Add integration tests for Proof Chain and Reachability workflows

- Implement ProofChainTestFixture for PostgreSQL-backed integration tests.
- Create StellaOps.Integration.ProofChain project with necessary dependencies.
- Add ReachabilityIntegrationTests to validate call graph extraction and reachability analysis.
- Introduce ReachabilityTestFixture for managing corpus and fixture paths.
- Establish StellaOps.Integration.Reachability project with required references.
- Develop UnknownsWorkflowTests to cover the unknowns lifecycle: detection, ranking, escalation, and resolution.
- Create StellaOps.Integration.Unknowns project with dependencies for unknowns workflow.

tests/integration/StellaOps.Integration.Performance/PerformanceTestFixture.cs

@@ -0,0 +1,147 @@
+// =============================================================================
+// StellaOps.Integration.Performance - Performance Test Fixture
+// Sprint 3500.0004.0003 - T7: Performance Baseline Tests
+// =============================================================================
+
+using System.Text.Json;
+
+namespace StellaOps.Integration.Performance;
+
+/// <summary>
+/// Test fixture for performance baseline tests.
+/// Manages baseline data and measurement recording.
+/// </summary>
+public sealed class PerformanceTestFixture : IDisposable
+{
+    private readonly string _baselinesPath;
+    private readonly string _outputPath;
+    private readonly Dictionary<string, double> _baselines;
+    private readonly Dictionary<string, double> _measurements = new();
+
+    public PerformanceTestFixture()
+    {
+        _baselinesPath = Path.Combine(AppContext.BaseDirectory, "baselines");
+        _outputPath = Path.Combine(AppContext.BaseDirectory, "output");
+
+        Directory.CreateDirectory(_outputPath);
+
+        _baselines = LoadBaselines();
+    }
+
+    /// <summary>
+    /// Gets the baseline value for a metric.
+    /// Returns default if baseline not found.
+    /// </summary>
+    public double GetBaseline(string metric)
+    {
+        return _baselines.TryGetValue(metric, out var baseline) ? baseline : GetDefaultBaseline(metric);
+    }
+
+    /// <summary>
+    /// Records a measurement for a metric.
+    /// </summary>
+    public void RecordMeasurement(string metric, double value)
+    {
+        _measurements[metric] = value;
+    }
+
+    /// <summary>
+    /// Gets all recorded measurements.
+    /// </summary>
+    public IEnumerable<(string metric, double value)> GetAllMeasurements()
+    {
+        return _measurements.Select(kv => (kv.Key, kv.Value));
+    }
+
+    /// <summary>
+    /// Gets the path to a test assembly.
+    /// </summary>
+    public string GetTestAssemblyPath(string name)
+    {
+        var path = Path.Combine(AppContext.BaseDirectory, "test-assemblies", $"{name}.dll");
+        return File.Exists(path) ? path : Path.Combine(AppContext.BaseDirectory, "StellaOps.Integration.Performance.dll");
+    }
+
+    /// <summary>
+    /// Gets available test assemblies.
+    /// </summary>
+    public IEnumerable<(string Name, string Path)> GetTestAssemblies()
+    {
+        var testAssembliesDir = Path.Combine(AppContext.BaseDirectory, "test-assemblies");
+
+        if (Directory.Exists(testAssembliesDir))
+        {
+            foreach (var file in Directory.GetFiles(testAssembliesDir, "*.dll"))
+            {
+                yield return (Path.GetFileNameWithoutExtension(file), file);
+            }
+        }
+        else
+        {
+            // Use self as test assembly
+            var selfPath = Path.Combine(AppContext.BaseDirectory, "StellaOps.Integration.Performance.dll");
+            if (File.Exists(selfPath))
+            {
+                yield return ("Self", selfPath);
+            }
+        }
+    }
+
+    /// <summary>
+    /// Saves a report file.
+    /// </summary>
+    public void SaveReport(string filename, string content)
+    {
+        var path = Path.Combine(_outputPath, filename);
+        File.WriteAllText(path, content);
+    }
+
+    private Dictionary<string, double> LoadBaselines()
+    {
+        var baselinesFile = Path.Combine(_baselinesPath, "performance-baselines.json");
+
+        if (File.Exists(baselinesFile))
+        {
+            var json = File.ReadAllText(baselinesFile);
+            return JsonSerializer.Deserialize<Dictionary<string, double>>(json) ?? GetDefaultBaselines();
+        }
+
+        return GetDefaultBaselines();
+    }
+
+    private static Dictionary<string, double> GetDefaultBaselines()
+    {
+        return new Dictionary<string, double>
+        {
+            // Score computation
+            ["score_computation_ms"] = 100,
+            ["score_computation_large_ms"] = 500,
+
+            // Proof bundle
+            ["proof_bundle_generation_ms"] = 200,
+            ["proof_signing_ms"] = 50,
+
+            // Call graph
+            ["dotnet_callgraph_extraction_ms"] = 500,
+
+            // Reachability
+            ["reachability_computation_ms"] = 100,
+            ["reachability_large_graph_ms"] = 500,
+            ["reachability_deep_path_ms"] = 200
+        };
+    }
+
+    private static double GetDefaultBaseline(string metric)
+    {
+        // Default to 1 second for unknown metrics
+        return 1000;
+    }
+
+    public void Dispose()
+    {
+        // Save measurements for potential baseline updates
+        var measurementsFile = Path.Combine(_outputPath, "measurements.json");
+        var json = JsonSerializer.Serialize(_measurements, new JsonSerializerOptions { WriteIndented = true });
+        File.WriteAllText(measurementsFile, json);
+    }
+}