Add signal contracts for reachability, exploitability, trust, and unknown symbols

- Introduced `ReachabilityState`, `RuntimeHit`, `ExploitabilitySignal`, `ReachabilitySignal`, `SignalEnvelope`, `SignalType`, `TrustSignal`, and `UnknownSymbolSignal` records to define various signal types and their properties.
- Implemented JSON serialization attributes for proper data interchange.
- Created project files for the new signal contracts library and corresponding test projects.
- Added deterministic test fixtures for micro-interaction testing.
- Included cryptographic keys for secure operations with cosign.

src/Policy/StellaOps.Policy.Engine/Endpoints/RiskProfileEndpoints.cs

@@ -82,6 +82,12 @@ internal static class RiskProfileEndpoints
             .Produces<RiskProfileHashResponse>(StatusCodes.Status200OK)
             .Produces<ProblemHttpResult>(StatusCodes.Status404NotFound);
 
+        group.MapGet("/{profileId}/metadata", GetProfileMetadata)
+            .WithName("GetRiskProfileMetadata")
+            .WithSummary("Export risk profile metadata for notification enrichment (POLICY-RISK-40-002).")
+            .Produces<RiskProfileMetadataExportResponse>(StatusCodes.Status200OK)
+            .Produces<ProblemHttpResult>(StatusCodes.Status404NotFound);
+
         return endpoints;
     }
 
@@ -461,6 +467,53 @@ internal static class RiskProfileEndpoints
         return Results.Ok(new RiskProfileHashResponse(profile.Id, profile.Version, hash, contentOnly));
     }
 
+    private static IResult GetProfileMetadata(
+        HttpContext context,
+        [FromRoute] string profileId,
+        RiskProfileConfigurationService profileService,
+        RiskProfileLifecycleService lifecycleService)
+    {
+        var scopeResult = ScopeAuthorization.RequireScope(context, StellaOpsScopes.PolicyRead);
+        if (scopeResult is not null)
+        {
+            return scopeResult;
+        }
+
+        var profile = profileService.GetProfile(profileId);
+        if (profile == null)
+        {
+            return Results.NotFound(new ProblemDetails
+            {
+                Title = "Profile not found",
+                Detail = $"Risk profile '{profileId}' was not found.",
+                Status = StatusCodes.Status404NotFound
+            });
+        }
+
+        var versions = lifecycleService.GetAllVersions(profileId);
+        var activeVersion = versions.FirstOrDefault(v => v.Status == RiskProfileLifecycleStatus.Active);
+        var hash = profileService.ComputeHash(profile);
+
+        // Extract signal names and severity thresholds for notification context
+        var signalNames = profile.Signals.Select(s => s.Name).ToList();
+        var severityThresholds = profile.Overrides.Severity
+            .Select(s => new SeverityThresholdInfo(s.Set.ToString(), s.When))
+            .ToList();
+
+        return Results.Ok(new RiskProfileMetadataExportResponse(
+            ProfileId: profile.Id,
+            Version: profile.Version,
+            Description: profile.Description,
+            Hash: hash,
+            Status: activeVersion?.Status.ToString() ?? "unknown",
+            SignalNames: signalNames,
+            SeverityThresholds: severityThresholds,
+            CustomMetadata: profile.Metadata,
+            ExtendsProfile: profile.Extends,
+            ExportedAt: DateTime.UtcNow
+        ));
+    }
+
     private static string? ResolveActorId(HttpContext context)
     {
         var user = context.User;
@@ -521,4 +574,26 @@ internal sealed record CompareRiskProfilesRequest(
     string ToProfileId,
     string ToVersion);
 
+/// <summary>
+/// Metadata export response for notification enrichment (POLICY-RISK-40-002).
+/// </summary>
+internal sealed record RiskProfileMetadataExportResponse(
+    string ProfileId,
+    string Version,
+    string? Description,
+    string Hash,
+    string Status,
+    IReadOnlyList<string> SignalNames,
+    IReadOnlyList<SeverityThresholdInfo> SeverityThresholds,
+    Dictionary<string, object?>? CustomMetadata,
+    string? ExtendsProfile,
+    DateTime ExportedAt);
+
+/// <summary>
+/// Severity threshold information for notification context.
+/// </summary>
+internal sealed record SeverityThresholdInfo(
+    string TargetSeverity,
+    Dictionary<string, object> WhenConditions);
+
 #endregion