narrow invalidation event and navigate to `/login` after a peer logout/SSE unauthorized result. Reset `UserStore`, close the event stream, close open menus/modals if appropriate, and use a navigation guard/flag so the local `onLogout()` path does not trigger duplicate navigation. The next click on Challenges, Scoreboard, or Blog must not be able to continue rendering authenticated content; the route guard should see `isAuthenticated === false` and return the existing login `UrlTree`.
+   - Ensure cleanup: close `BroadcastChannel`, remove `storage` listeners, and detach/neutralize SSE listeners during service/component destruction or `stop()`. Preserve the existing event countdown behavior and shell UI when authentication remains valid.
+   - Keep browser API access guarded for non-browser/test environments. Use the existing Angular DI/signal conventions; do not add a third-party messaging library or move tokens into `localStorage`.
+
+## 4. Test Strategy
+- **Target Unit Test File:** `tests/frontend/auth-cross-tab.spec.ts` for the core event protocol and AuthService behavior. Extend `tests/frontend/authenticated-event-source.spec.ts` only with the minimal unauthorized-response contract test if that file remains the established transport boundary. If direct Angular service instantiation is impractical under the current Jest setup, extract a small pure event encoder/decoder and test it directly, while testing the transport contract with the existing fetch mock style.
+- **Mocking Strategy:**
+  - Mock `BroadcastChannel` with an in-memory registry of channel instances, recording `postMessage`, `addEventListener`, `removeEventListener`, and `close`; deliver messages only to peer instances to model browser behavior and separately cover a self-delivery implementation.
+  - Mock `window.localStorage` and dispatch synthetic `StorageEvent` objects for the fallback path. Assert the implementation only accepts the fixed namespaced key/event shape and ignores malformed or unrelated storage changes.
+  - Use a minimal fake `AuthService` or explicit test doubles for token/user/session-storage operations where testing `EventStatusStore`; use a fake `EventSourceLike` that records listeners and close calls to verify `401` causes invalidation and generic errors do not.
+  - Cover only the core success and directly relevant failure paths: local logout publishes once and clears state; peer notification clears state without rebroadcast; fallback storage notification works when BroadcastChannel is absent; malformed/unrelated messages are ignored; unauthorized SSE invalidates and closes; generic SSE error preserves authentication. Run through the existing root `npm test` command; no browser/UI or persistent `/data` fixture is needed.
diff --git a/docs/architecture/frontend-structure.md b/docs/architecture/frontend-structure.md
index fe086d4..6bb2cce 100644
--- a/docs/architecture/frontend-structure.md
+++ b/docs/architecture/frontend-structure.md
@@ -3,7 +3,7 @@ type: architecture
 title: Frontend Structure
 description: Angular routes, components, services, guards, interceptors, and authenticated SSE transport.
 tags: [architecture, frontend, angular, shell, sse]
-timestamp: 2026-07-22T09:35:00Z
+timestamp: 2026-07-22T10:32:00Z
 ---
 
 # Routes
@@ -24,13 +24,14 @@ Routes live in `frontend/src/app/app.routes.ts`:
 
 | Symbol | Path | Responsibility |
 |---|---|---|
-| `HomeComponent` | `frontend/src/app/features/home/home.component.ts` | Smart shell; owns navigation signals, user hydration, change-password flow, and event-stream lifecycle. |
+| `HomeComponent` | `frontend/src/app/features/home/home.component.ts` | Smart shell; owns navigation signals, user hydration, change-password flow, event-stream lifecycle, and peer-invalidation subscription. |
 | `ShellHeaderComponent` | `frontend/src/app/features/shell/header/shell-header.component.ts` | Renders title, active section, event LED/countdown, and user menu; contains component-scoped LED styling. |
 | `QuickTabsComponent` | `frontend/src/app/features/shell/tabs/quick-tabs.component.ts` | Emits navigation events for Challenges, Scoreboard, and Blog. |
-| `EventStatusStore` | `frontend/src/app/core/services/event-status.store.ts` | Applies event state frames and computes countdown text; re-exports the pure LED color mapping. |
-| `AuthenticatedEventSourceService` | `frontend/src/app/core/services/authenticated-event-source.service.ts` | Opens authenticated SSE over `fetch`, parsing streamed frames into `EventSourceLike` events. |
-| `AuthService` | `frontend/src/app/core/services/auth.service.ts` | Stores the access token used by the authenticated SSE transport. |
+| `EventStatusStore` | `frontend/src/app/core/services/event-status.store.ts` | Applies event state frames and computes countdown text; re-exports the pure LED color mapping; wires an optional `onUnauthorized` callback for the new SSE `401`/`403` event. |
+| `AuthenticatedEventSourceService` | `frontend/src/app/core/services/authenticated-event-source.service.ts` | Opens authenticated SSE over `fetch`, parsing streamed frames into `EventSourceLike` events; dispatches a separate `'unauthorized'` event for `401`/`403`. |
+| `AuthService` | `frontend/src/app/core/services/auth.service.ts` | Stores the access token used by the authenticated SSE transport; owns the cross-tab invalidation `BroadcastChannel` + `storage`-event fallback and exposes `clearAndBroadcast` / `onPeerInvalidation`. |
 | `UserStore` | `frontend/src/app/core/services/user.store.ts` | Hydrates the signed-in user and rank data. |
+| `auth-session-events.pure.ts` | `frontend/src/app/core/services/auth-session-events.pure.ts` | Pure cross-tab message encoding/validation and the namespaced channel / storage-key constants. |
 
 # Authenticated SSE wiring
 
@@ -44,10 +45,17 @@ Routes live in `frontend/src/app/app.routes.ts`:
 4. Splits complete SSE records on blank lines, joins repeated `data:` lines, and
    dispatches `MessageEvent` objects.
 5. Buffers records received before the message listener is attached.
-6. Aborts and clears listeners when `close()` is called.
+6. Inspects the response status *before* the `ok`/`body` check; on `401` or
+   `403` dispatches a separate `'unauthorized'` event and returns without
+   reading the body. Generic transport failures still dispatch `'error'`.
+7. Aborts and clears listeners when `close()` is called.
 
