diff --git a/src/ZB.MOM.WW.ScadaBridge.DeploymentManager/DeploymentService.cs b/src/ZB.MOM.WW.ScadaBridge.DeploymentManager/DeploymentService.cs
index a7fbfa62..3e405507 100644
--- a/src/ZB.MOM.WW.ScadaBridge.DeploymentManager/DeploymentService.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.DeploymentManager/DeploymentService.cs
@@ -326,8 +326,11 @@ public class DeploymentService
                     forceEnabledState: true, cancellationToken);
             }
 
-            // Audit log
-            await _auditService.LogAsync(user, "Deploy", "Instance", instanceId.ToString(),
+            // Audit log. Best-effort and post-terminal: the deployment record's
+            // status is already committed above, so a failed audit write must NOT
+            // fall through to the outer catch and flip a committed Success back to
+            // Failed (audit is best-effort — the action's own result is authoritative).
+            await TryLogAuditAsync(user, "Deploy", "Instance", instanceId.ToString(),
                 instance.UniqueName, new { DeploymentId = deploymentId, Status = record.Status.ToString() },
                 cancellationToken);
 
@@ -458,7 +461,7 @@ public class DeploymentService
             await _repository.SaveChangesAsync(cancellationToken);
         }
 
-        await _auditService.LogAsync(user, "Disable", "Instance", instanceId.ToString(),
+        await TryLogAuditAsync(user, "Disable", "Instance", instanceId.ToString(),
             instance.UniqueName, new { CommandId = commandId, response.Success },
             cancellationToken);
 
@@ -522,7 +525,7 @@ public class DeploymentService
             await _repository.SaveChangesAsync(cancellationToken);
         }
 
-        await _auditService.LogAsync(user, "Enable", "Instance", instanceId.ToString(),
+        await TryLogAuditAsync(user, "Enable", "Instance", instanceId.ToString(),
             instance.UniqueName, new { CommandId = commandId, response.Success },
             cancellationToken);
 
@@ -609,7 +612,7 @@ public class DeploymentService
                     "removed -- the central record is now orphaned and must be reconciled manually",
                     instance.UniqueName);
 
-                await _auditService.LogAsync(user, "DeleteOrphaned", "Instance", instanceId.ToString(),
+                await TryLogAuditAsync(user, "DeleteOrphaned", "Instance", instanceId.ToString(),
                     instance.UniqueName, new { CommandId = commandId, Error = ex.Message },
                     CancellationToken.None);
 
@@ -619,7 +622,7 @@ public class DeploymentService
             }
         }
 
-        await _auditService.LogAsync(user, "Delete", "Instance", instanceId.ToString(),
+        await TryLogAuditAsync(user, "Delete", "Instance", instanceId.ToString(),
             instance.UniqueName, new { CommandId = commandId, response.Success },
             cancellationToken);
 
@@ -1035,6 +1038,37 @@ public class DeploymentService
     /// <param name="instanceUniqueName">The instance unique name used as the audit target name.</param>
     /// <param name="commandId">The lifecycle command's correlation id, so the audit entry can be matched to logs.</param>
     /// <param name="timeoutException">The captured <see cref="TimeoutException"/> or <see cref="OperationCanceledException"/>.</param>
+    /// <summary>
+    /// Best-effort audit write for a post-terminal-status action. By the time this
+    /// runs, the deployment/lifecycle action has already committed its authoritative
+    /// result; a failed audit write must be logged for operator reconciliation but
+    /// must NEVER surface to the caller or flip the committed status — "audit-write
+    /// failure NEVER aborts the user-facing action" (Centralized Audit Log design).
+    /// Any exception is swallowed and logged at Warning.
+    /// </summary>
+    private async Task TryLogAuditAsync(
+        string user,
+        string action,
+        string entityType,
+        string entityId,
+        string entityName,
+        object? afterState,
+        CancellationToken cancellationToken)
+    {
+        try
+        {
+            await _auditService.LogAsync(
+                user, action, entityType, entityId, entityName, afterState, cancellationToken);
+        }
+        catch (Exception auditEx)
+        {
+            _logger.LogWarning(auditEx,
+                "Failed to write {Action} audit entry for {EntityType} {EntityName} -- the action " +
+                "itself succeeded and its committed status is authoritative; audit is best-effort",
+                action, entityType, entityName);
+        }
+    }
+
     private async Task TryLogLifecycleTimeoutAsync(
         string user,
         string action,
diff --git a/tests/ZB.MOM.WW.ScadaBridge.DeploymentManager.Tests/DeploymentServiceTests.cs b/tests/ZB.MOM.WW.ScadaBridge.DeploymentManager.Tests/DeploymentServiceTests.cs
index e8581351..ddcb4801 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.DeploymentManager.Tests/DeploymentServiceTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.DeploymentManager.Tests/DeploymentServiceTests.cs
@@ -878,6 +878,36 @@ public class DeploymentServiceTests : TestKit
             Arg.Any<object>(), Arg.Any<CancellationToken>());
     }
 
+    [Fact]
+    public async Task DeployInstanceAsync_DeployAuditWriteThrows_KeepsCommittedSuccess()
+    {
+        // #05-T17: the post-success "Deploy" audit write is best-effort. If it
+        // throws, the already-committed Success record must NOT be flipped to
+        // Failed by the outer catch — "audit-write failure NEVER aborts the
+        // user-facing action".
+        var instance = new Instance("AuditFaultInst") { Id = 52, SiteId = 1, State = InstanceState.NotDeployed };
+        _repo.GetInstanceByIdAsync(52, Arg.Any<CancellationToken>()).Returns(instance);
+        SetupValidPipeline(52, "AuditFaultInst", "sha256:target");
+        _repo.GetCurrentDeploymentStatusAsync(52, Arg.Any<CancellationToken>())
+            .Returns((DeploymentRecord?)null);
+
+        // The Deploy audit LogAsync faults.
+        _audit.When(a => a.LogAsync(
+                Arg.Any<string>(), "Deploy", Arg.Any<string>(), Arg.Any<string>(),
+                Arg.Any<string>(), Arg.Any<object>(), Arg.Any<CancellationToken>()))
+            .Do(_ => throw new InvalidOperationException("audit pipeline down"));
+
+        var counters = new ReconcileProbeCounters();
+        var commActor = Sys.ActorOf(Props.Create(() =>
+            new ReconcileProbeActor(counters, siteHash: "sha256:target", failQuery: false)));
+        var service = CreateServiceWithCommActor(commActor);
+
+        var result = await service.DeployInstanceAsync(52, "admin");
+
+        Assert.True(result.IsSuccess);
+        Assert.Equal(DeploymentStatus.Success, result.Value.Status);
+    }
+
     // ── Telemetry follow-on: scadabridge.deployments.applied on deploy success ──
 
     [Fact]