Properly clean up tmp files

__tests__/main.test.ts

@@ -75,6 +75,19 @@ vi.mock('fs', () => ({
   writeFileSync: mockWriteFileSync,
 }))
 
+// Mocks for tmp module to control temporary file creation and cleanup
+const mockRemoveCallback = vi.fn()
+const mockFileSync = vi.fn().mockReturnValue({
+  name: '/secure/temp/dir/modelResponse-abc123.txt',
+  removeCallback: mockRemoveCallback,
+})
+const mockSetGracefulCleanup = vi.fn()
+
+vi.mock('tmp', () => ({
+  fileSync: mockFileSync,
+  setGracefulCleanup: mockSetGracefulCleanup,
+}))
+
 // Mock MCP and inference modules
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
 const mockConnectToGitHubMCP = vi.fn() as MockedFunction<any>
@@ -269,4 +282,43 @@ describe('main.ts', () => {
     expect(core.setFailed).toHaveBeenCalledWith(`File for prompt-file was not found: ${promptFile}`)
     expect(mockProcessExit).toHaveBeenCalledWith(1)
   })
+
+  it('creates secure temporary files with proper cleanup', async () => {
+    mockInputs({
+      prompt: 'Test prompt',
+      'system-prompt': 'You are a test assistant.',
+    })
+
+    await run()
+
+    expect(mockSetGracefulCleanup).toHaveBeenCalledOnce()
+
+    expect(mockFileSync).toHaveBeenCalledWith({
+      prefix: 'modelResponse-',
+      postfix: '.txt',
+    })
+
+    expect(core.setOutput).toHaveBeenNthCalledWith(2, 'response-file', '/secure/temp/dir/modelResponse-abc123.txt')
+    expect(mockWriteFileSync).toHaveBeenCalledWith('/secure/temp/dir/modelResponse-abc123.txt', 'Hello, user!', 'utf-8')
+    expect(mockRemoveCallback).toHaveBeenCalledOnce()
+
+    expect(mockProcessExit).toHaveBeenCalledWith(0)
+  })
+
+  it('handles cleanup errors gracefully', async () => {
+    mockRemoveCallback.mockImplementationOnce(() => {
+      throw new Error('Cleanup failed')
+    })
+
+    mockInputs({
+      prompt: 'Test prompt',
+      'system-prompt': 'You are a test assistant.',
+    })
+
+    await run()
+
+    expect(mockRemoveCallback).toHaveBeenCalledOnce()
+    expect(core.warning).toHaveBeenCalledWith('Failed to cleanup temporary file: Error: Cleanup failed')
+    expect(mockProcessExit).toHaveBeenCalledWith(0)
+  })
 })