-`EventStatusStore` parses each message as `EventStatePayload`, updates its signals,
-and runs a one-second local timer. `HomeComponent` stops the store on destruction.
+`EventStatusStore.start(createSource, onUnauthorized?)` parses each message as
+`EventStatePayload`, updates its signals, runs a one-second local timer, and —
+when `onUnauthorized` is provided — invokes it on `'unauthorized'` events.
+`HomeComponent` passes an `onUnauthorized` callback that delegates to its
+shared `handleSessionInvalidated('sse-unauthorized')` flow and stops the store
+on destruction.
 
 # Key integration files
 
@@ -84,6 +92,20 @@ color always comes from `LED_COLOR_BY_STATE` and is guaranteed to be a
 non-transparent theme token. The four `led-<state>` classes remain on the
 element as selectors/test hooks but no longer own the color.
 
+# Cross-tab session invalidation
+
+`AuthService` (constructed once at root) installs a single
+`BroadcastChannel('hipctf.auth.v1')` and a `localStorage` `storage`-event
+fallback. The shape of the broadcast payload is defined in
+`auth-session-events.pure.ts` and contains only `{ type, origin, ts }` — no
+tokens or user data. `clearAndBroadcast()` is invoked from `logout()` and
+from the SSE unauthorized callback; peer listeners clear their local state
+without rebroadcasting. `HomeComponent` subscribes via
+`auth.onPeerInvalidation(...)`, resets `UserStore`, closes any open shell
+overlays, and navigates to `/login`. See
+[Cross-Tab Authenticated Shell Invalidation](/guides/cross-tab-invalidation.md)
+for the full contract and tester matrix.
+
 # See also
 
 - [Authenticated Shell](/guides/authenticated-shell.md)
diff --git a/docs/architecture/key-files.md b/docs/architecture/key-files.md
index 33ab169..8f7e224 100644
--- a/docs/architecture/key-files.md
+++ b/docs/architecture/key-files.md
@@ -3,7 +3,7 @@ type: architecture
 title: Key Files Index
 description: One-line responsibility for important source files, including authenticated event streaming.
 tags: [architecture, index, key-files]
-timestamp: 2026-07-22T09:35:00Z
+timestamp: 2026-07-22T10:32:00Z
 ---
 
 # Backend
@@ -31,14 +31,17 @@ timestamp: 2026-07-22T09:35:00Z
 | `frontend/src/app/app.routes.ts` | Defines public, shell, child, and admin routes. |
 | `frontend/src/app/app.component.ts` | Loads bootstrap data and restores the session. |
 | `frontend/src/app/features/home/home.component.ts` | Authenticated shell container; starts user and event state services. |
-| `frontend/src/app/core/services/auth.service.ts` | Signal-backed access token and current-user state. |
-| `frontend/src/app/core/services/authenticated-event-source.service.ts` | Fetch-based authenticated SSE transport with frame parsing and abort support. |
-| `frontend/src/app/core/services/event-status.store.ts` | Event state signal store and one-second countdown timer. |
-| `frontend/src/app/core/services/event-status.pure.ts` | Event payload types, pure countdown helpers, and the `LED_COLOR_BY_STATE` map used by the shell LED. |
+| `frontend/src/app/core/services/auth.service.ts` | Signal-backed access token and current-user state; owns the cross-tab invalidation `BroadcastChannel` + `storage`-event fallback. |
+| `frontend/src/app/core/services/auth-session-events.pure.ts` | Pure cross-tab message encoding/validation and namespaced constants used by the auth broadcast channel. |
+| `frontend/src/app/core/services/authenticated-event-source.service.ts` | Fetch-based authenticated SSE transport with frame parsing, abort support, and a separate `'unauthorized'` event for `401`/`403`. |
+| `frontend/src/app/core/services/event-status.store.ts` | Event state signal store, one-second countdown timer, and the optional `onUnauthorized` callback wiring. |
+| `frontend/src/app/core/services/event-status.pure.ts` | Event payload types, transport interface (including `'unauthorized'` listener), pure countdown helpers, and the `LED_COLOR_BY_STATE` map used by the shell LED. |
+| `frontend/src/app/features/home/home.component.ts` | Authenticated shell container; starts user and event state services, subscribes to peer invalidation, and navigates to `/login` when the session is invalidated elsewhere. |
 | `frontend/src/app/features/shell/header/shell-header.component.ts` | Shell title, status LED (size/shape only — color comes from the pure map via `[style.background-color]`), countdown, and user menu. |
 | `frontend/src/app/features/shell/tabs/quick-tabs.component.ts` | Main shell navigation tabs. |
 | `frontend/src/app/features/shell/change-password/change-password-modal.component.ts` | Change-password form modal. |
-| `tests/frontend/authenticated-event-source.spec.ts` | Tests SSE authorization and frame transport behavior. |
+| `tests/frontend/authenticated-event-source.spec.ts` | Tests SSE authorization, frame transport behavior, and the `401`/`403` unauthorized path. |
+| `tests/frontend/auth-session-events.spec.ts` | Pure tests for cross-tab invalidation message encoding, payload validation, and `storage`-event filtering. |
 
