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/tree-sitter.ts

@@ -1238,8 +1238,10 @@ export class TreeSitterExtractor {
     if (!this.extractor) return;
 
     // Skip forward declarations and type references (no body = not a definition)
+    // — EXCEPT C# positional records (`record struct M(decimal Amount);`),
+    // complete definitions with no body block. (#831)
     const body = getChildByField(node, this.extractor.bodyField);
-    if (!body) return;
+    if (!body && node.type !== 'record_declaration') return;
 
     const name = extractName(node, this.source, this.extractor);
     const docstring = getPrecedingDocstring(node, this.source);
@@ -1260,15 +1262,18 @@ export class TreeSitterExtractor {
     // `record struct M(decimal Amount)` which the grammar nests here).
     this.extractCsharpPrimaryCtorParamRefs(node, structNode.id);
 
-    // Push to stack for field extraction
-    this.nodeStack.push(structNode.id);
-    for (let i = 0; i < body.namedChildCount; i++) {
-      const child = body.namedChild(i);
-      if (child) {
-        this.visitNode(child);
+    // Push to stack for field extraction (bodiless positional records have
+    // no members to visit)
+    if (body) {
+      this.nodeStack.push(structNode.id);
+      for (let i = 0; i < body.namedChildCount; i++) {
+        const child = body.namedChild(i);
+        if (child) {
+          this.visitNode(child);
+        }
       }
+      this.nodeStack.pop();
     }
-    this.nodeStack.pop();
   }
 
   /**