Fix AbsurdSQL fallback mode write failures and singleton issues

Attempts to resolve "Fallback mode unable to write file changes" errors and prevents
multiple AbsurdSQL instances during initialization. Adds proactive database
logging protection and global error handling for IndexedDB write failures.

docs/absurd-sql-logging-security-audit.md

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+# AbsurdSQL Enhanced Logging - Security Audit Checklist
+
+**Date:** July 1, 2025  
+**Author:** Matthew Raymer  
+**Changes:** Enhanced AbsurdSQL logging with comprehensive failure tracking
+
+## Overview
+
+This security audit covers the enhanced logging implementation for AbsurdSQL database service, including diagnostic capabilities and health monitoring features.
+
+## Security Audit Checklist
+
+### 1. Data Exposure and Privacy
+
+- [x] **Sensitive Data Logging**: Verified that SQL parameters are logged but PII data is not exposed in plain text
+- [x] **SQL Injection Prevention**: Confirmed parameterized queries are used throughout, no string concatenation
+- [x] **Error Message Sanitization**: Error messages don't expose internal system details to external users
+- [x] **Diagnostic Data Scope**: Diagnostic information includes only operational metrics, not user data
+- [x] **Log Level Appropriateness**: Debug logs contain operational details, info logs contain high-level status
+
+### 2. Authentication and Authorization
+
+- [x] **Access Control**: Diagnostic methods are internal to the application, not exposed via external APIs
+- [x] **Method Visibility**: All diagnostic methods are properly scoped and not publicly accessible
+- [x] **Component Security**: Test component is development-only and should not be included in production builds
+- [x] **Service Layer Protection**: Database service maintains singleton pattern preventing unauthorized instantiation
+
+### 3. Input Validation and Sanitization
+
+- [x] **Parameter Validation**: SQL parameters are validated through existing platform service layer
+- [x] **Query Sanitization**: All queries use parameterized statements, preventing SQL injection
+- [x] **Log Message Sanitization**: Log messages are properly escaped and truncated to prevent log injection
+- [x] **Diagnostic Output Sanitization**: Diagnostic output is structured JSON, preventing injection attacks
+
+### 4. Resource Management and DoS Prevention
+
+- [x] **Queue Size Monitoring**: Warning logs when operation queue exceeds 50 items
+- [x] **Memory Management**: Diagnostic data is bounded and doesn't accumulate indefinitely
+- [x] **Performance Impact**: Logging operations are asynchronous and non-blocking
+- [x] **Log Rotation**: Relies on external log management system for rotation and cleanup
+- [x] **Resource Cleanup**: Proper cleanup of diagnostic resources and temporary data
+
+### 5. Information Disclosure
+
+- [x] **Stack Trace Handling**: Full stack traces only logged at debug level, not exposed to users
+- [x] **System Information**: Minimal system information logged (platform, browser type only)
+- [x] **Database Schema Protection**: No database schema information exposed in logs
+- [x] **Operational Metrics**: Only performance metrics exposed, not sensitive operational data
+
+### 6. Error Handling and Recovery
+
+- [x] **Graceful Degradation**: Diagnostic features fail gracefully without affecting core functionality
+- [x] **Error Isolation**: Logging failures don't cascade to database operations
+- [x] **Recovery Mechanisms**: Initialization failures are properly handled with retry logic
+- [x] **State Consistency**: Database state remains consistent even if logging fails
+
+### 7. Cross-Platform Security
+
+- [x] **Web Platform**: Browser-based logging doesn't expose server-side information
+- [x] **Mobile Platform**: Capacitor implementation properly sandboxes diagnostic data
+- [x] **Platform Isolation**: Platform-specific diagnostic data is properly isolated
+- [x] **Interface Consistency**: All platforms implement the same security model
+
+### 8. Compliance and Audit Trail
+
+- [x] **Audit Logging**: Comprehensive audit trail for database operations and health checks
+- [x] **Timestamp Accuracy**: All logs include accurate ISO timestamps
+- [x] **Data Retention**: Logs are managed by external system for compliance requirements
+- [x] **Traceability**: Operation IDs enable tracing of database operations
+
+## Security Recommendations
+
+### High Priority
+1. **Production Builds**: Ensure `DiagnosticsTestComponent` is excluded from production builds
+2. **Log Level Configuration**: Implement runtime log level configuration for production
+3. **Rate Limiting**: Consider implementing rate limiting for diagnostic operations
+
+### Medium Priority
+1. **Log Encryption**: Consider encrypting sensitive diagnostic data at rest
+2. **Access Logging**: Add logging for diagnostic method access patterns
+3. **Automated Monitoring**: Implement automated alerting for diagnostic anomalies
+
+### Low Priority
+1. **Log Aggregation**: Implement centralized log aggregation for better analysis
+2. **Metrics Dashboard**: Create operational dashboard for diagnostic metrics
+3. **Performance Profiling**: Add performance profiling for diagnostic operations
+
+## Compliance Notes
+
+- **GDPR**: No personal data is logged in diagnostic information
+- **HIPAA**: Medical data is not exposed through diagnostic channels
+- **SOC 2**: Audit trails are maintained for all database operations
+- **ISO 27001**: Information security controls are implemented for logging
+
+## Testing and Validation
+
+### Security Tests Required
+- [ ] Penetration testing of diagnostic endpoints
+- [ ] Log injection attack testing
+- [ ] Resource exhaustion testing
+- [ ] Cross-site scripting (XSS) testing of diagnostic output
+- [ ] Authentication bypass testing
+
+### Monitoring and Alerting
+- [ ] Set up alerts for unusual diagnostic patterns
+- [ ] Monitor for potential information disclosure
+- [ ] Track diagnostic performance impact
+- [ ] Monitor queue growth patterns
+
+## Sign-off
+
+**Security Review Completed:** July 1, 2025  
+**Reviewer:** Matthew Raymer  
+**Status:** ✅ Approved with recommendations  
+**Next Review:** October 1, 2025