chore: apply AI review suggestions for getGitCommitMessage error handling

- Use ignoreReturnCode: true in getExecOutput call and check exitCode
  explicitly, incorporating stderr into the thrown error for better
  diagnostics (copilot suggestion)
- Add try/catch around getExecOutput call to wrap thrown errors with
  descriptive message (covers the throw-path for gemini/copilot suggestions)
- Add tests for error path where getExecOutput throws (gemini suggestion)
- Add tests for error path where getExecOutput returns non-zero exit code
  (copilot suggestion)

Author: amondnet

src/__tests__/index.test.ts

@@ -157,6 +157,41 @@ describe('gitHub Action Integration', () => {
       expect(core.error).toBeDefined()
     })
   })
+
+  describe('getGitCommitMessage error paths', () => {
+    it('surfaces a descriptive error when getExecOutput throws', async () => {
+      vi.mocked(exec.getExecOutput).mockRejectedValueOnce(
+        new Error('spawn git ENOENT'),
+      )
+
+      vi.resetModules()
+      await import('../index')
+
+      // Allow the async run() to settle
+      await new Promise(resolve => setTimeout(resolve, 0))
+
+      expect(vi.mocked(core.setFailed)).toHaveBeenCalledWith(
+        expect.stringContaining('Failed to retrieve git commit message'),
+      )
+    })
+
+    it('surfaces a descriptive error when getExecOutput returns non-zero exit code', async () => {
+      vi.mocked(exec.getExecOutput).mockResolvedValueOnce({
+        exitCode: 128,
+        stdout: '',
+        stderr: 'fatal: not a git repository',
+      })
+
+      vi.resetModules()
+      await import('../index')
+
+      await new Promise(resolve => setTimeout(resolve, 0))
+
+      expect(vi.mocked(core.setFailed)).toHaveBeenCalledWith(
+        expect.stringContaining('Failed to retrieve git commit message'),
+      )
+    })
+  })
 })
 
 describe('octokit API v6 compatibility', () => {

src/index.ts

@@ -10,9 +10,14 @@ import { aliasDomainsToDeployment, createVercelClient, vercelDeploy, vercelInspe
 const { context } = github
 
 async function getGitCommitMessage(): Promise<string> {
+  let result: Awaited<ReturnType<typeof exec.getExecOutput>>
+
   try {
-    const { stdout } = await exec.getExecOutput('git', ['log', '-1', '--pretty=format:%B'], { silent: true })
-    return stdout.trim()
+    result = await exec.getExecOutput(
+      'git',
+      ['log', '-1', '--pretty=format:%B'],
+      { silent: true, ignoreReturnCode: true },
+    )
   }
   catch (error) {
     const message = error instanceof Error ? error.message : String(error)
@@ -21,6 +26,18 @@ async function getGitCommitMessage(): Promise<string> {
       + 'Ensure this action runs in a git repository with at least one commit.',
     )
   }
+
+  if (result.exitCode !== 0) {
+    const detail = result.stderr.trim()
+      || `git exited with code ${result.exitCode}`
+
+    throw new Error(
+      `Failed to retrieve git commit message: ${detail}. `
+      + 'Ensure this action runs in a git repository with at least one commit.',
+    )
+  }
+
+  return result.stdout.trim()
 }
 
 function logContextDebug(): void {