DET-004: Refactor Policy Replay and Deltas for determinism

- ReplayEngine: inject TimeProvider
- ReplayReport: inject TimeProvider and IGuidProvider via builder
- ReplayResult: add TimeProvider parameter to Failed() method
- DeltaComputer: inject TimeProvider
- DeltaVerdictBuilder: inject TimeProvider

Replace DateTimeOffset.UtcNow and Guid.NewGuid() with injected providers

Sprint: SPRINT_20260104_001_BE_determinism_timeprovider_injection

src/Policy/__Libraries/StellaOps.Policy/Deltas/DeltaComputer.cs

@@ -16,13 +16,16 @@ public sealed class DeltaComputer : IDeltaComputer
 {
     private readonly ISnapshotService _snapshotService;
     private readonly ILogger<DeltaComputer> _logger;
+    private readonly TimeProvider _timeProvider;
 
     public DeltaComputer(
         ISnapshotService snapshotService,
-        ILogger<DeltaComputer> logger)
+        ILogger<DeltaComputer> logger,
+        TimeProvider? timeProvider = null)
     {
         _snapshotService = snapshotService;
         _logger = logger;
+        _timeProvider = timeProvider ?? TimeProvider.System;
     }
 
     /// <inheritdoc />
@@ -58,7 +61,7 @@ public sealed class DeltaComputer : IDeltaComputer
         var delta = new SecurityStateDelta
         {
             DeltaId = "", // Computed below
-            ComputedAt = DateTimeOffset.UtcNow,
+            ComputedAt = _timeProvider.GetUtcNow(),
             BaselineSnapshotId = baselineSnapshotId,
             TargetSnapshotId = targetSnapshotId,
             Artifact = artifact,

src/Policy/__Libraries/StellaOps.Policy/Deltas/DeltaVerdict.cs

@@ -127,6 +127,7 @@ public sealed class DeltaVerdictBuilder
     private static readonly IVerdictIdGenerator DefaultIdGenerator = new VerdictIdGenerator();
 
     private readonly IVerdictIdGenerator _idGenerator;
+    private readonly TimeProvider _timeProvider;
     private DeltaVerdictStatus _status = DeltaVerdictStatus.Pass;
     private DeltaGateLevel _gate = DeltaGateLevel.G1;
     private int _riskPoints;
@@ -139,7 +140,7 @@ public sealed class DeltaVerdictBuilder
     /// <summary>
     /// Creates a new <see cref="DeltaVerdictBuilder"/> with the default ID generator.
     /// </summary>
-    public DeltaVerdictBuilder() : this(DefaultIdGenerator)
+    public DeltaVerdictBuilder() : this(DefaultIdGenerator, TimeProvider.System)
     {
     }
 
@@ -147,9 +148,11 @@ public sealed class DeltaVerdictBuilder
     /// Creates a new <see cref="DeltaVerdictBuilder"/> with a custom ID generator.
     /// </summary>
     /// <param name="idGenerator">Custom verdict ID generator for testing or specialized scenarios.</param>
-    public DeltaVerdictBuilder(IVerdictIdGenerator idGenerator)
+    /// <param name="timeProvider">Time provider for deterministic timestamps.</param>
+    public DeltaVerdictBuilder(IVerdictIdGenerator idGenerator, TimeProvider? timeProvider = null)
     {
         _idGenerator = idGenerator ?? throw new ArgumentNullException(nameof(idGenerator));
+        _timeProvider = timeProvider ?? TimeProvider.System;
     }
 
     public DeltaVerdictBuilder WithStatus(DeltaVerdictStatus status)
@@ -241,7 +244,7 @@ public sealed class DeltaVerdictBuilder
         {
             VerdictId = verdictId,
             DeltaId = deltaId,
-            EvaluatedAt = DateTimeOffset.UtcNow,
+            EvaluatedAt = _timeProvider.GetUtcNow(),
             Status = _status,
             RecommendedGate = _gate,
             RiskPoints = _riskPoints,

