test(rust): cover Box<dyn Trait> and dyn-bound-list normalization (#2604)

GitNexus review-agent finding: stripDynBound's documented Box<dyn Trait>,
Rc/Arc<dyn Trait>, and auto-trait/lifetime bound-list (dyn Trait + Send)
shapes had no test anywhere — only the bare &dyn Trait parameter case was
exercised end-to-end. Add direct unit coverage on normalizeRustTypeName and
(via interpretRustTypeBinding) normalizeRustReturnType for these shapes.

gitnexus/test/unit/scope-resolution/rust/rust-dyn-type-normalization.test.ts

@@ -0,0 +1,61 @@
+import { describe, expect, it } from 'vitest';
+import type { CaptureMatch } from 'gitnexus-shared';
+import {
+  normalizeRustTypeName,
+  interpretRustTypeBinding,
+} from '../../../../src/core/ingestion/languages/rust/interpret.js';
+
+const RANGE = { startLine: 0, startCol: 0, endLine: 0, endCol: 0 };
+
+/** Builds a minimal @type-binding.return CaptureMatch to exercise
+ *  normalizeRustReturnType (private, only reachable through this hook). */
+function returnTypeBinding(type: string): CaptureMatch {
+  return {
+    '@type-binding.name': { name: '@type-binding.name', range: RANGE, text: 'f' },
+    '@type-binding.type': { name: '@type-binding.type', range: RANGE, text: type },
+    '@type-binding.return': { name: '@type-binding.return', range: RANGE, text: '' },
+  };
+}
+
+/**
+ * #2604 coverage gap (GitNexus review-agent finding): stripDynBound's
+ * documented Box<dyn Trait> and bound-list (dyn Trait + Send) shapes had no
+ * test anywhere, even though the interpret.ts comment claims they're handled.
+ * These exercise normalizeRustTypeName/normalizeRustReturnType directly —
+ * stripDynBound itself is a private helper reached only through them.
+ */
+describe('Rust dyn-trait-object type-name normalization (#2604)', () => {
+  it('strips a bare dyn Trait parameter type', () => {
+    expect(normalizeRustTypeName('&dyn Behaviour')).toBe('Behaviour');
+    expect(normalizeRustTypeName('dyn Behaviour')).toBe('Behaviour');
+  });
+
+  it('strips dyn through Box/Rc/Arc wrappers', () => {
+    expect(normalizeRustTypeName('Box<dyn Trait>')).toBe('Trait');
+    expect(normalizeRustTypeName('Rc<dyn Trait>')).toBe('Trait');
+    expect(normalizeRustTypeName('Arc<dyn Trait>')).toBe('Trait');
+  });
+
+  it('drops an auto-trait/lifetime bound list after dyn', () => {
+    expect(normalizeRustTypeName('dyn Trait + Send')).toBe('Trait');
+    expect(normalizeRustTypeName("dyn Trait + Send + 'static")).toBe('Trait');
+    expect(normalizeRustTypeName("Box<dyn Trait + 'static>")).toBe('Trait');
+  });
+
+  it('truncates a dyn trait\'s own generic arguments after stripping dyn', () => {
+    expect(normalizeRustTypeName('dyn Iterator<Item = u32>')).toBe('Iterator');
+  });
+
+  it('strips dyn in return-type position, including through &', () => {
+    expect(interpretRustTypeBinding(returnTypeBinding('&dyn Trait'))?.rawTypeName).toBe('Trait');
+    expect(interpretRustTypeBinding(returnTypeBinding('dyn Trait + Send'))?.rawTypeName).toBe(
+      'Trait',
+    );
+  });
+
+  it('leaves ordinary (non-dyn) type names untouched', () => {
+    expect(normalizeRustTypeName('Behaviour')).toBe('Behaviour');
+    expect(normalizeRustTypeName('&Behaviour')).toBe('Behaviour');
+    expect(normalizeRustTypeName('Box<Behaviour>')).toBe('Behaviour');
+  });
+});