diff --git a/apps/stalker-mock-server/src/app/auth-store.ts b/apps/stalker-mock-server/src/app/auth-store.ts
index a69b5d7db..c32486f5f 100644
--- a/apps/stalker-mock-server/src/app/auth-store.ts
+++ b/apps/stalker-mock-server/src/app/auth-store.ts
@@ -201,7 +201,11 @@ export function invalidateSession(mac: string): void {
     session.pendingToken = undefined;
 }
 
-export function resetAuthState(): void {
+export function resetAuthState(mac?: string): void {
+    if (mac) {
+        sessions.delete(mac.toLowerCase());
+        return;
+    }
     sessions.clear();
     tokenCounter = 0;
 }
diff --git a/apps/stalker-mock-server/src/app/data-store.ts b/apps/stalker-mock-server/src/app/data-store.ts
index 52a16a756..4aca56f4f 100644
--- a/apps/stalker-mock-server/src/app/data-store.ts
+++ b/apps/stalker-mock-server/src/app/data-store.ts
@@ -44,6 +44,17 @@ export function resetFavorites(mac: string): void {
     favoritesStore.delete(mac.toLowerCase());
 }
 
+/**
+ * Reset everything cached for one MAC. Preferred over `resetAll()` in tests:
+ * mock state is per-MAC, so a scoped reset cannot disturb a spec that runs
+ * concurrently against a different MAC.
+ */
+export function resetMac(mac: string): void {
+    const key = mac.toLowerCase();
+    portalCache.delete(key);
+    favoritesStore.delete(key);
+}
+
 /** Reset all cached data (exposed via /reset endpoint). */
 export function resetAll(): void {
     portalCache.clear();
diff --git a/apps/stalker-mock-server/src/app/handlers/get-events.handler.ts b/apps/stalker-mock-server/src/app/handlers/get-events.handler.ts
index 9132ab64a..32cc4c37a 100644
--- a/apps/stalker-mock-server/src/app/handlers/get-events.handler.ts
+++ b/apps/stalker-mock-server/src/app/handlers/get-events.handler.ts
@@ -35,6 +35,10 @@ export function getWatchdogPings(
     return watchdogPings.get(mac.toLowerCase());
 }
 
-export function resetWatchdogPings(): void {
+export function resetWatchdogPings(mac?: string): void {
+    if (mac) {
+        watchdogPings.delete(mac.toLowerCase());
+        return;
+    }
     watchdogPings.clear();
 }
diff --git a/apps/stalker-mock-server/src/main.ts b/apps/stalker-mock-server/src/main.ts
index 93b2876dc..121e26354 100644
--- a/apps/stalker-mock-server/src/main.ts
+++ b/apps/stalker-mock-server/src/main.ts
@@ -6,7 +6,7 @@ import portalRouter, { createPortalRouter } from './app/routes/portal.route.js';
 import dispatchPortalAction from './app/routes/dispatch.js';
 import { invalidateSession, resetAuthState } from './app/auth-store.js';
 import { resetWatchdogPings } from './app/handlers/get-events.handler.js';
-import { resetAll } from './app/data-store.js';
+import { resetAll, resetMac } from './app/data-store.js';
 import { SCENARIOS } from './app/scenarios.js';
 import {
     buildRequestOrigin,
@@ -173,12 +173,34 @@ app.get('/health', (_req: Request, res: Response) => {
     res.json({ status: 'ok', timestamp: new Date().toISOString() });
 });
 
-// Reset all in-memory data (useful between Playwright test runs)
-app.post('/reset', (_req: Request, res: Response) => {
-    resetAll();
-    resetAuthState();
-    resetWatchdogPings();
-    res.json({ status: 'reset', timestamp: new Date().toISOString() });
+/**
+ * Reset in-memory state between test runs.
+ *
+ * `?macAddress=<mac>` scopes the reset to that MAC and is what specs should
+ * use: mock state is per-MAC, so a scoped reset cannot wipe the session of a
+ * spec file running concurrently in another Playwright worker. Without the
+ * parameter everything is cleared, which is only safe when nothing else is
+ * talking to this server.
+ */
+app.post('/reset', (req: Request, res: Response) => {
+    const macParam = req.query['macAddress'];
+    const mac = typeof macParam === 'string' ? macParam : undefined;
+
+    if (mac) {
+        resetMac(mac);
+        resetAuthState(mac);
+        resetWatchdogPings(mac);
+    } else {
+        resetAll();
+        resetAuthState();
+        resetWatchdogPings();
+    }
+
+    res.json({
+        status: 'reset',
+        ...(mac ? { mac } : {}),
+        timestamp: new Date().toISOString(),
+    });
 });
 