src/Policy/__Libraries/StellaOps.Policy/Replay/ReplayEngine.cs

@@ -14,16 +14,19 @@ public sealed class ReplayEngine : IReplayEngine
     private readonly IKnowledgeSourceResolver _sourceResolver;
     private readonly IVerdictComparer _verdictComparer;
     private readonly ILogger<ReplayEngine> _logger;
+    private readonly TimeProvider _timeProvider;
 
     public ReplayEngine(
         ISnapshotService snapshotService,
         IKnowledgeSourceResolver sourceResolver,
         IVerdictComparer verdictComparer,
+        TimeProvider? timeProvider = null,
         ILogger<ReplayEngine>? logger = null)
     {
         _snapshotService = snapshotService ?? throw new ArgumentNullException(nameof(snapshotService));
         _sourceResolver = sourceResolver ?? throw new ArgumentNullException(nameof(sourceResolver));
         _verdictComparer = verdictComparer ?? throw new ArgumentNullException(nameof(verdictComparer));
+        _timeProvider = timeProvider ?? TimeProvider.System;
         _logger = logger ?? NullLogger<ReplayEngine>.Instance;
     }
 
@@ -89,7 +92,7 @@ public sealed class ReplayEngine : IReplayEngine
             OriginalVerdict = originalVerdict,
             DeltaReport = deltaReport,
             SnapshotId = request.SnapshotId,
-            ReplayedAt = DateTimeOffset.UtcNow,
+            ReplayedAt = _timeProvider.GetUtcNow(),
             Duration = stopwatch.Elapsed
         };
     }

src/Policy/__Libraries/StellaOps.Policy/Replay/ReplayReport.cs

@@ -1,3 +1,5 @@
+using StellaOps.Determinism;
+
 namespace StellaOps.Policy.Replay;
 
 /// <summary>
@@ -111,11 +113,19 @@ public sealed class ReplayReportBuilder
     private readonly ReplayResult _result;
     private readonly ReplayRequest _request;
     private readonly List<string> _recommendations = [];
+    private readonly TimeProvider _timeProvider;
+    private readonly IGuidProvider _guidProvider;
 
-    public ReplayReportBuilder(ReplayRequest request, ReplayResult result)
+    public ReplayReportBuilder(
+        ReplayRequest request,
+        ReplayResult result,
+        TimeProvider? timeProvider = null,
+        IGuidProvider? guidProvider = null)
     {
         _request = request ?? throw new ArgumentNullException(nameof(request));
         _result = result ?? throw new ArgumentNullException(nameof(result));
+        _timeProvider = timeProvider ?? TimeProvider.System;
+        _guidProvider = guidProvider ?? SystemGuidProvider.Instance;
     }
 
     public ReplayReportBuilder AddRecommendation(string recommendation)
@@ -150,8 +160,8 @@ public sealed class ReplayReportBuilder
     {
         return new ReplayReport
         {
-            ReportId = $"rpt:{Guid.NewGuid():N}",
-            GeneratedAt = DateTimeOffset.UtcNow,
+            ReportId = $"rpt:{_guidProvider.NewGuid():N}",
+            GeneratedAt = _timeProvider.GetUtcNow(),
             ArtifactDigest = _request.ArtifactDigest,
             SnapshotId = _request.SnapshotId,
             OriginalVerdictId = _request.OriginalVerdictId,

src/Policy/__Libraries/StellaOps.Policy/Replay/ReplayResult.cs

@@ -43,12 +43,12 @@ public sealed record ReplayResult
     /// <summary>
     /// Creates a failed result.
     /// </summary>
-    public static ReplayResult Failed(string snapshotId, string error) => new()
+    public static ReplayResult Failed(string snapshotId, string error, TimeProvider? timeProvider = null) => new()
     {
         MatchStatus = ReplayMatchStatus.ReplayFailed,
         ReplayedVerdict = ReplayedVerdict.Empty,
         SnapshotId = snapshotId,
-        ReplayedAt = DateTimeOffset.UtcNow,
+        ReplayedAt = (timeProvider ?? TimeProvider.System).GetUtcNow(),
         DeltaReport = new ReplayDeltaReport
         {
             Summary = error,