fix(test): address @claude review findings for parallel staleness PR

- Add missing checkStalenessAsync mock to calltool-dispatch.test.ts
  (BLOCKER: caused 5 CI failures on every list_repos test path)
- Add async invalid-commit-hash test for symmetry with sync suite
- Document why promisified execFile omits stdio option

gitnexus/src/core/git-staleness.ts

@@ -54,6 +54,8 @@ export async function checkStalenessAsync(
   lastCommit: string,
 ): Promise<StalenessInfo> {
   try {
+    // Note: promisified execFile captures stdout/stderr by default (no stdio option needed,
+    // unlike the sync variant which requires explicit stdio: ['pipe','pipe','pipe']).
     const { stdout } = await execFileAsync('git', ['rev-list', '--count', `${lastCommit}..HEAD`], {
       cwd: repoPath,
       encoding: 'utf-8',

gitnexus/test/unit/calltool-dispatch.test.ts

@@ -48,6 +48,7 @@ vi.mock('../../src/storage/repo-manager.js', () => ({
 // tests don't shell out to git.
 vi.mock('../../src/core/git-staleness.js', () => ({
   checkStaleness: vi.fn().mockReturnValue({ isStale: false, commitsBehind: 0 }),
+  checkStalenessAsync: vi.fn().mockResolvedValue({ isStale: false, commitsBehind: 0 }),
   checkCwdMatch: vi.fn().mockResolvedValue({ match: 'none' }),
 }));
 

gitnexus/test/unit/staleness.test.ts

@@ -109,6 +109,12 @@ describe('checkStalenessAsync', () => {
     expect(result.commitsBehind).toBe(0);
   });
 
+  it('fails open with invalid commit hash', async () => {
+    const result = await checkStalenessAsync(process.cwd(), 'not-a-real-commit-hash');
+    expect(result.isStale).toBe(false);
+    expect(result.commitsBehind).toBe(0);
+  });
+
   it('parallel calls complete faster than sequential', async () => {
     let headCommit: string;
     try {