 # See also
 
diff --git a/docs/guides/authenticated-shell.md b/docs/guides/authenticated-shell.md
index 00f0bae..30baa9c 100644
--- a/docs/guides/authenticated-shell.md
+++ b/docs/guides/authenticated-shell.md
@@ -106,6 +106,22 @@ error event. The shell retains the last event state until a later connection suc
 1. Click each quick tab and confirm the matching route and active styling.
 2. Open the user menu and click **Logout**.
 3. Confirm navigation to `/login` and that the event stream is closed.
+4. With **two open tabs** of the same browser profile both on authenticated
+   routes, log out in one. Confirm the *other* tab also navigates to `/login`
+   without any user interaction. See
+   [Cross-Tab Authenticated Shell Invalidation](/guides/cross-tab-invalidation.md)
+   for the full tester matrix (peer logout, SSE unauthorized, negative cases).
+
+## Unauthorized SSE response
+
+1. Sign in once and open the authenticated shell.
+2. Trigger an unauthorized response on `/api/v1/events/status` (e.g. by
+   revoking the refresh cookie via an admin tool or by expiring the session
+   server-side).
+3. Confirm the shell clears, the event stream is closed, and the router
+   navigates to `/login`. The same flow in another open tab is propagated
+   via the cross-tab broadcast — see
+   [Cross-Tab Authenticated Shell Invalidation](/guides/cross-tab-invalidation.md).
 
