feat: Add in-memory implementations for issuer audit, key, repository, and trust management

- Introduced InMemoryIssuerAuditSink to retain audit entries for testing.
- Implemented InMemoryIssuerKeyRepository for deterministic key storage.
- Created InMemoryIssuerRepository to manage issuer records in memory.
- Added InMemoryIssuerTrustRepository for managing issuer trust overrides.
- Each repository utilizes concurrent collections for thread-safe operations.
- Enhanced deprecation tracking with a comprehensive YAML schema for API governance.

src/Scanner/__Libraries/StellaOps.Scanner.Reachability/ReachabilityGraphBuilder.cs

@@ -44,7 +44,9 @@ public sealed class ReachabilityGraphBuilder
         string? display = null,
         string? sourceFile = null,
         int? sourceLine = null,
-        IReadOnlyDictionary<string, string>? attributes = null)
+        IReadOnlyDictionary<string, string>? attributes = null,
+        string? purl = null,
+        string? symbolDigest = null)
     {
         if (string.IsNullOrWhiteSpace(symbolId))
         {
@@ -59,7 +61,9 @@ public sealed class ReachabilityGraphBuilder
             display?.Trim(),
             sourceFile?.Trim(),
             sourceLine,
-            attributes?.ToImmutableSortedDictionary(StringComparer.Ordinal) ?? ImmutableSortedDictionary<string, string>.Empty);
+            attributes?.ToImmutableSortedDictionary(StringComparer.Ordinal) ?? ImmutableSortedDictionary<string, string>.Empty,
+            purl?.Trim(),
+            symbolDigest?.Trim());
 
         _richNodes[id] = node;
         nodes.Add(id);
@@ -93,6 +97,9 @@ public sealed class ReachabilityGraphBuilder
     /// <param name="origin">Origin: static or runtime.</param>
     /// <param name="provenance">Provenance hint: jvm-bytecode, il, ts-ast, ssa, ebpf, etw, jfr, hook.</param>
     /// <param name="evidence">Evidence locator (e.g., "file:path:line").</param>
+    /// <param name="purl">PURL of the component that defines the callee.</param>
+    /// <param name="symbolDigest">Stable hash of the normalized callee signature.</param>
+    /// <param name="candidates">Ranked candidate purls when resolution is ambiguous.</param>
     public ReachabilityGraphBuilder AddEdge(
         string from,
         string to,
@@ -100,7 +107,10 @@ public sealed class ReachabilityGraphBuilder
         EdgeConfidence confidence,
         string origin = "static",
         string? provenance = null,
-        string? evidence = null)
+        string? evidence = null,
+        string? purl = null,
+        string? symbolDigest = null,
+        IReadOnlyList<(string Purl, string? SymbolDigest, double? Score)>? candidates = null)
     {
         if (string.IsNullOrWhiteSpace(from) || string.IsNullOrWhiteSpace(to))
         {
@@ -118,7 +128,10 @@ public sealed class ReachabilityGraphBuilder
             confidence,
             origin?.Trim() ?? "static",
             provenance?.Trim(),
-            evidence?.Trim());
+            evidence?.Trim(),
+            purl?.Trim(),
+            symbolDigest?.Trim(),
+            candidates);
 
         _richEdges.Add(richEdge);
         nodes.Add(fromId);
@@ -172,7 +185,9 @@ public sealed class ReachabilityGraphBuilder
                     rich.Kind,
                     rich.Display,
                     source,
-                    rich.Attributes.Count > 0 ? rich.Attributes : null));
+                    rich.Attributes.Count > 0 ? rich.Attributes : null,
+                    rich.Purl,
+                    rich.SymbolDigest));
             }
             else
             {
@@ -199,12 +214,17 @@ public sealed class ReachabilityGraphBuilder
                 rich.Provenance,
                 rich.Evidence);
 
+            var candidates = rich.Candidates?.Select(c => new ReachabilityEdgeCandidate(c.Purl, c.SymbolDigest, c.Score)).ToList();
+
             edgeList.Add(new ReachabilityUnionEdge(
                 rich.From,
                 rich.To,
                 rich.EdgeType,
                 ConfidenceToString(rich.Confidence),
-                source));
+                source,
+                rich.Purl,
+                rich.SymbolDigest,
+                candidates));
         }
 
         // Add any legacy edges not already covered
@@ -315,7 +335,9 @@ public sealed class ReachabilityGraphBuilder
         string? Display,
         string? SourceFile,
         int? SourceLine,
-        ImmutableSortedDictionary<string, string> Attributes);
+        ImmutableSortedDictionary<string, string> Attributes,
+        string? Purl = null,
+        string? SymbolDigest = null);
 
     private sealed record RichEdge(
         string From,
@@ -324,7 +346,10 @@ public sealed class ReachabilityGraphBuilder
         EdgeConfidence Confidence,
         string Origin,
         string? Provenance,
-        string? Evidence);
+        string? Evidence,
+        string? Purl = null,
+        string? SymbolDigest = null,
+        IReadOnlyList<(string Purl, string? SymbolDigest, double? Score)>? Candidates = null);
 }
 
 /// <summary>