Add proper error classification to distinguish expected states (item not
found) from critical failures (access denied, storage full) and
recoverable errors (device locked, auth failed).
Changes:
- Add KeychainReadResult and KeychainSaveResult enums with error types
- Add getIdentityKeyWithResult/saveIdentityKeyWithResult protocol methods
- Implement retry logic with exponential backoff for transient errors
- Add consistent SecureLogger logging for all keychain operations
- Update NoiseEncryptionService identity loading to handle errors gracefully
- Update MockKeychain and TrackingMockKeychain with error simulation
- Add comprehensive KeychainErrorHandlingTests (18 new tests)
Security: Applications can now properly detect and respond to critical
keychain failures, improving resilience during device lock states and
providing actionable diagnostics for access issues.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
