Implement engine-bridge PoC v1 (#9)

- Add Recordingtest.EngineBridge library (IEngineSnapshot, HmEgSnapshot
  skeleton, MetadataLoader, CandidateFinder, CatalogWriter).
- Add Recordingtest.EngineBridge.Probe console exe that dumps
  hmeg-types.json and hmeg-candidates.json to docs/engine-catalog.
- Add Recordingtest.EngineBridge.Tests (xUnit, 6 tests).
- Add probe design doc with plugin-masquerade recommendation.
- Static analysis only; SUT is never executed.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/Recordingtest.EngineBridge.Probe/Program.cs

@@ -0,0 +1,87 @@
+using System.Reflection;
+using Recordingtest.EngineBridge;
+
+namespace Recordingtest.EngineBridge.Probe;
+
+internal static class Program
+{
+    private static readonly string[] DefaultAssemblyPatterns =
+    {
+        "HmEG.dll",
+        "HmGeometry.dll",
+        "HmGeometry.V2.dll",
+        "HmTriangle.dll",
+        "EditorCore.dll",
+        "Editor*.dll",
+    };
+
+    internal static int Main(string[] args)
+    {
+        string sutRoot = "EG-BIM Modeler";
+        string outDir = Path.Combine("docs", "engine-catalog");
+
+        for (int i = 0; i < args.Length; i++)
+        {
+            switch (args[i])
+            {
+                case "--sut" when i + 1 < args.Length:
+                    sutRoot = args[++i];
+                    break;
+                case "--out" when i + 1 < args.Length:
+                    outDir = args[++i];
+                    break;
+            }
+        }
+
+        if (!Directory.Exists(sutRoot))
+        {
+            Console.Error.WriteLine($"SUT path not found: {sutRoot}");
+            return 2;
+        }
+
+        var assemblyNames = ResolveAssemblyNames(sutRoot);
+        Console.WriteLine($"Loading {assemblyNames.Count} assemblies from {sutRoot}");
+
+        using var loader = new MetadataLoader(sutRoot);
+        var types = loader.LoadTypes(assemblyNames).ToList();
+
+        var byAsm = types
+            .GroupBy(t => t.Assembly.GetName().Name ?? "?")
+            .OrderBy(g => g.Key, StringComparer.Ordinal);
+        foreach (var g in byAsm)
+        {
+            Console.WriteLine($"  {g.Key}: {g.Count()} types");
+        }
+
+        var candidates = CandidateFinder.Find(types);
+        var byCat = candidates
+            .GroupBy(c => c.Category)
+            .OrderBy(g => g.Key, StringComparer.Ordinal);
+        Console.WriteLine("Candidate categories:");
+        foreach (var g in byCat)
+        {
+            Console.WriteLine($"  {g.Key}: {g.Count()}");
+        }
+
+        var typesPath = Path.Combine(outDir, "hmeg-types.json").Replace('\\', '/');
+        var candPath = Path.Combine(outDir, "hmeg-candidates.json").Replace('\\', '/');
+        CatalogWriter.WriteTypes(typesPath, types);
+        CatalogWriter.WriteCandidates(candPath, candidates);
+        Console.WriteLine($"Wrote {typesPath}");
+        Console.WriteLine($"Wrote {candPath}");
+        return 0;
+    }
+
+    private static List<string> ResolveAssemblyNames(string sutRoot)
+    {
+        var set = new SortedSet<string>(StringComparer.Ordinal);
+        foreach (var pat in DefaultAssemblyPatterns)
+        {
+            foreach (var f in Directory.EnumerateFiles(sutRoot, pat, SearchOption.TopDirectoryOnly))
+            {
+                set.Add(Path.GetFileName(f));
+            }
+        }
+        return set.ToList();
+    }
+}

src/Recordingtest.EngineBridge.Probe/Recordingtest.EngineBridge.Probe.csproj

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <AssemblyName>Recordingtest.EngineBridge.Probe</AssemblyName>
+    <RootNamespace>Recordingtest.EngineBridge.Probe</RootNamespace>
+  </PropertyGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\Recordingtest.EngineBridge\Recordingtest.EngineBridge.csproj" />
+  </ItemGroup>
+</Project>