 # See also
 
diff --git a/docs/guides/cross-tab-invalidation.md b/docs/guides/cross-tab-invalidation.md
new file mode 100644
index 0000000..7166db2
--- /dev/null
+++ b/docs/guides/cross-tab-invalidation.md
@@ -0,0 +1,204 @@
+---
+type: guide
+title: Cross-Tab Authenticated Shell Invalidation
+description: How logging out in one tab, or receiving an unauthorized SSE response, instantly logs out and redirects every other open tab of the SPA.
+tags: [guide, auth, session, broadcast-channel, storage-event, sse, tester]
+timestamp: 2026-07-22T10:32:00Z
+---
+
+# What this feature does
+
+Before this change, `sessionStorage` was tab-scoped, so logging out in **tab A**
+left any other open tabs (`/challenges`, `/scoreboard`, `/blog`, `/admin`)
+**still rendering authenticated content** until they were individually closed or
+reloaded. The same gap existed when the server returned `401` to the
+authenticated `/api/v1/events/status` SSE stream: the offending tab knew it was
+unauthenticated, but the others did not.
+
+This change adds a same-browser **cross-tab session-invalidation channel**:
+
+1. `AuthService` now owns a single `BroadcastChannel('hipctf.auth.v1')` plus a
+   `localStorage` `storage`-event fallback, registered in its constructor and
+   torn down on `DestroyRef`.
+2. Every confirmed local session invalidation (manual `logout()`, SSE
+   `401`/`403`) clears state **and publishes** a fixed-shape
+   `session-invalidated` message containing only the broadcasting tab's
+   `origin` (random per-tab UUID) and a `ts` timestamp. No tokens, users, or
+   storage contents are broadcast.
+3. Each tab listens for the message. If the `origin` differs from its own, it
+   treats the notification as a peer-logout: it clears its in-memory and
+   `sessionStorage` state **without** rebroadcasting, then notifies
+   subscribers.
+4. `HomeComponent` subscribes to the new peer-invalidation event, resets
+   `UserStore`, closes any open change-password / user-menu overlays, and
+   navigates to `/login`. A re-entrancy flag prevents duplicate navigations
+   when the originating tab already navigated.
+5. `AuthenticatedEventSourceService` was extended to dispatch a new
+   `'unauthorized'` event when the SSE fetch returns `401` or `403`. Generic
+   network failures still dispatch `'error'` and do **not** invalidate.
+
+# Why a new concept doc
+
+The change spans the auth core, the SSE transport, the event-status store, and
+the shell component. It introduces a new pure module
+(`auth-session-events.pure.ts`) and a new transport event type
+(`'unauthorized'` on `EventSourceLike`). A tester reading the
+[Authenticated Shell](/guides/authenticated-shell.md) guide should not have to
+re-derive the cross-tab propagation rules, and a developer wiring a new
+service should not have to read the auth service diff to learn about the
+broadcast contract.
+
+# Tester flows
+
+> Open the SPA in **two browser tabs** of the same browser profile, signed in
+> as the same user. Both tabs must be on authenticated routes (`/`,
+> `/challenges`, `/scoreboard`, `/blog`, or `/admin`).
+
+## Peer logout (manual)
+
+1. Sign in once and navigate to `/challenges` in **Tab A**.
+2. Duplicate the tab — **Tab B** opens at `/scoreboard`.
+3. In **Tab A**, open the user menu (`[data-testid="user-menu-trigger"]`)
+   and click **Logout**.
+4. **Tab A** navigates to `/login` (unchanged behavior).
+5. **Tab B** clears its shell state without any user interaction and navigates
+   to `/login`. The event LED, countdown, and quick-tab strip are no longer
+   visible — the landing/login view is shown.
+6. Confirm in DevTools → Application → Session Storage of **Tab B** that the
+   `hipctf.auth.v1` key has been removed.
+
+## Peer logout (SSE unauthorized)
+
+1. Sign in once and open the SPA in two tabs.
+2. In **Tab A** (server side, via an admin-only tool or by manually
+   revoking the refresh cookie), invalidate the refresh-cookie/session.
+3. Wait for `EventStatusStore` to reconnect — the SSE fetch returns `401`.
+4. **Tab A** clears state and navigates to `/login`.
+5. **Tab B** (still on `/challenges`) clears state and navigates to `/login`
+   without any SSE retry happening locally — it received the broadcast from
+   Tab A.
+
+> If you instead trigger the unauthorized response in **Tab B** directly
+> (e.g. by expiring the refresh cookie for that tab only), Tab B navigates
+> to `/login`; Tab A is unaffected.
+
+## Negative cases
+
+| Action | Expected |
+|---|---|
+| Open the SPA in a private/incognito window in addition to a normal window | Logging out in one does **not** affect the other. `BroadcastChannel` and the `storage` event are scoped to the browser profile. |
+| Trigger a generic network failure on `/api/v1/events/status` | The store dispatches `'error'`, retries, and **does not** invalidate. The shell keeps the last known event state. |
+| A non-HIPCTF tab on the same browser profile writes `hipctf.auth.invalidate.v1` to `localStorage` with garbage | The payload validator (`isCrossTabInvalidationEvent`) ignores it — no state change. |
+| Same tab echoes its own broadcast (test environment that delivers self-messages) | The `origin === crossTabOrigin` guard prevents self-processing and rebroadcast loops. |
+
+# Visual / interactive elements
+
+There are **no new UI controls**. Existing selectors continue to work and
+should be exercised after a peer invalidation:
+
+| Element | Selector | After peer invalidation |
+|---|---|---|
+| Shell header | `[data-testid="shell-header"]` | Removed from DOM by `Router` (route changed to `/login`). |
+| Quick tabs | `[data-testid="quick-tabs"]` | Removed from DOM by `Router`. |
+| User menu | `[data-testid="user-menu-trigger"]` | Removed from DOM by `Router`. |
+| Event LED / countdown | `[data-testid="shell-led"]`, `[data-testid="shell-countdown"]` | Removed from DOM by `Router`. |
+| Login form | `[data-testid="login-submit"]` | Becomes visible (already-tested flow). |
+
+# How it works (developer map)
+
+## Pure contract module
+
+`frontend/src/app/core/services/auth-session-events.pure.ts` is a
+framework-light, testable module that defines:
+
+| Export | Purpose |
+|---|---|
+| `CROSS_TAB_CHANNEL_NAME = 'hipctf.auth.v1'` | Stable `BroadcastChannel` name. |
+| `CROSS_TAB_STORAGE_KEY = 'hipctf.auth.invalidate.v1'` | `localStorage` fallback key. |
+| `CROSS_TAB_EVENT_TYPE = 'hipctf.session.invalidated'` | Marker used by the discriminated-union guard. |
+| `CrossTabInvalidationMessage` | `{ type: 'session-invalidated'; origin: string; ts: number }`. |
+| `encodeInvalidationMessage(origin)` | Builds a message stamped with `Date.now()`. |
+| `isCrossTabInvalidationMessage(value)` | Type-guard used by both `BroadcastChannel` and `storage` listeners. |
+| `isStorageInvalidationEvent(event)` | Guards `storage` events: only accepts the namespaced key with a parseable payload. |
+
+The payload intentionally carries **no** access token, refresh token, user id,
+or `sessionStorage` content.
+
+## `AuthService` wiring
+
+`frontend/src/app/core/services/auth.service.ts`
+
+* Constructor calls `installCrossTabListener()`, which:
+  * Feature-detects `BroadcastChannel`; if present, opens it on
+    `CROSS_TAB_CHANNEL_NAME` and subscribes to `'message'`.
+  * Always subscribes a `'storage'` listener filtered through
+    `isStorageInvalidationEvent`.
+* `clearAndBroadcast()` is the new public invalidation entry point: calls the
+  existing `clear()` (which wipes `sessionStorage`), and if
+  `suppressBroadcast` is `false`, publishes a fresh `encodeInvalidationMessage`
+  on both transports.
+* `logout()` now ends with `clearAndBroadcast()` instead of `clear()`.
+* `handleSseUnauthorized()` calls `clearAndBroadcast()` and then synchronously
+  notifies peer-invalidation subscribers with the reason
+  `'sse-unauthorized'` so the originating tab can navigate immediately.
+* `onPeerInvalidation(cb)` registers a subscriber; returns an unsubscribe
+  closure. Used by `HomeComponent`.
+* `handlePeerInvalidation()` is the single fan-in for both transport sources:
+  it parses the payload, drops self-origin messages, drops messages when the
+  tab is already unauthenticated, and runs `clear()` under
+  `suppressBroadcast = true` so the listener does not echo.
+* `DestroyRef.onDestroy` calls `teardownCrossTabListener()` which removes the
+  `'message'` and `'storage'` listeners and closes the channel.
+
+## Authenticated SSE: `unauthorized` event
+
+`frontend/src/app/core/services/authenticated-event-source.service.ts`
+
+The fetch path now inspects `res.status` *before* the `ok`/`body` check. If
+the status is `401` or `403`, the service dispatches a new `'unauthorized'`
+`Event` and returns; the response body is **not** read and no frame parsing
+runs.
+
+`frontend/src/app/core/services/event-status.pure.ts` widens
+`EventSourceLike.addEventListener` to accept `'open' | 'message' | 'error' |
+'unauthorized'`.
+
+`frontend/src/app/core/services/event-status.store.ts`
+
+`EventStatusStore.start(createSource, onUnauthorized?)` now accepts an
+optional second argument. When provided, the store attaches an
+`'unauthorized'` listener that invokes `onUnauthorized()` and is detached by
+`stop()` (which is already idempotent). Generic `'error'` events remain
+unhandled by the store; the SPA does not navigate on transport failure.
+
+## Shell reaction
+
+`frontend/src/app/features/home/home.component.ts`
+
+* `ngOnInit()` passes a second callback to `eventStatus.start(...)` that
+  delegates to `handleSessionInvalidated('sse-unauthorized')`.
+* It also subscribes to `auth.onPeerInvalidation(...)` and stores the
+  unsubscribe handle on `peerInvalidationUnsubscribe`.
+* `ngOnDestroy()` calls `eventStatus.stop()` and unsubscribes from
+  `onPeerInvalidation`.
+* `handleSessionInvalidated(reason)`:
+  * Calls `userStore.reset()` and closes `changePasswordOpen` /
+    `userMenuOpen` modal signals.
+  * Guards re-entry with `navigatingToLogin` and short-circuits when the
+    router is already on `/login`.
+  * Otherwise awaits `router.navigateByUrl('/login')`.
+
+## Test coverage
+
+| File | What it pins down |
+|---|---|
+| `tests/frontend/auth-session-events.spec.ts` | Pure payload validation, `storage`-event filtering, `encodeInvalidationMessage` shape. |
+| `tests/frontend/authenticated-event-source.spec.ts` | Extended: `401`/`403` dispatches `'unauthorized'`; generic errors still dispatch `'error'`; no body is read on the unauthorized path. |
+
+# See also
+
+- [Authenticated Shell](/guides/authenticated-shell.md)
+- [Session Restoration on Reload](/guides/session-restoration.md)
+- [Frontend Structure](/architecture/frontend-structure.md)
+- [REST API Overview](/api/rest-overview.md)
+- [Auth Endpoints](/api/auth.md)
diff --git a/docs/index.md b/docs/index.md
index 9efd50f..1d2dd11 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -11,7 +11,7 @@ scoreboard, an event window with a public countdown, theming, and admin
 controls.
 
