diff --git a/src/App.tsx b/src/App.tsx
index 9b0dbd5..ead6205 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -239,10 +239,6 @@ function App() {
           }
         });
 
-        // Auto-select first file if none selected
-        if (!selectedFileId) {
-          setSelectedFileId(fileRecords[0].id);
-        }
       } else {
         setFiles([]);
       }
@@ -569,18 +565,6 @@ function App() {
           </div>
         )}
       </div>
-
-      {/* ICP Footer */}
-      <div className="flex-shrink-0 bg-white border-t border-gray-200 py-2 px-4 text-center">
-        <a
-          href="https://beian.miit.gov.cn"
-          target="_blank"
-          rel="noopener noreferrer"
-          className="text-xs text-gray-500 hover:text-gray-700 transition-colors"
-        >
-          京ICP备2025152973号
-        </a>
-      </div>
     </div>
   );
 }
diff --git a/src/components/AuthModal.tsx b/src/components/AuthModal.tsx
index 590f5d7..04e04d6 100644
--- a/src/components/AuthModal.tsx
+++ b/src/components/AuthModal.tsx
@@ -17,6 +17,7 @@ export default function AuthModal({ onClose, mandatory = false }: AuthModalProps
   const [password, setPassword] = useState('');
   const [confirmPassword, setConfirmPassword] = useState('');
   const [localError, setLocalError] = useState('');
+  const [fieldErrors, setFieldErrors] = useState<{ email?: string; password?: string; confirmPassword?: string }>({});
 
   const isBusy = useMemo(
     () => ['email_signing_in', 'email_signing_up', 'oauth_redirecting', 'oauth_exchanging'].includes(authPhase),
@@ -28,20 +29,37 @@ export default function AuthModal({ onClose, mandatory = false }: AuthModalProps
   const handleSubmit = async (e: React.FormEvent) => {
     e.preventDefault();
     setLocalError('');
+    const nextFieldErrors: { email?: string; password?: string; confirmPassword?: string } = {};
+    const normalizedEmail = email.trim();
+
+    if (!normalizedEmail) {
+      nextFieldErrors.email = t.auth.emailRequired;
+    } else if (!/^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(normalizedEmail)) {
+      nextFieldErrors.email = t.auth.emailInvalid;
+    }
+
+    if (!password) {
+      nextFieldErrors.password = t.auth.passwordRequired;
+    }
 
     if (mode === 'signup') {
-      if (password.length < 6) {
-        setLocalError(t.auth.passwordHint);
-        return;
+      if (password && password.length < 6) {
+        nextFieldErrors.password = t.auth.passwordHint;
       }
 
-      if (password !== confirmPassword) {
-        setLocalError(t.auth.passwordMismatch);
-        return;
+      if (!confirmPassword) {
+        nextFieldErrors.confirmPassword = t.auth.passwordRequired;
+      } else if (password !== confirmPassword) {
+        nextFieldErrors.confirmPassword = t.auth.passwordMismatch;
       }
     }
 
-    const result = mode === 'signup' ? await signUp(email, password) : await signIn(email, password);
+    setFieldErrors(nextFieldErrors);
+    if (Object.keys(nextFieldErrors).length > 0) {
+      return;
+    }
+
+    const result = mode === 'signup' ? await signUp(normalizedEmail, password) : await signIn(normalizedEmail, password);
 
     if (!result.error) {
       onClose();
@@ -75,7 +93,11 @@ export default function AuthModal({ onClose, mandatory = false }: AuthModalProps
         <div className="grid grid-cols-2 gap-2 rounded-lg bg-gray-100 p-1 mb-4">
           <button
             type="button"
-            onClick={() => setMode('signin')}
+            onClick={() => {
+              setMode('signin');
+              setFieldErrors({});
+              setLocalError('');
+            }}
             aria-pressed={mode === 'signin'}
             disabled={isBusy}
             className={`rounded-md px-3 py-2 text-sm font-medium transition-colors ${
@@ -86,7 +108,11 @@ export default function AuthModal({ onClose, mandatory = false }: AuthModalProps
           </button>
           <button
             type="button"
-            onClick={() => setMode('signup')}
+            onClick={() => {
+              setMode('signup');
+              setFieldErrors({});
+              setLocalError('');
+            }}
             aria-pressed={mode === 'signup'}
             disabled={isBusy}
             className={`rounded-md px-3 py-2 text-sm font-medium transition-colors ${
@@ -97,7 +123,7 @@ export default function AuthModal({ onClose, mandatory = false }: AuthModalProps
           </button>
         </div>
 
