feat: Implement Runtime Facts ingestion service and NDJSON reader

- Added RuntimeFactsNdjsonReader for reading NDJSON formatted runtime facts.
- Introduced IRuntimeFactsIngestionService interface and its implementation.
- Enhanced Program.cs to register new services and endpoints for runtime facts.
- Updated CallgraphIngestionService to include CAS URI in stored artifacts.
- Created RuntimeFactsValidationException for validation errors during ingestion.
- Added tests for RuntimeFactsIngestionService and RuntimeFactsNdjsonReader.
- Implemented SignalsSealedModeMonitor for compliance checks in sealed mode.
- Updated project dependencies for testing utilities.

src/Signals/StellaOps.Signals/Models/CallgraphArtifactMetadata.cs

@@ -7,15 +7,18 @@ namespace StellaOps.Signals.Models;
 /// </summary>
 public sealed class CallgraphArtifactMetadata
 {
-    [BsonElement("path")]
-    public string Path { get; set; } = string.Empty;
-
-    [BsonElement("hash")]
-    public string Hash { get; set; } = string.Empty;
-
-    [BsonElement("contentType")]
-    public string ContentType { get; set; } = string.Empty;
-
+    [BsonElement("path")]
+    public string Path { get; set; } = string.Empty;
+
+    [BsonElement("hash")]
+    public string Hash { get; set; } = string.Empty;
+
+    [BsonElement("casUri")]
+    public string CasUri { get; set; } = string.Empty;
+
+    [BsonElement("contentType")]
+    public string ContentType { get; set; } = string.Empty;
+
     [BsonElement("length")]
     public long Length { get; set; }
 }

src/Signals/StellaOps.Signals/Models/CallgraphIngestResponse.cs

@@ -3,7 +3,8 @@ namespace StellaOps.Signals.Models;
 /// <summary>
 /// Response returned after callgraph ingestion.
 /// </summary>
-public sealed record CallgraphIngestResponse(
-    string CallgraphId,
-    string ArtifactPath,
-    string ArtifactHash);
+public sealed record CallgraphIngestResponse(
+    string CallgraphId,
+    string ArtifactPath,
+    string ArtifactHash,
+    string CasUri);

src/Signals/StellaOps.Signals/Models/ReachabilityFactDocument.cs

@@ -23,6 +23,10 @@ public sealed class ReachabilityFactDocument
     [BsonElement("states")]
     public List<ReachabilityStateDocument> States { get; set; } = new();
 
+    [BsonElement("runtimeFacts")]
+    [BsonIgnoreIfNull]
+    public List<RuntimeFactDocument>? RuntimeFacts { get; set; }
+
     [BsonElement("metadata")]
     [BsonIgnoreIfNull]
     public Dictionary<string, string?>? Metadata { get; set; }
@@ -96,3 +100,24 @@ public sealed class ReachabilitySubject
         return string.Join('|', Component ?? string.Empty, Version ?? string.Empty).Trim('|');
     }
 }
+
+public sealed class RuntimeFactDocument
+{
+    [BsonElement("symbolId")]
+    public string SymbolId { get; set; } = string.Empty;
+
+    [BsonElement("codeId")]
+    [BsonIgnoreIfNull]
+    public string? CodeId { get; set; }
+
+    [BsonElement("loaderBase")]
+    [BsonIgnoreIfNull]
+    public string? LoaderBase { get; set; }
+
+    [BsonElement("hitCount")]
+    public int HitCount { get; set; }
+
+    [BsonElement("metadata")]
+    [BsonIgnoreIfNull]
+    public Dictionary<string, string?>? Metadata { get; set; }
+}

src/Signals/StellaOps.Signals/Models/RuntimeFactsIngestRequest.cs

@@ -0,0 +1,47 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+
+namespace StellaOps.Signals.Models;
+
+public sealed class RuntimeFactsIngestRequest
+{
+    [Required]
+    public ReachabilitySubject Subject { get; set; } = new();
+
+    [Required]
+    public string CallgraphId { get; set; } = string.Empty;
+
+    public List<RuntimeFactEvent> Events { get; set; } = new();
+
+    public Dictionary<string, string?>? Metadata { get; set; }
+}
+
+public sealed class RuntimeFactEvent
+{
+    [Required]
+    public string SymbolId { get; set; } = string.Empty;
+
+    public string? CodeId { get; set; }
+
+    public string? LoaderBase { get; set; }
+
+    public int HitCount { get; set; } = 1;
+
+    public Dictionary<string, string?>? Metadata { get; set; }
+}
+
+public sealed class RuntimeFactsIngestResponse
+{
+    public string FactId { get; init; } = string.Empty;
+
+    public string SubjectKey { get; init; } = string.Empty;
+
+    public string CallgraphId { get; init; } = string.Empty;
+
+    public int RuntimeFactCount { get; init; }
+
+    public int TotalHitCount { get; init; }
+
+    public DateTimeOffset StoredAt { get; init; }
+}

src/Signals/StellaOps.Signals/Models/RuntimeFactsStreamMetadata.cs

@@ -0,0 +1,14 @@
+namespace StellaOps.Signals.Models;
+
+public sealed class RuntimeFactsStreamMetadata
+{
+    public string CallgraphId { get; set; } = string.Empty;
+
+    public string? ScanId { get; set; }
+
+    public string? ImageDigest { get; set; }
+
+    public string? Component { get; set; }
+
+    public string? Version { get; set; }
+}