diff --git a/archreview/plans/R2-08-ldap-historyread-async-plan.md.tasks.json b/archreview/plans/R2-08-ldap-historyread-async-plan.md.tasks.json
index b48a529d..d780299b 100644
--- a/archreview/plans/R2-08-ldap-historyread-async-plan.md.tasks.json
+++ b/archreview/plans/R2-08-ldap-historyread-async-plan.md.tasks.json
@@ -1,7 +1,7 @@
 {
   "planPath": "archreview/plans/R2-08-ldap-historyread-async-plan.md",
   "tasks": [
-    { "id": "R2-08-T1", "subject": "S2 stall-repro test (RED): slow LDAP backend must deny within AuthTimeout — fails on current code", "status": "pending", "blockedBy": [] },
+    { "id": "R2-08-T1", "subject": "S2 stall-repro test (RED): slow LDAP backend must deny within AuthTimeout — fails on current code", "status": "completed", "blockedBy": [] },
     { "id": "R2-08-T2", "subject": "LdapOptions: ConnectionTimeoutMs/AuthTimeoutMs/MaxConcurrentAuthentications/OutageFailureThreshold/OutageCooldownSeconds + ToLibraryOptions projection + validator rules", "status": "pending", "blockedBy": [] },
     { "id": "R2-08-T3", "subject": "LdapAuthResult.IsSystemFailure seam + OtOpcUaLdapAuthService.Adapt mapping (ServiceAccountBindFailed => system-side)", "status": "pending", "blockedBy": [] },
     { "id": "R2-08-T4", "subject": "LdapOpcUaUserAuthenticator: WaitAsync wall-clock bound + SemaphoreSlim concurrency cap with release-on-core-completion (turns T1 green)", "status": "pending", "blockedBy": ["R2-08-T1", "R2-08-T2"] },
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.Host.IntegrationTests/LdapAuthResilienceTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.Host.IntegrationTests/LdapAuthResilienceTests.cs
new file mode 100644
index 00000000..d43fafd4
--- /dev/null
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.Host.IntegrationTests/LdapAuthResilienceTests.cs
@@ -0,0 +1,104 @@
+using System.Diagnostics;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging.Abstractions;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.Auth.Abstractions.Roles;
+using ZB.MOM.WW.OtOpcUa.Host.OpcUa;
+using ZB.MOM.WW.OtOpcUa.Security.Ldap;
+
+namespace ZB.MOM.WW.OtOpcUa.Host.IntegrationTests;
+
+/// <summary>
+/// Resilience guard for <see cref="LdapOpcUaUserAuthenticator"/> (arch-review 03/S2). The OPC UA SDK
+/// raises the impersonation callback synchronously under a <c>SessionManager</c>-wide event lock, so a
+/// slow / hung LDAP bind inside it does not merely stall one SDK thread — it serializes EVERY session
+/// activation server-wide. These tests prove the authenticator enforces a hard wall-clock bound,
+/// bounded in-flight concurrency, and a directory-outage circuit at its own boundary (the SDK callback
+/// being irreducibly synchronous), all fail-closed. No real LDAP server is used — a delaying fake
+/// reproduces the outage shape offline.
+/// </summary>
+public sealed class LdapAuthResilienceTests
+{
+    /// <summary>
+    /// RED repro (03/S2): a backend that takes 5 s must NOT hold the caller for 5 s — the authenticator's
+    /// wall-clock bound denies (fail-closed) well before then. On current code (no bound) this fails: the
+    /// call returns Allow after the full 5 s.
+    /// </summary>
+    [Fact]
+    public async Task Authenticate_slow_backend_denies_within_AuthTimeout()
+    {
+        var ldap = new DelayingFakeLdap(
+            TimeSpan.FromSeconds(5),
+            new LdapAuthResult(true, "Alice", "alice", new[] { "configeditor" }, Array.Empty<string>(), null));
+        var mapper = new FakeMapper(g => g.ToArray());
+        var sut = new LdapOpcUaUserAuthenticator(
+            ldap,
+            ScopeFactoryWith(mapper),
+            NullLogger<LdapOpcUaUserAuthenticator>.Instance);
+
+        var sw = Stopwatch.StartNew();
+        var result = await sut
+            .AuthenticateUserNameAsync("alice", "secret", CancellationToken.None)
+            .WaitAsync(TimeSpan.FromSeconds(10), CancellationToken.None);
+        sw.Stop();
+
+        result.Success.ShouldBeFalse();
+        result.Error.ShouldNotBeNull();
+        result.Error!.ShouldContain("timed out");
+        sw.Elapsed.ShouldBeLessThan(TimeSpan.FromSeconds(1.5));
+    }
+
+    /// <summary>Builds an IServiceScopeFactory whose scopes resolve the supplied mapper.</summary>
+    private static IServiceScopeFactory ScopeFactoryWith(IGroupRoleMapper<string> mapper)
+    {
+        var services = new ServiceCollection();
+        services.AddScoped(_ => mapper);
+        return services.BuildServiceProvider().GetRequiredService<IServiceScopeFactory>();
+    }
+
+    /// <summary>
+    /// A fake <see cref="ILdapAuthService"/> that awaits a configurable delay (observing the token) before
+    /// returning a fixed result — the offline stand-in for a slow / hung directory. Counts invocations so
+    /// tests can assert the outage circuit denies WITHOUT reaching the backend.
+    /// </summary>
+    private sealed class DelayingFakeLdap : ILdapAuthService
+    {
+        private readonly TimeSpan _delay;
+        private readonly LdapAuthResult _then;
+        private int _calls;
+
+        /// <summary>Initializes the fake with a per-call delay and the result to return afterwards.</summary>
+        /// <param name="delay">How long each authenticate call blocks before returning.</param>
+        /// <param name="then">The result returned once the delay elapses.</param>
+        public DelayingFakeLdap(TimeSpan delay, LdapAuthResult then)
+        {
+            _delay = delay;
+            _then = then;
+        }
+
+        /// <summary>The number of times the backend was actually invoked.</summary>
+        public int Calls => Volatile.Read(ref _calls);
+
+        /// <summary>Awaits the configured delay, then returns the canned result.</summary>
+        /// <param name="username">The username (ignored).</param>
+        /// <param name="password">The password (ignored).</param>
+        /// <param name="ct">Cancellation token, observed by the delay.</param>
+        public async Task<LdapAuthResult> AuthenticateAsync(string username, string password, CancellationToken ct = default)
+        {
+            Interlocked.Increment(ref _calls);
+            await Task.Delay(_delay, ct).ConfigureAwait(false);
+            return _then;
+        }
+    }
+
+    /// <summary>Test group→role mapper driven by a delegate over the supplied groups.</summary>
+    private sealed class FakeMapper(Func<IReadOnlyList<string>, IReadOnlyList<string>> map) : IGroupRoleMapper<string>
+    {
+        /// <summary>Maps groups to roles via the configured delegate; Scope is always null.</summary>
+        /// <param name="groups">The LDAP groups to map.</param>
+        /// <param name="ct">The cancellation token.</param>
+        public Task<GroupRoleMapping<string>> MapAsync(IReadOnlyList<string> groups, CancellationToken ct)
+            => Task.FromResult(new GroupRoleMapping<string>(map(groups), Scope: null));
+    }
+}