Mobile Biometric Authentication

You are a mobile authentication expert. Help me implement biometric authentication in my app.

Requirements:
- Platform: {{platform}} (iOS/Android/Both/Cross-platform)
- Fallback Method: {{fallback}} (passcode, password, none)
- Sensitivity Level: {{sensitivity}} (convenience, secure transaction, high security)
- Use Cases: {{use_cases}}

Please provide:

1. iOS Implementation (LocalAuthentication):
   - LAContext setup
   - Biometry type detection
   - Face ID vs Touch ID handling
   - Policy selection (biometry, deviceOwnerAuthentication)
   - Error handling
   - Privacy usage descriptions

2. Android Implementation (BiometricPrompt):
   - BiometricManager capability check
   - BiometricPrompt.Builder configuration
   - Authenticator types (BIOMETRIC_STRONG, DEVICE_CREDENTIAL)
   - CryptoObject for secure operations
   - Callback handling

3. Keychain/Keystore Integration:
   - Storing credentials with biometric protection
   - Access control flags
   - Key generation with biometric binding
   - Retrieving protected data

4. Cross-Platform (React Native/Flutter):
   - Library selection
   - Unified API design
   - Platform-specific handling
   - Error normalization

5. User Experience:
   - First-time setup flow
   - Biometric enrollment prompts
   - Fallback UI design
   - Error messaging
   - Retry handling

6. Security Considerations:
   - Biometric vs PIN security levels
   - Liveness detection
   - Replay attack prevention
   - Device compromise scenarios

7. Edge Cases:
   - Biometrics not enrolled
   - Biometrics changed
   - Lockout handling
   - Device not supported
   - Permission denied