 /**
diff --git a/apps/web-e2e/src/self-hosted.e2e.ts b/apps/web-e2e/src/self-hosted.e2e.ts
index b00a0b5f1..782ef4ce7 100644
--- a/apps/web-e2e/src/self-hosted.e2e.ts
+++ b/apps/web-e2e/src/self-hosted.e2e.ts
@@ -102,7 +102,13 @@ function expectRequestsUseTargetId(requests: string[], path: string): void {
 
 test.beforeEach(async ({ page, request }) => {
     await request.post(`${XTREAM_MOCK_SERVER}/reset`);
-    await request.post(`${STALKER_MOCK_SERVER}/reset`);
+    // Scope the Stalker reset to the MAC this file uses: a global reset would
+    // wipe the sessions of stalker.e2e.ts running in a parallel worker.
+    await request.post(
+        `${STALKER_MOCK_SERVER}/reset?macAddress=${encodeURIComponent(
+            DEFAULT_MAC
+        )}`
+    );
     await installRuntimeConfig(page);
     await page.goto('/');
 });
diff --git a/apps/web-e2e/src/stalker.e2e.ts b/apps/web-e2e/src/stalker.e2e.ts
index 0600813de..2fbb6196d 100644
--- a/apps/web-e2e/src/stalker.e2e.ts
+++ b/apps/web-e2e/src/stalker.e2e.ts
@@ -106,12 +106,38 @@ async function interceptStalkerRequests(page: Page): Promise<void> {
     });
 }
 
+/** Every MAC this file touches; each is reset individually (see below). */
+const OWNED_MACS = [
+    DEFAULT_MAC,
+    MINIMAL_MAC,
+    EMBEDDED_SERIES_MAC,
+    LEGACY_PAGINATION_MAC,
+    AUTH_FLOW_MAC,
+    AUTH_REAUTH_MAC,
+    AUTH_REJECTED_MAC,
+];
+
+/**
+ * Reset only the MACs this file owns. Mock state is per-MAC and other spec
+ * files (self-hosted.e2e.ts) talk to the same server from a parallel worker,
+ * so a global reset here would wipe their sessions mid-test — and theirs
+ * would wipe ours.
+ */
 async function resetMockServer(request: APIRequestContext): Promise<void> {
+    await Promise.all(OWNED_MACS.map((mac) => resetMockServerMac(request, mac)));
+}
+
+async function resetMockServerMac(
+    request: APIRequestContext,
+    mac: string
+): Promise<void> {
     let lastError: unknown;
 
     for (let attempt = 0; attempt < 3; attempt += 1) {
         try {
-            const response = await request.post(`${MOCK_SERVER}/reset`);
+            const response = await request.post(
+                `${MOCK_SERVER}/reset?macAddress=${encodeURIComponent(mac)}`
+            );
             if (response.ok()) {
                 return;
             }
@@ -630,9 +656,12 @@ test('@stalker mock server reset clears cached state', async ({ request }) => {
     );
     expect(before.ok()).toBeTruthy();
 
-    // Reset
-    const reset = await request.post(`${MOCK_SERVER}/reset`);
+    // Scoped reset — a global one would clear MACs owned by parallel specs.
+    const reset = await request.post(
+        `${MOCK_SERVER}/reset?macAddress=${encodeURIComponent(DEFAULT_MAC)}`
+    );
     expect(reset.ok()).toBeTruthy();
+    expect((await reset.json()).mac).toBe(DEFAULT_MAC);
 
     // Data is regenerated identically (deterministic seed)
     const after = await request.get(