-        <form onSubmit={handleSubmit} className="space-y-4">
+        <form onSubmit={handleSubmit} noValidate className="space-y-4">
           <div>
             <label htmlFor="auth-email" className="block text-sm font-medium text-gray-700 mb-1">
               {t.auth.email}
@@ -106,12 +132,20 @@ export default function AuthModal({ onClose, mandatory = false }: AuthModalProps
               id="auth-email"
               type="email"
               value={email}
-              onChange={(e) => setEmail(e.target.value)}
-              className="w-full px-4 py-2 border border-gray-300 rounded-lg focus:ring-2 focus:ring-blue-500 focus:border-transparent"
+              onChange={(e) => {
+                setEmail(e.target.value);
+                if (fieldErrors.email) {
+                  setFieldErrors((prev) => ({ ...prev, email: undefined }));
+                }
+              }}
+              className={`w-full px-4 py-2 border rounded-lg focus:ring-2 focus:ring-blue-500 focus:border-transparent ${
+                fieldErrors.email ? 'border-red-400' : 'border-gray-300'
+              }`}
               placeholder="your@email.com"
               required
               disabled={isBusy}
             />
+            {fieldErrors.email && <p className="mt-1 text-xs text-red-600">{fieldErrors.email}</p>}
             {mode === 'signup' && (
               <p className="mt-1 text-xs text-gray-500">{t.auth.emailHint}</p>
             )}
@@ -125,13 +159,21 @@ export default function AuthModal({ onClose, mandatory = false }: AuthModalProps
               id="auth-password"
               type="password"
               value={password}
-              onChange={(e) => setPassword(e.target.value)}
-              className="w-full px-4 py-2 border border-gray-300 rounded-lg focus:ring-2 focus:ring-blue-500 focus:border-transparent"
+              onChange={(e) => {
+                setPassword(e.target.value);
+                if (fieldErrors.password) {
+                  setFieldErrors((prev) => ({ ...prev, password: undefined }));
+                }
+              }}
+              className={`w-full px-4 py-2 border rounded-lg focus:ring-2 focus:ring-blue-500 focus:border-transparent ${
+                fieldErrors.password ? 'border-red-400' : 'border-gray-300'
+              }`}
               placeholder="••••••••"
               required
               minLength={6}
               disabled={isBusy}
             />
+            {fieldErrors.password && <p className="mt-1 text-xs text-red-600">{fieldErrors.password}</p>}
             {mode === 'signup' && (
               <p className="mt-1 text-xs text-gray-500">{t.auth.passwordHint}</p>
             )}
@@ -146,13 +188,21 @@ export default function AuthModal({ onClose, mandatory = false }: AuthModalProps
                 id="auth-password-confirm"
                 type="password"
                 value={confirmPassword}
-                onChange={(e) => setConfirmPassword(e.target.value)}
-                className="w-full px-4 py-2 border border-gray-300 rounded-lg focus:ring-2 focus:ring-blue-500 focus:border-transparent"
+                onChange={(e) => {
+                  setConfirmPassword(e.target.value);
+                  if (fieldErrors.confirmPassword) {
+                    setFieldErrors((prev) => ({ ...prev, confirmPassword: undefined }));
+                  }
+                }}
+                className={`w-full px-4 py-2 border rounded-lg focus:ring-2 focus:ring-blue-500 focus:border-transparent ${
+                  fieldErrors.confirmPassword ? 'border-red-400' : 'border-gray-300'
+                }`}
                 placeholder="••••••••"
                 required
                 minLength={6}
                 disabled={isBusy}
               />
+              {fieldErrors.confirmPassword && <p className="mt-1 text-xs text-red-600">{fieldErrors.confirmPassword}</p>}
             </div>
           )}
 
