fix(extraction): C# record-struct kind fidelity + bodiless positional records (#831 follow-up) (#838)

The shipped grammar parses every record form as record_declaration (no
record_struct_declaration node), so 'record struct' mis-kinded as class.
classifyClassNode now distinguishes the value-type form by its struct
keyword child, and extractStruct accepts bodiless positional records
(the no-body gate is for C/C++ forward declarations) instead of
crashing mid-file on them.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

src/extraction/languages/csharp.ts

@@ -56,13 +56,24 @@ export const csharpExtractor: LanguageExtractor = {
   preParse: blankCsharpPreprocessorDirectives,
   functionTypes: [],
   // Records are first-class type declarations in modern C# (DTOs, value objects,
-  // MediatR/CQRS messages). `record` / `record class` parse as record_declaration
-  // (reference type → class); `record struct` as record_struct_declaration (value
-  // type → struct). Without these, references to a record never resolve (#237).
+  // MediatR/CQRS messages). Without these, references to a record never resolve
+  // (#237). The shipped grammar parses EVERY record form as record_declaration —
+  // `record struct` / `readonly record struct` included (it has no
+  // record_struct_declaration node; that structTypes entry is forward-compat
+  // only) — so classifyClassNode tells the value-type form apart by its
+  // `struct` keyword child. (#831 follow-up)
   classTypes: ['class_declaration', 'record_declaration'],
   methodTypes: ['method_declaration', 'constructor_declaration'],
   interfaceTypes: ['interface_declaration'],
   structTypes: ['struct_declaration', 'record_struct_declaration'],
+  classifyClassNode: (node) => {
+    if (node.type === 'record_declaration') {
+      for (let i = 0; i < node.childCount; i++) {
+        if (node.child(i)?.type === 'struct') return 'struct';
+      }
+    }
+    return 'class';
+  },
   enumTypes: ['enum_declaration'],
   enumMemberTypes: ['enum_member_declaration'],
   typeAliasTypes: [],