diff --git a/NEW/tests/JdeScoping.Api.IntegrationTests/ClientIntegration/ClientIntegrationCollection.cs b/NEW/tests/JdeScoping.Api.IntegrationTests/ClientIntegration/ClientIntegrationCollection.cs
new file mode 100644
index 0000000..60a5f14
--- /dev/null
+++ b/NEW/tests/JdeScoping.Api.IntegrationTests/ClientIntegration/ClientIntegrationCollection.cs
@@ -0,0 +1,10 @@
+namespace JdeScoping.Api.IntegrationTests.ClientIntegration;
+
+/// <summary>
+/// Collection definition for client integration tests.
+/// Prevents parallel execution to avoid auth state conflicts.
+/// </summary>
+[CollectionDefinition("ClientIntegration")]
+public class ClientIntegrationCollection : ICollectionFixture<TestWebApplicationFactory>
+{
+}
diff --git a/NEW/tests/JdeScoping.Api.IntegrationTests/ClientIntegration/ClientIntegrationTestBase.cs b/NEW/tests/JdeScoping.Api.IntegrationTests/ClientIntegration/ClientIntegrationTestBase.cs
new file mode 100644
index 0000000..1851695
--- /dev/null
+++ b/NEW/tests/JdeScoping.Api.IntegrationTests/ClientIntegration/ClientIntegrationTestBase.cs
@@ -0,0 +1,77 @@
+using System.Security.Cryptography;
+using System.Text;
+using System.Text.Json;
+using JdeScoping.Client.Services;
+using JdeScoping.Core.Models.Auth;
+using Microsoft.AspNetCore.Mvc.Testing;
+
+namespace JdeScoping.Api.IntegrationTests.ClientIntegration;
+
+/// <summary>
+/// Base class for API client integration tests.
+/// Provides shared HttpClient with cookie handling for auth state.
+/// </summary>
+[Collection("ClientIntegration")]
+public abstract class ClientIntegrationTestBase : IClassFixture<TestWebApplicationFactory>
+{
+    protected readonly TestWebApplicationFactory Factory;
+    protected readonly HttpClient SharedClient;
+
+    // API clients share the authenticated HttpClient
+    protected readonly SearchApiClient SearchClient;
+    protected readonly LookupApiClient LookupClient;
+    protected readonly AuthApiClient AuthClient;
+    protected readonly FileApiClient FileClient;
+
+    protected ClientIntegrationTestBase(TestWebApplicationFactory factory)
+    {
+        Factory = factory;
+        SharedClient = factory.CreateClient(new WebApplicationFactoryClientOptions
+        {
+            HandleCookies = true,
+            AllowAutoRedirect = false
+        });
+
+        // All clients share the same HttpClient (cookie container)
+        SearchClient = new SearchApiClient(SharedClient);
+        LookupClient = new LookupApiClient(SharedClient);
+        FileClient = new FileApiClient(SharedClient);
+        AuthClient = new AuthApiClient(SharedClient);
+    }
+
+    /// <summary>
+    /// Performs login with encrypted credentials.
+    /// </summary>
+    protected async Task LoginAsync(string username = "testuser", string password = "testpass")
+    {
+        // Step 1: Get public key
+        var publicKeyResult = await AuthClient.GetPublicKeyAsync();
+        if (!publicKeyResult.IsSuccess)
+            throw new Exception("Failed to get public key");
+
+        // Step 2: Encrypt credentials
+        var loginModel = new LoginModel { Username = username, Password = password };
+        var json = JsonSerializer.Serialize(loginModel);
+        var plaintext = Encoding.UTF8.GetBytes(json);
+
+        using var rsa = RSA.Create();
+        rsa.ImportFromPem(publicKeyResult.Value.PublicKeyPem);
+        var ciphertext = rsa.Encrypt(plaintext, RSAEncryptionPadding.OaepSHA256);
+
+        // Step 3: Login
+        var encryptedRequest = new EncryptedLoginRequest(Convert.ToBase64String(ciphertext));
+        var loginResult = await AuthClient.LoginAsync(encryptedRequest);
+
+        if (!loginResult.IsSuccess || !loginResult.Value.Success)
+            throw new Exception($"Login failed: {loginResult.Value?.ErrorMessage ?? "Unknown error"}");
+    }
+
+    /// <summary>
+    /// Creates a fresh HttpClient without cookies for testing unauthorized scenarios.
+    /// </summary>
+    protected HttpClient CreateFreshClient() => Factory.CreateClient(new WebApplicationFactoryClientOptions
+    {
+        HandleCookies = false,
+        AllowAutoRedirect = false
+    });
+}