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 d5df7283..08933cfd 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
@@ -3,7 +3,7 @@
   "tasks": [
     { "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": "completed", "blockedBy": [] },
-    { "id": "R2-08-T3", "subject": "LdapAuthResult.IsSystemFailure seam + OtOpcUaLdapAuthService.Adapt mapping (ServiceAccountBindFailed => system-side)", "status": "pending", "blockedBy": [] },
+    { "id": "R2-08-T3", "subject": "LdapAuthResult.IsSystemFailure seam + OtOpcUaLdapAuthService.Adapt mapping (ServiceAccountBindFailed => system-side)", "status": "completed", "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"] },
     { "id": "R2-08-T5", "subject": "Directory-outage circuit: fail-fast deny after N consecutive system-side failures, half-open after cooldown", "status": "pending", "blockedBy": ["R2-08-T3", "R2-08-T4"] },
     { "id": "R2-08-T6", "subject": "Outage-sim integration test (real library, unroutable host, via internal HandleImpersonation) + SDK m_eventLock contract doc + docs/security.md", "status": "pending", "blockedBy": ["R2-08-T4"] },
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.Security/Ldap/LdapAuthResult.cs b/src/Server/ZB.MOM.WW.OtOpcUa.Security/Ldap/LdapAuthResult.cs
index 4ca801e6..a91cae04 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.Security/Ldap/LdapAuthResult.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.Security/Ldap/LdapAuthResult.cs
@@ -7,4 +7,15 @@ public sealed record LdapAuthResult(
     string? Username,
     IReadOnlyList<string> Groups,
     IReadOnlyList<string> Roles,
-    string? Error);
+    string? Error)
+{
+    /// <summary>
+    ///     <c>true</c> when this failure is a SYSTEM-side directory fault (the directory is unreachable or
+    ///     the service account is misconfigured) rather than a user-credential deny. Feeds the OPC UA
+    ///     data-plane authenticator's outage circuit (03/S2): a run of consecutive system-side failures
+    ///     opens the circuit and fails fast, whereas user-side denies never trip it. Always <c>false</c>
+    ///     on success and on user-side denies; set only on the delegated real path for the library's
+    ///     directory-unreachable bucket.
+    /// </summary>
+    public bool IsSystemFailure { get; init; }
+}
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.Security/Ldap/OtOpcUaLdapAuthService.cs b/src/Server/ZB.MOM.WW.OtOpcUa.Security/Ldap/OtOpcUaLdapAuthService.cs
index 373ee4f4..6ddf8bb5 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.Security/Ldap/OtOpcUaLdapAuthService.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.Security/Ldap/OtOpcUaLdapAuthService.cs
@@ -113,7 +113,13 @@ public sealed class OtOpcUaLdapAuthService : ILdapAuthService
         if (result.Succeeded)
             return new(true, result.DisplayName, result.Username, result.Groups, [], null);
 
-        return new(false, null, username, [], [], FailureToError(result.Failure));
+        // ServiceAccountBindFailed is the library's directory-unreachable / service-account-misconfigured
+        // bucket (its enum has no dedicated DirectoryUnavailable) — flag it as system-side so the OPC UA
+        // authenticator's outage circuit can distinguish an outage from a user-credential deny (03/S2).
+        return new(false, null, username, [], [], FailureToError(result.Failure))
+        {
+            IsSystemFailure = result.Failure is LdapAuthFailure.ServiceAccountBindFailed,
+        };
     }
 
     /// <summary>Folds a structured library failure code into the app's user-facing error text.</summary>
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.Security.Tests/OtOpcUaLdapAuthServiceTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.Security.Tests/OtOpcUaLdapAuthServiceTests.cs
index d0b9354b..3146ba8b 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.Security.Tests/OtOpcUaLdapAuthServiceTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.Security.Tests/OtOpcUaLdapAuthServiceTests.cs
@@ -121,6 +121,56 @@ public sealed class OtOpcUaLdapAuthServiceTests
         inner.Called.ShouldBeFalse();
     }
 
+    /// <summary>A system-side library failure (<c>ServiceAccountBindFailed</c> — the directory-unreachable
+    /// bucket) adapts to <c>IsSystemFailure == true</c> so the OPC UA authenticator's outage circuit can
+    /// distinguish it from a user-credential deny (03/S2).</summary>
+    [Fact]
+    public async Task ServiceAccountBindFailed_adapts_to_IsSystemFailure_true()
+    {
+        var inner = new RecordingLibService(LibLdapAuthResult.Fail(LdapAuthFailure.ServiceAccountBindFailed));
+        var sut = Build(
+            new LdapOptions { Enabled = true, DevStubMode = false, Transport = LdapTransport.Ldaps },
+            inner);
+
+        var result = await sut.AuthenticateAsync("alice", "secret", CancellationToken.None);
+
+        result.Success.ShouldBeFalse();
+        result.IsSystemFailure.ShouldBeTrue();
+    }
+
+    /// <summary>User-side library failures and success adapt to <c>IsSystemFailure == false</c> — they must
+    /// NOT trip the outage circuit (03/S2).</summary>
+    [Theory]
+    [InlineData(LdapAuthFailure.BadCredentials)]
+    [InlineData(LdapAuthFailure.UserNotFound)]
+    public async Task User_side_failures_adapt_to_IsSystemFailure_false(LdapAuthFailure failure)
+    {
+        var inner = new RecordingLibService(LibLdapAuthResult.Fail(failure));
+        var sut = Build(
+            new LdapOptions { Enabled = true, DevStubMode = false, Transport = LdapTransport.Ldaps },
+            inner);
+
+        var result = await sut.AuthenticateAsync("alice", "wrong", CancellationToken.None);
+
+        result.Success.ShouldBeFalse();
+        result.IsSystemFailure.ShouldBeFalse();
+    }
+
+    /// <summary>A successful bind is never a system failure.</summary>
+    [Fact]
+    public async Task Success_is_not_a_system_failure()
+    {
+        var inner = new RecordingLibService(LibLdapAuthResult.Success("alice", "Alice", new[] { "ReadOnly" }));
+        var sut = Build(
+            new LdapOptions { Enabled = true, DevStubMode = false, Transport = LdapTransport.Ldaps },
+            inner);
+
+        var result = await sut.AuthenticateAsync("alice", "secret", CancellationToken.None);
+
+        result.Success.ShouldBeTrue();
+        result.IsSystemFailure.ShouldBeFalse();
+    }
+
     /// <summary>Records whether the library service was invoked and returns a canned result.</summary>
     private sealed class RecordingLibService(LibLdapAuthResult result) : LibILdapAuthService
     {