refactor(csharp): simplify loader-unification code

Tightens the recently-landed loader unification (DirectorySource, UriSource,
MetaDataLoader.FromDirectory/FromUris/FromString factories) without touching
any public name or behavior. All 526 tests still pass.

- Centralize extension→MetaDataFormat inference in MetaDataFormats.InferFromExtension
  (MetaDataSource.cs), eliminating the duplicated yaml/yml ternary in both
  FileSource and UriSource.
- Collapse MetaDataLoader's three-step constructor chain to one zero-arg ctor
  plus the full ctor with default args (freeze=true, strict=false); the
  intermediate (TypeRegistry) overload is still source-compatible via defaults.
- Merge two back-to-back `if (root is not null)` blocks in Load() around the
  super-resolution + validation-pass section into a single guarded block.
- Update server/csharp/README.md Loader/ inventory to reflect the rename
  (InMemorySource → InMemoryStringSource), the new DirectorySource + UriSource,
  the FromDirectory/FromUris/FromString factories, and the retirement of
  FileMetaDataLoader.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: dmealing

server/csharp/MetaObjects/Loader/FileSource.cs

@@ -22,11 +22,7 @@ public FileSource(string path)
     {
         FilePath = path;
         Id = System.IO.Path.GetFileName(path);
-        string ext = System.IO.Path.GetExtension(path);
-        Format = ext.Equals(".yaml", StringComparison.OrdinalIgnoreCase)
-                 || ext.Equals(".yml", StringComparison.OrdinalIgnoreCase)
-            ? MetaDataFormat.Yaml
-            : MetaDataFormat.Json;
+        Format = MetaDataFormats.InferFromExtension(path);
     }
 
     /// <summary>

server/csharp/MetaObjects/Loader/MetaDataLoader.cs

@@ -44,19 +44,11 @@ public class MetaDataLoader
     // Constructors
     // -------------------------------------------------------------------------
 
-    /// <summary>
-    /// Construct with the default core-types registry, freeze=true, strict=false.
-    /// </summary>
+    /// <summary>Construct with the default core-types registry, freeze=true, strict=false.</summary>
     public MetaDataLoader()
         : this(DefaultRegistry()) { }
 
-    /// <summary>
-    /// Construct with a custom registry, freeze=true, strict=false.
-    /// </summary>
-    public MetaDataLoader(TypeRegistry registry)
-        : this(registry, freeze: true, strict: false) { }
-
-    /// <summary>Full constructor — registry, freeze, strict all configurable.</summary>
+    /// <summary>Full constructor — registry required; freeze and strict configurable (defaults: freeze=true, strict=false).</summary>
     public MetaDataLoader(TypeRegistry registry, bool freeze = true, bool strict = false)
     {
         _registry = registry;
@@ -254,21 +246,17 @@ public LoadResult Load(IReadOnlyList<IMetaDataSource> sources)
         }
 
         // After the merge loop, BEFORE freeze — validation passes.
-
-        // Pass 1: resolveDeferredSupers — resolve cross-file extends refs against the full merged root.
         if (root is not null)
         {
+            // Pass 1: resolveDeferredSupers — resolve cross-file extends refs against the full merged root.
             var failures = SuperResolve.ResolveDeferredSupers(root);
             foreach (var failure in failures)
             {
                 errors.Add(new MetaError(
                     $"the SuperClass '{failure.Ref}' does not exist (referenced by {failure.NodeFqn})",
                     ErrorCode.ERR_UNRESOLVED_SUPER));
             }
-        }
 
-        if (root is not null)
-        {
             // Pass 2: subtype rules (value must not have primary identity; entity should have one)
             var subtypeResult = ValidationPasses.ValidateSubtypeRules(root);
             errors.AddRange(subtypeResult.Errors);

server/csharp/MetaObjects/Loader/MetaDataSource.cs

@@ -21,6 +21,20 @@ public interface IMetaDataSource
     string Read();
 }
 
+/// <summary>Shared helpers for <see cref="IMetaDataSource"/> implementations.</summary>
+internal static class MetaDataFormats
+{
+    /// <summary>Infer <see cref="MetaDataFormat"/> from a path/URI extension. Unknown → JSON.</summary>
+    internal static MetaDataFormat InferFromExtension(string path)
+    {
+        string ext = System.IO.Path.GetExtension(path);
+        return ext.Equals(".yaml", StringComparison.OrdinalIgnoreCase)
+               || ext.Equals(".yml", StringComparison.OrdinalIgnoreCase)
+            ? MetaDataFormat.Yaml
+            : MetaDataFormat.Json;
+    }
+}
+
 /// <summary>A metadata source backed by an in-memory string.</summary>
 public sealed class InMemoryStringSource : IMetaDataSource
 {

server/csharp/MetaObjects/Loader/UriSource.cs

@@ -31,7 +31,7 @@ public UriSource(Uri uri, MetaDataFormat? format = null)
     {
         Uri = uri ?? throw new ArgumentNullException(nameof(uri));
         Id = uri.ToString();
-        Format = format ?? InferFormatFromExtension(uri.AbsolutePath);
+        Format = format ?? MetaDataFormats.InferFromExtension(uri.AbsolutePath);
     }
 
     public string Read()
@@ -50,13 +50,4 @@ public string Read()
 
         throw new NotSupportedException($"Unsupported URI scheme '{Uri.Scheme}' on {Uri}");
     }
-
-    private static MetaDataFormat InferFormatFromExtension(string path)
-    {
-        string ext = Path.GetExtension(path);
-        return ext.Equals(".yaml", StringComparison.OrdinalIgnoreCase)
-               || ext.Equals(".yml", StringComparison.OrdinalIgnoreCase)
-            ? MetaDataFormat.Yaml
-            : MetaDataFormat.Json;
-    }
 }

server/csharp/README.md

@@ -32,7 +32,7 @@ The test suite includes per-fixture `Lint` and `Conformance` theories over the s
   - `CoreAttrSchemas.cs`, `CoreTypes.cs` — the `metaobjects-core-types` provider
   - `Parser.cs`, `SuperResolve.cs`, `SerializerJson.cs`
   - `YamlDesugar.cs`, `ParserYaml.cs` — YAML authoring front-end (ADR-0006)
-  - `Loader/` — `IMetaDataSource`, `InMemorySource`, `FileSource`, `MetaDataLoader`, `FileMetaDataLoader`, `ValidationPasses`
+  - `Loader/` — `IMetaDataSource`, `InMemoryStringSource`, `FileSource`, `DirectorySource`, `UriSource`, `MetaDataLoader` (with `FromDirectory`/`FromUris`/`FromString` static factories), `ValidationPasses`
 - `MetaObjects.Conformance.Tests/` — xUnit test project + conformance harness
   - `ConformanceAdapter.cs`, `FixtureDiscovery.cs`, `OperationScript.cs`, `FixtureLint.cs`, `Navigator.cs`, `CapabilityBinding.cs`, `Result.cs`, `ExpectedFailures.cs`, `conformance-expected-failures.json`, `ConformanceTests.cs`
   - `YamlConformanceTests.cs`, `YamlDesugarTests.cs`, `yaml-conformance-expected-failures.json` — YAML conformance + unit tests