 The docs below are organized by purpose so agents can pull just the slice
-they need. Last regenerated 2026-07-22T09:35:00Z.
+they need. Last regenerated 2026-07-22T10:32:00Z.
 
 # Architecture
 
@@ -65,6 +65,9 @@ they need. Last regenerated 2026-07-22T09:35:00Z.
 * [Change Password](/guides/change-password.md) - How a signed-in user
   changes their own password, including every error branch and the
   refresh-token revocation behavior.
+* [Cross-Tab Authenticated Shell Invalidation](/guides/cross-tab-invalidation.md) -
+  How a logout in one tab, or an unauthorized SSE response, instantly clears
+  and redirects every other open tab of the SPA.
 * [Session Restoration on Reload](/guides/session-restoration.md) - How
   the SPA keeps a user signed in across hard refreshes and how the
   guards wait for bootstrap + auth hydration before deciding where to
diff --git a/frontend/src/app/core/services/auth-session-events.pure.ts b/frontend/src/app/core/services/auth-session-events.pure.ts
new file mode 100644
index 0000000..b14f98a
--- /dev/null
+++ b/frontend/src/app/core/services/auth-session-events.pure.ts
@@ -0,0 +1,43 @@
+export const CROSS_TAB_CHANNEL_NAME = 'hipctf.auth.v1';
+export const CROSS_TAB_STORAGE_KEY = 'hipctf.auth.invalidate.v1';
+export const CROSS_TAB_EVENT_TYPE = 'hipctf.session.invalidated';
+
+export interface CrossTabInvalidationMessage {
+  type: 'session-invalidated';
+  origin: string;
+  ts: number;
+}
+
+export function encodeInvalidationMessage(origin: string): CrossTabInvalidationMessage {
+  return {
+    type: 'session-invalidated',
+    origin,
+    ts: Date.now(),
+  };
+}
+
+export function isCrossTabInvalidationMessage(
+  value: unknown,
+): value is CrossTabInvalidationMessage {
+  if (!value || typeof value !== 'object') return false;
+  const v = value as Record<string, unknown>;
+  return (
+    v['type'] === 'session-invalidated' &&
+    typeof v['origin'] === 'string' &&
+    typeof v['ts'] === 'number'
+  );
+}
+
+export function isStorageInvalidationEvent(
+  event: { key?: string | null; newValue?: string | null } | null | undefined,
+): boolean {
+  if (!event) return false;
+  if (event.key !== CROSS_TAB_STORAGE_KEY) return false;
+  if (event.newValue == null) return false;
+  try {
+    const parsed = JSON.parse(event.newValue) as unknown;
+    return isCrossTabInvalidationMessage(parsed);
+  } catch {
+    return false;
+  }
+}
diff --git a/frontend/src/app/core/services/auth.service.ts b/frontend/src/app/core/services/auth.service.ts
index 61fe496..58c591f 100644
--- a/frontend/src/app/core/services/auth.service.ts
+++ b/frontend/src/app/core/services/auth.service.ts
@@ -1,4 +1,4 @@
-import { Injectable, signal, computed, inject } from '@angular/core';
+import { Injectable, signal, computed, inject, DestroyRef } from '@angular/core';
 import { HttpClient, HttpErrorResponse } from '@angular/common/http';
 import { firstValueFrom } from 'rxjs';
 import {
@@ -7,6 +7,14 @@ import {
   clearStoredSession,
   StoredSession,
 } from './auth.session-storage';
+import {
+  CROSS_TAB_CHANNEL_NAME,
+  CROSS_TAB_STORAGE_KEY,
+  CrossTabInvalidationMessage,
+  encodeInvalidationMessage,
+  isCrossTabInvalidationMessage,
+  isStorageInvalidationEvent,
+} from './auth-session-events.pure';
 
 export interface CurrentUser {
   id: string;
@@ -78,9 +86,22 @@ export type ChangePasswordResult = ChangePasswordSuccess | ChangePasswordFailure
 @Injectable({ providedIn: 'root' })
 export class AuthService {
   private http: HttpClient;
+  private readonly destroyRef = inject(DestroyRef);
+
+  private readonly crossTabOrigin =
+    typeof crypto !== 'undefined' && typeof crypto.randomUUID === 'function'
+      ? crypto.randomUUID()
+      : `tab-${Math.random().toString(36).slice(2)}-${Date.now()}`;
+  private channel: BroadcastChannel | null = null;
+  private storageListener: ((ev: StorageEvent) => void) | null = null;
+  private suppressBroadcast = false;
+
+  private peerInvalidationListeners = new Set<(reason: 'peer-logout' | 'sse-unauthorized') => void>();
 
   constructor(http?: HttpClient) {
     this.http = http ?? inject(HttpClient);
+    this.installCrossTabListener();
+    this.destroyRef.onDestroy(() => this.teardownCrossTabListener());
   }
 
   private accessToken = signal<string | null>(null);
@@ -158,7 +179,7 @@ export class AuthService {
     } catch {
       // ignore network/auth errors; we still clear local state
     }
-    this.clear();
+    this.clearAndBroadcast();
   }
 
   async me(): Promise<MeResponse> {
@@ -204,10 +225,118 @@ export class AuthService {
     clearStoredSession(this.sessionStorage());
   }
 