diff --git a/src/components/__tests__/App.test.tsx b/src/components/__tests__/App.test.tsx
index 39fb1cc..0c1c7ee 100644
--- a/src/components/__tests__/App.test.tsx
+++ b/src/components/__tests__/App.test.tsx
@@ -1,7 +1,8 @@
-import { fireEvent, render, screen } from '@testing-library/react';
+import { fireEvent, render, screen, waitFor } from '@testing-library/react';
 import { beforeEach, describe, expect, it, vi } from 'vitest';
 
 import App from '../../App';
+import { uploadService } from '../../lib/uploadService';
 
 const { useAuthMock } = vi.hoisted(() => ({
   useAuthMock: vi.fn(),
@@ -57,7 +58,7 @@ vi.mock('../../components/LeftSidebar', () => ({
 }));
 
 vi.mock('../../components/FilePreview', () => ({
-  default: () => <div>preview</div>,
+  default: ({ file }: { file: { id: string } | null }) => <div>{file ? `preview:${file.id}` : 'preview-empty'}</div>,
 }));
 
 vi.mock('../../components/ResultPanel', () => ({
@@ -110,3 +111,48 @@ describe('App anonymous usage limit', () => {
     expect(screen.queryByText('upload-modal')).not.toBeInTheDocument();
   });
 });
+
+describe('App initial selection', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    localStorage.clear();
+    localStorage.setItem('hasSeenGuide', 'true');
+  });
+
+  it('does not auto-select the first history record on initial load', async () => {
+    useAuthMock.mockReturnValue({
+      user: { id: 'u1' },
+      initializing: false,
+    });
+
+    vi.mocked(uploadService.getTaskList).mockResolvedValue({
+      total: 1,
+      task_list: [
+        {
+          task_id: 'task-1',
+          file_name: 'sample.png',
+          status: 2,
+          origin_url: 'https://example.com/sample.png',
+          task_type: 'FORMULA',
+          created_at: '2026-03-06T00:00:00Z',
+          latex: '',
+          markdown: 'content',
+          mathml: '',
+          mml: '',
+          image_blob: '',
+          docx_url: '',
+          pdf_url: '',
+        },
+      ],
+    });
+
+    render(<App />);
+
+    await waitFor(() => {
+      expect(uploadService.getTaskList).toHaveBeenCalled();
+    });
+
+    expect(screen.getByText('preview-empty')).toBeInTheDocument();
+    expect(screen.queryByText('preview:task-1')).not.toBeInTheDocument();
+  });
+});
diff --git a/src/components/__tests__/AuthModal.test.tsx b/src/components/__tests__/AuthModal.test.tsx
index c973246..944db69 100644
--- a/src/components/__tests__/AuthModal.test.tsx
+++ b/src/components/__tests__/AuthModal.test.tsx
@@ -4,6 +4,9 @@ import { describe, expect, it, vi } from 'vitest';
 import AuthModal from '../AuthModal';
 
 const useAuthMock = vi.fn();
+const signInMock = vi.fn().mockResolvedValue({ error: null });
+const signUpMock = vi.fn().mockResolvedValue({ error: null });
+const beginGoogleOAuthMock = vi.fn().mockResolvedValue({ error: null });
 
 vi.mock('../../contexts/AuthContext', () => ({
   useAuth: () => useAuthMock(),
@@ -28,21 +31,37 @@ vi.mock('../../contexts/LanguageContext', () => ({
         passwordHint: '密码至少 6 位，建议使用字母和数字组合。',
         confirmPassword: '确认密码',
         passwordMismatch: '两次输入的密码不一致。',
+        emailRequired: '请输入邮箱地址。',
+        emailInvalid: '请输入有效的邮箱地址。',
+        passwordRequired: '请输入密码。',
         oauthRedirecting: '正在跳转 Google...',
       },
     },
   }),
 }));
 
