diff --git a/frontend/electron/main.ts b/frontend/electron/main.ts
index ec1df1c..fed6c7f 100644
--- a/frontend/electron/main.ts
+++ b/frontend/electron/main.ts
@@ -524,13 +524,40 @@ ipcMain.handle('open-steam-app-login', async () => {
 });
 
 ipcMain.handle('open-steam-login', async (event, expectedSteamId: string) => {
-  const loginSession = session.fromPartition('persist:steam-login');
-  // Removed: automatic clearStorageData to allow cookie persistence
+  // Use a unique partition per account to prevent session bleeding
+  const partitionId = expectedSteamId ? `persist:steam-login-${expectedSteamId}` : 'persist:steam-login-new';
+  const loginSession = session.fromPartition(partitionId);
+
+  // If we have an existing cookie string for this account, pre-inject it
+  if (expectedSteamId) {
+    const accounts = store.get('accounts') as Account[];
+    const account = accounts.find(a => a.steamId === expectedSteamId);
+    if (account?.steamLoginSecure) {
+      console.log(`[Auth] Pre-injecting existing cookies for ${account.personaName}...`);
+      const cookiePairs = account.steamLoginSecure.split(';').map(c => c.trim());
+      for (const pair of cookiePairs) {
+        const [name, value] = pair.split('=');
+        if (name && value) {
+          try {
+            await loginSession.cookies.set({
+              url: 'https://steamcommunity.com',
+              domain: 'steamcommunity.com',
+              name: name,
+              value: value,
+              path: '/',
+              secure: true,
+              httpOnly: name.includes('Secure')
+            });
+          } catch (e) {}
+        }
+      }
+    }
+  }
 
   return new Promise<boolean>((resolve) => {
     const loginWindow = new BrowserWindow({
       width: 800, height: 700, parent: mainWindow || undefined, modal: true, title: 'Login to Steam',
-      webPreferences: { nodeIntegration: false, contextIsolation: true, partition: 'persist:steam-login' }
+      webPreferences: { nodeIntegration: false, contextIsolation: true, partition: partitionId }
     });
     loginWindow.loadURL('https://steamcommunity.com/login/home/?goto=my/gcpd/730');
     const checkCookie = setInterval(async () => {