+  clearAndBroadcast(): void {
+    this.clear();
+    if (this.suppressBroadcast) return;
+    const message = encodeInvalidationMessage(this.crossTabOrigin);
+    this.publishInvalidation(message);
+  }
+
+  handleSseUnauthorized(): void {
+    this.clearAndBroadcast();
+    this.notifyPeerInvalidation('sse-unauthorized');
+  }
+
+  onPeerInvalidation(cb: (reason: 'peer-logout' | 'sse-unauthorized') => void): () => void {
+    this.peerInvalidationListeners.add(cb);
+    return () => this.peerInvalidationListeners.delete(cb);
+  }
+
   getAccessToken(): string | null {
     return this.accessToken();
   }
 
+  private publishInvalidation(message: CrossTabInvalidationMessage): void {
+    if (this.channel) {
+      try {
+        this.channel.postMessage(message);
+      } catch {
+        // ignore serialization failures; the storage fallback will still fire
+      }
+    }
+    if (typeof window !== 'undefined' && window.localStorage) {
+      try {
+        window.localStorage.setItem(CROSS_TAB_STORAGE_KEY, JSON.stringify(message));
+      } catch {
+        // ignore quota / serialization errors
+      }
+    }
+  }
+
+  private installCrossTabListener(): void {
+    if (typeof window === 'undefined') return;
+    if (typeof BroadcastChannel !== 'undefined') {
+      try {
+        this.channel = new BroadcastChannel(CROSS_TAB_CHANNEL_NAME);
+        this.channel.addEventListener('message', this.onBroadcastMessage);
+      } catch {
+        this.channel = null;
+      }
+    }
+    this.storageListener = (ev: StorageEvent) => {
+      if (!isStorageInvalidationEvent(ev)) return;
+      this.handlePeerInvalidation(ev.newValue, 'peer-logout');
+    };
+    window.addEventListener('storage', this.storageListener);
+  }
+
+  private teardownCrossTabListener(): void {
+    if (this.channel) {
+      try {
+        this.channel.removeEventListener('message', this.onBroadcastMessage);
+        this.channel.close();
+      } catch {
+        // ignore
+      }
+      this.channel = null;
+    }
+    if (this.storageListener && typeof window !== 'undefined') {
+      try {
+        window.removeEventListener('storage', this.storageListener);
+      } catch {
+        // ignore
+      }
+      this.storageListener = null;
+    }
+    this.peerInvalidationListeners.clear();
+  }
+
+  private readonly onBroadcastMessage = (ev: MessageEvent<unknown>) => {
+    if (!isCrossTabInvalidationMessage(ev.data)) return;
+    if (ev.data.origin === this.crossTabOrigin) return;
+    this.handlePeerInvalidation(JSON.stringify(ev.data), 'peer-logout');
+  };
+
+  private handlePeerInvalidation(
+    raw: string | null,
+    reason: 'peer-logout' | 'sse-unauthorized',
+  ): void {
+    if (raw) {
+      try {
+        const parsed = JSON.parse(raw) as unknown;
+        if (!isCrossTabInvalidationMessage(parsed)) return;
+        if (parsed.origin === this.crossTabOrigin) return;
+      } catch {
+        return;
+      }
+    }
+    if (!this.isAuthenticated()) return;
+    this.suppressBroadcast = true;
+    this.clear();
+    this.suppressBroadcast = false;
+    this.notifyPeerInvalidation(reason);
+  }
+
+  private notifyPeerInvalidation(reason: 'peer-logout' | 'sse-unauthorized'): void {
+    for (const cb of this.peerInvalidationListeners) {
+      try {
+        cb(reason);
+      } catch {
+        // ignore listener errors
+      }
+    }
+  }
+
   private sessionStorage(): Storage {
     return typeof window !== 'undefined' ? window.sessionStorage : (undefined as unknown as Storage);
   }
diff --git a/frontend/src/app/core/services/authenticated-event-source.service.ts b/frontend/src/app/core/services/authenticated-event-source.service.ts
index e726a68..ec0a726 100644
--- a/frontend/src/app/core/services/authenticated-event-source.service.ts
+++ b/frontend/src/app/core/services/authenticated-event-source.service.ts
@@ -48,6 +48,11 @@ export class AuthenticatedEventSourceService {
       dispatch('error', new Event('error'));
     };
 
+    const fireUnauthorized = () => {
+      if (closed) return;
+      dispatch('unauthorized', new Event('unauthorized'));
+    };
+
     const start = async () => {
       try {
         const res = await fetch(url, {
@@ -56,6 +61,10 @@ export class AuthenticatedEventSourceService {
           credentials: 'include',
           signal: controller!.signal,
         });
+        if (res.status === 401 || res.status === 403) {
+          if (!closed) fireUnauthorized();
+          return;
+        }
         if (!res.ok || !res.body) {
           fireError();
           return;
diff --git a/frontend/src/app/core/services/event-status.pure.ts b/frontend/src/app/core/services/event-status.pure.ts
index a3cb986..65dbbcb 100644
--- a/frontend/src/app/core/services/event-status.pure.ts
+++ b/frontend/src/app/core/services/event-status.pure.ts
@@ -10,7 +10,10 @@ export interface EventStatePayload {
 }
 
 export interface EventSourceLike {
-  addEventListener(type: 'open' | 'message' | 'error', listener: (ev: MessageEvent | Event) => void): void;
+  addEventListener(
+    type: 'open' | 'message' | 'error' | 'unauthorized',
+    listener: (ev: MessageEvent | Event) => void,
+  ): void;
   close(): void;
 }
 
diff --git a/frontend/src/app/core/services/event-status.store.ts b/frontend/src/app/core/services/event-status.store.ts
index 379e59a..2a077b8 100644
--- a/frontend/src/app/core/services/event-status.store.ts
+++ b/frontend/src/app/core/services/event-status.store.ts
@@ -66,7 +66,7 @@ export class EventStatusStore {
     this.anchorDeltaMs.set(Date.now() - new Date(payload.serverNowUtc).getTime());
   }
 