+const createAuthState = (overrides?: Record<string, unknown>) => ({
+  signIn: signInMock,
+  signUp: signUpMock,
+  beginGoogleOAuth: beginGoogleOAuthMock,
+  authPhase: 'idle',
+  authError: null,
+  ...overrides,
+});
+
 describe('AuthModal', () => {
+  it('shows email required message for empty signin submit', async () => {
+    useAuthMock.mockReturnValue(createAuthState());
+    render(<AuthModal onClose={vi.fn()} />);
+
+    fireEvent.click(document.querySelector('button[type="submit"]') as HTMLButtonElement);
+
+    expect(await screen.findByText('请输入邮箱地址。')).toBeInTheDocument();
+    expect(signInMock).not.toHaveBeenCalled();
+  });
+
   it('renders google oauth button', () => {
-    useAuthMock.mockReturnValue({
-      signIn: vi.fn().mockResolvedValue({ error: null }),
-      signUp: vi.fn().mockResolvedValue({ error: null }),
-      beginGoogleOAuth: vi.fn().mockResolvedValue({ error: null }),
-      authPhase: 'idle',
-      authError: null,
-    });
+    useAuthMock.mockReturnValue(createAuthState());
 
     render(<AuthModal onClose={vi.fn()} />);
 
@@ -50,13 +69,7 @@ describe('AuthModal', () => {
   });
 
   it('disables inputs and submit while oauth redirecting', () => {
-    useAuthMock.mockReturnValue({
-      signIn: vi.fn().mockResolvedValue({ error: null }),
-      signUp: vi.fn().mockResolvedValue({ error: null }),
-      beginGoogleOAuth: vi.fn().mockResolvedValue({ error: null }),
-      authPhase: 'oauth_redirecting',
-      authError: null,
-    });
+    useAuthMock.mockReturnValue(createAuthState({ authPhase: 'oauth_redirecting' }));
 
     render(<AuthModal onClose={vi.fn()} />);
 
@@ -68,13 +81,7 @@ describe('AuthModal', () => {
   });
 
   it('switches between signin and signup with segmented tabs', () => {
-    useAuthMock.mockReturnValue({
-      signIn: vi.fn().mockResolvedValue({ error: null }),
-      signUp: vi.fn().mockResolvedValue({ error: null }),
-      beginGoogleOAuth: vi.fn().mockResolvedValue({ error: null }),
-      authPhase: 'idle',
-      authError: null,
-    });
+    useAuthMock.mockReturnValue(createAuthState());
 
     render(<AuthModal onClose={vi.fn()} />);
 
@@ -85,13 +92,7 @@ describe('AuthModal', () => {
   });
 
   it('shows friendlier signup guidance', () => {
-    useAuthMock.mockReturnValue({
-      signIn: vi.fn().mockResolvedValue({ error: null }),
-      signUp: vi.fn().mockResolvedValue({ error: null }),
-      beginGoogleOAuth: vi.fn().mockResolvedValue({ error: null }),
-      authPhase: 'idle',
-      authError: null,
-    });
+    useAuthMock.mockReturnValue(createAuthState());
 
     render(<AuthModal onClose={vi.fn()} />);
 
diff --git a/src/lib/translations.ts b/src/lib/translations.ts
index c413c1d..a737362 100644
--- a/src/lib/translations.ts
+++ b/src/lib/translations.ts
@@ -62,6 +62,9 @@ export const translations = {
       noAccount: 'No account? Register',
       continueWithGoogle: 'Google',
       emailHint: 'Used only for sign-in and history sync.',
+      emailRequired: 'Please enter your email address.',
+      emailInvalid: 'Please enter a valid email address.',
+      passwordRequired: 'Please enter your password.',
       passwordHint: 'Use at least 6 characters. Letters and numbers are recommended.',
       confirmPassword: 'Confirm Password',
       passwordMismatch: 'The two passwords do not match.',
@@ -167,6 +170,9 @@ export const translations = {
       noAccount: '没有账号？去注册',
       continueWithGoogle: 'Google',
       emailHint: '仅用于登录和同步记录。',
+      emailRequired: '请输入邮箱地址。',
+      emailInvalid: '请输入有效的邮箱地址。',
+      passwordRequired: '请输入密码。',
       passwordHint: '密码至少 6 位，建议使用字母和数字组合。',
       confirmPassword: '确认密码',
       passwordMismatch: '两次输入的密码不一致。',