test(embed): cover resolveNpmInstallCwd happy path

Mock createRequire so resolve returns a synthetic scoped package.json
path, then assert the 4 dirname hops land at the host directory.
Without this, only the catch-to-undefined branch was exercised and a
miscounted dirname would pass CI silently.

Closes follow-up suggestion from #1178 review.

Author: carlos-alm

src/domain/search/models.ts

@@ -19,8 +19,10 @@ const _require = createRequire(import.meta.url);
  *
  * Pin cwd to the directory that contains @optave/codegraph's `node_modules`
  * so the install lands where Node's resolution algorithm will find it.
+ *
+ * @internal Exported for unit tests; not part of the public barrel.
  */
-function resolveNpmInstallCwd(): string | undefined {
+export function resolveNpmInstallCwd(): string | undefined {
   try {
     const pkgJsonPath = _require.resolve('@optave/codegraph/package.json');
     // pkgJsonPath = <host>/node_modules/@optave/codegraph/package.json

tests/unit/prompt-install.test.ts

@@ -8,6 +8,7 @@
  * so every test gets a fresh embedder module with its own mocks.
  */
 
+import path from 'node:path';
 import { afterEach, beforeEach, describe, expect, test, vi } from 'vitest';
 
 const expectedNpmBin = process.platform === 'win32' ? 'npm.cmd' : 'npm';
@@ -186,3 +187,48 @@ describe('loadTransformers install prompt', () => {
     expect(exitSpy).not.toHaveBeenCalled();
   });
 });
+
+describe('resolveNpmInstallCwd', () => {
+  beforeEach(() => {
+    vi.resetModules();
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  test('returns host directory (4 dirname hops from scoped package.json)', async () => {
+    const fakePkg = path.join(
+      path.sep,
+      'host',
+      'node_modules',
+      '@optave',
+      'codegraph',
+      'package.json',
+    );
+    vi.doMock('node:module', () => ({
+      createRequire: () => ({
+        resolve: (req: string) => {
+          if (req === '@optave/codegraph/package.json') return fakePkg;
+          throw new Error(`Cannot find: ${req}`);
+        },
+      }),
+    }));
+
+    const { resolveNpmInstallCwd } = await import('../../src/domain/search/models.js');
+    expect(resolveNpmInstallCwd()).toBe(path.join(path.sep, 'host'));
+  });
+
+  test('returns undefined when @optave/codegraph cannot be resolved', async () => {
+    vi.doMock('node:module', () => ({
+      createRequire: () => ({
+        resolve: () => {
+          throw new Error('Cannot find module @optave/codegraph');
+        },
+      }),
+    }));
+
+    const { resolveNpmInstallCwd } = await import('../../src/domain/search/models.js');
+    expect(resolveNpmInstallCwd()).toBeUndefined();
+  });
+});