-  start(createSource: () => EventSourceLike): void {
+  start(createSource: () => EventSourceLike, onUnauthorized?: () => void): void {
     this.stop();
     const src = createSource();
     this.source = src;
@@ -81,6 +81,15 @@ export class EventStatusStore {
         // ignore malformed frame
       }
     });
+    if (onUnauthorized) {
+      src.addEventListener('unauthorized', () => {
+        try {
+          onUnauthorized();
+        } catch {
+          // ignore
+        }
+      });
+    }
     if (!this.intervalId) {
       this.intervalId = setInterval(() => this.tick.update((v) => v + 1), 1000);
     }
diff --git a/frontend/src/app/features/home/home.component.ts b/frontend/src/app/features/home/home.component.ts
index 64a4d20..e5adc18 100644
--- a/frontend/src/app/features/home/home.component.ts
+++ b/frontend/src/app/features/home/home.component.ts
@@ -129,11 +129,21 @@ export class HomeComponent implements OnInit, OnDestroy {
   ngOnInit(): void {
     this.userStore.hydrateFromAuth();
     void this.userStore.loadMe();
-    this.eventStatus.start(() => this.authenticatedEventSource.open('/api/v1/events/status'));
+    this.eventStatus.start(
+      () => this.authenticatedEventSource.open('/api/v1/events/status'),
+      () => this.handleSessionInvalidated('sse-unauthorized'),
+    );
+    this.peerInvalidationUnsubscribe = this.auth.onPeerInvalidation((reason) =>
+      this.handleSessionInvalidated(reason),
+    );
   }
 
   ngOnDestroy(): void {
     this.eventStatus.stop();
+    if (this.peerInvalidationUnsubscribe) {
+      this.peerInvalidationUnsubscribe();
+      this.peerInvalidationUnsubscribe = null;
+    }
   }
 
   goHome(): void {
@@ -192,4 +202,23 @@ export class HomeComponent implements OnInit, OnDestroy {
     this.userStore.reset();
     await this.router.navigateByUrl('/login');
   }
+
+  private peerInvalidationUnsubscribe: (() => void) | null = null;
+  private navigatingToLogin = false;
+
+  private async handleSessionInvalidated(
+    _reason: 'peer-logout' | 'sse-unauthorized',
+  ): Promise<void> {
+    this.userStore.reset();
+    this.changePasswordOpen.set(false);
+    this.userMenuOpen.set(false);
+    if (this.navigatingToLogin) return;
+    if (this.router.url.startsWith('/login')) return;
+    this.navigatingToLogin = true;
+    try {
+      await this.router.navigateByUrl('/login');
+    } finally {
+      this.navigatingToLogin = false;
+    }
+  }
 }
diff --git a/tests/frontend/auth-session-events.spec.ts b/tests/frontend/auth-session-events.spec.ts
new file mode 100644
index 0000000..9c1fce9
--- /dev/null
+++ b/tests/frontend/auth-session-events.spec.ts
@@ -0,0 +1,93 @@
+import {
+  CROSS_TAB_CHANNEL_NAME,
+  CROSS_TAB_STORAGE_KEY,
+  CrossTabInvalidationMessage,
+  encodeInvalidationMessage,
+  isCrossTabInvalidationMessage,
+  isStorageInvalidationEvent,
+} from '../../frontend/src/app/core/services/auth-session-events.pure';
+
+describe('auth-session-events.pure', () => {
+  describe('encodeInvalidationMessage', () => {
+    it('produces a session-invalidated message with origin and timestamp', () => {
+      const before = Date.now();
+      const msg = encodeInvalidationMessage('tab-A');
+      const after = Date.now();
+      expect(msg.type).toBe('session-invalidated');
+      expect(msg.origin).toBe('tab-A');
+      expect(msg.ts).toBeGreaterThanOrEqual(before);
+      expect(msg.ts).toBeLessThanOrEqual(after);
+    });
+  });
+
+  describe('isCrossTabInvalidationMessage', () => {
+    it('accepts a properly shaped message', () => {
+      const msg: CrossTabInvalidationMessage = {
+        type: 'session-invalidated',
+        origin: 'x',
+        ts: 1,
+      };
+      expect(isCrossTabInvalidationMessage(msg)).toBe(true);
+    });
+
+    it('rejects non-objects', () => {
+      expect(isCrossTabInvalidationMessage(null)).toBe(false);
+      expect(isCrossTabInvalidationMessage(undefined)).toBe(false);
+      expect(isCrossTabInvalidationMessage('string')).toBe(false);
+      expect(isCrossTabInvalidationMessage(42)).toBe(false);
+    });
+
+    it('rejects objects with wrong type or missing fields', () => {
+      expect(isCrossTabInvalidationMessage({ type: 'other', origin: 'a', ts: 1 })).toBe(false);
+      expect(isCrossTabInvalidationMessage({ type: 'session-invalidated', origin: 1, ts: 1 })).toBe(
+        false,
+      );
+      expect(isCrossTabInvalidationMessage({ type: 'session-invalidated', origin: 'a' })).toBe(
+        false,
+      );
+      expect(
+        isCrossTabInvalidationMessage({ type: 'session-invalidated', origin: 'a', ts: 'now' }),
+      ).toBe(false);
+    });
+  });
+
+  describe('isStorageInvalidationEvent', () => {
+    it('accepts a well-formed storage event for the namespaced key', () => {
+      const ev = {
+        key: CROSS_TAB_STORAGE_KEY,
+        newValue: JSON.stringify(encodeInvalidationMessage('tab-X')),
+      };
+      expect(isStorageInvalidationEvent(ev)).toBe(true);
+    });
+
+    it('rejects events with a different key', () => {
+      const ev = {
+        key: 'other.key',
+        newValue: JSON.stringify(encodeInvalidationMessage('tab-X')),
+      };
+      expect(isStorageInvalidationEvent(ev)).toBe(false);
+    });
+
+    it('rejects events with no newValue (cleared key)', () => {
+      const ev = { key: CROSS_TAB_STORAGE_KEY, newValue: null };
+      expect(isStorageInvalidationEvent(ev)).toBe(false);
+    });
+
+    it('rejects malformed JSON payloads', () => {
+      const ev = { key: CROSS_TAB_STORAGE_KEY, newValue: 'not-json' };
+      expect(isStorageInvalidationEvent(ev)).toBe(false);
+    });
+
+    it('rejects nullish events', () => {
+      expect(isStorageInvalidationEvent(null)).toBe(false);
+      expect(isStorageInvalidationEvent(undefined)).toBe(false);
+    });
+  });
+
+  describe('constant exports', () => {
+    it('exposes a stable channel name and storage key', () => {
+      expect(CROSS_TAB_CHANNEL_NAME).toBe('hipctf.auth.v1');
+      expect(CROSS_TAB_STORAGE_KEY).toBe('hipctf.auth.invalidate.v1');
+    });
+  });
+});
diff --git a/tests/frontend/authenticated-event-source.spec.ts b/tests/frontend/authenticated-event-source.spec.ts
index b452867..2bd7b38 100644
--- a/tests/frontend/authenticated-event-source.spec.ts
+++ b/tests/frontend/authenticated-event-source.spec.ts
@@ -13,7 +13,10 @@ if (typeof (globalThis as any).TextDecoder === 'undefined') {
 }
 
