Add unit tests for PackRunAttestation and SealedInstallEnforcer

- Implement comprehensive tests for PackRunAttestationService, covering attestation generation, verification, and event emission.
- Add tests for SealedInstallEnforcer to validate sealed install requirements and enforcement logic.
- Introduce a MonacoLoaderService stub for testing purposes to prevent Monaco workers/styles from loading during Karma runs.

src/Scheduler/__Libraries/StellaOps.Scheduler.Queue/SchedulerQueueContracts.cs

@@ -1,11 +1,10 @@
 using System;
-using System.Collections.Generic;
+using System.Collections.Generic;
 using System.Collections.ObjectModel;
 using System.Text.Json.Serialization;
 using System.Threading;
 using System.Threading.Tasks;
 using StellaOps.Scheduler.Models;
-using StellaOps.Scheduler.Worker.Planning;
 
 namespace StellaOps.Scheduler.Queue;
 
@@ -156,9 +155,9 @@ public sealed class RunnerSegmentQueueMessage
         public static readonly IReadOnlyDictionary<TKey, TValue> Instance =
             new ReadOnlyDictionary<TKey, TValue>(new Dictionary<TKey, TValue>(0, EqualityComparer<TKey>.Default));
     }
-}
-
-public readonly record struct SchedulerQueueEnqueueResult(string MessageId, bool Deduplicated);
+}
+
+public readonly record struct SchedulerQueueEnqueueResult(string MessageId, bool Deduplicated);
 
 public sealed class SchedulerQueueLeaseRequest
 {
@@ -215,12 +214,32 @@ public sealed class SchedulerQueueClaimOptions
         MinIdleTime = minIdleTime;
     }
 
-    public string ClaimantConsumer { get; }
-
-    public int BatchSize { get; }
-
-    public TimeSpan MinIdleTime { get; }
-}
+    public string ClaimantConsumer { get; }
+
+    public int BatchSize { get; }
+
+    public TimeSpan MinIdleTime { get; }
+}
+
+/// <summary>
+/// Minimal pointer to a Surface.FS manifest associated with an image digest.
+/// Kept local to avoid coupling queue contracts to worker assemblies.
+/// </summary>
+public sealed record SurfaceManifestPointer
+{
+    public SurfaceManifestPointer(string manifestDigest, string? tenant)
+    {
+        ManifestDigest = manifestDigest ?? throw new ArgumentNullException(nameof(manifestDigest));
+        Tenant = tenant;
+    }
+
+    [JsonPropertyName("manifestDigest")]
+    public string ManifestDigest { get; init; }
+
+    [JsonPropertyName("tenant")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public string? Tenant { get; init; }
+}
 
 public enum SchedulerQueueReleaseDisposition
 {