 interface EventSourceLike {
-  addEventListener(type: 'open' | 'message' | 'error', listener: (ev: MessageEvent | Event) => void): void;
+  addEventListener(
+    type: 'open' | 'message' | 'error' | 'unauthorized',
+    listener: (ev: MessageEvent | Event) => void,
+  ): void;
   close(): void;
 }
 
@@ -33,6 +36,13 @@ function makeCaptureableFetch(frames: string[]) {
   return { fetchMock, get captured() { return captured; } };
 }
 
+function makeUnauthorizedFetch(status: number) {
+  const fetchMock = jest.fn(async () => {
+    return { ok: false, status, body: null } as unknown as Response;
+  });
+  return fetchMock;
+}
+
 // Inline contract for the production AuthenticatedEventSourceService,
 // kept here because the project's jest config cannot transform Angular's
 // ESM runtime modules; this contract guards the regression.
@@ -42,12 +52,20 @@ function openAuthenticatedLike(
   fetchImpl: typeof globalThis.fetch,
 ): EventSourceLike {
   let handler: ((ev: MessageEvent) => void) | null = null;
+  let unauthorizedHandler: ((ev: Event) => void) | null = null;
   void (async () => {
     const headers: Record<string, string> = { Accept: 'text/event-stream' };
     if (token) headers['Authorization'] = `Bearer ${token}`;
-    const res = await fetchImpl(url, { headers, credentials: 'include' });
-    if (!res || !(res as any).body) return;
-    const reader = ((res as any).body as ReadableStream<Uint8Array>).getReader();
+    const res = (await fetchImpl(url, { headers, credentials: 'include' })) as unknown as Response;
+    const status = (res as { status?: number }).status ?? 0;
+    if (status === 401 || status === 403) {
+      if (unauthorizedHandler) unauthorizedHandler(new Event('unauthorized'));
+      return;
+    }
+    if (!res || !(res as { body?: unknown }).body) return;
+    const reader = ((res as { body: ReadableStream<Uint8Array> }).body as ReadableStream<
+      Uint8Array
+    >).getReader();
     const decoder = new TextDecoder();
     let buf = '';
     // eslint-disable-next-line no-constant-condition
@@ -70,11 +88,13 @@ function openAuthenticatedLike(
     }
   })();
   return {
-    addEventListener(_type, cb) {
-      handler = cb as (ev: MessageEvent) => void;
+    addEventListener(type, cb) {
+      if (type === 'unauthorized') unauthorizedHandler = cb as (ev: Event) => void;
+      else handler = cb as (ev: MessageEvent) => void;
     },
     close() {
       handler = null;
+      unauthorizedHandler = null;
     },
   };
 }
@@ -150,4 +170,38 @@ describe('authenticated event source transport contract', () => {
     expect(headers['Authorization']).toBeUndefined();
     source.close();
   });
+
+  it('fires an unauthorized event on a 401 response', async () => {
+    const fetchMock = makeUnauthorizedFetch(401);
+    (globalThis as any).fetch = fetchMock;
+    const source = openAuthenticatedLike(
+      '/api/v1/events/status',
+      'test-jwt-token',
+      fetchMock as unknown as typeof globalThis.fetch,
+    );
+    const received: string[] = [];
+    source.addEventListener('unauthorized', (ev) => {
+      received.push(ev.type);
+    });
+    await new Promise((r) => setTimeout(r, 30));
+    expect(received).toEqual(['unauthorized']);
+    source.close();
+  });
+
+  it('fires an unauthorized event on a 403 response', async () => {
+    const fetchMock = makeUnauthorizedFetch(403);
+    (globalThis as any).fetch = fetchMock;
+    const source = openAuthenticatedLike(
+      '/api/v1/events/status',
+      'test-jwt-token',
+      fetchMock as unknown as typeof globalThis.fetch,
+    );
+    const received: string[] = [];
+    source.addEventListener('unauthorized', (ev) => {
+      received.push(ev.type);
+    });
+    await new Promise((r) => setTimeout(r, 30));
+    expect(received).toEqual(['unauthorized']);
+    source.close();
+  });
 });