- Implement comprehensive encryption key lifecycle management with secure storage, rotation, and retirement
- Add KeyManager<DB> with full PostgreSQL and MySQL support for enterprise-grade key operations
- Support for multiple encryption algorithms: AES-256-GCM and ChaCha20-Poly1305 with configurable key strengths
- Master key encryption (KEK) system ensuring data encryption keys are never stored in plaintext
- Automatic key rotation with configurable intervals and next rotation scheduling
- Key versioning system supporting up to configurable maximum versions per key ID
- Secure key derivation using Argon2 with customizable memory cost, time cost, and parallelism parameters

Database Schema and Migration Support:
- New hammerwork_encryption_keys table with comprehensive metadata tracking and optimized indexes
- New hammerwork_key_audit_log table for complete audit trail of all key operations
- Database migration files for both PostgreSQL (013_add_key_audit.postgres.sql) and MySQL (013_add_key_audit.mysql.sql)
- Proper constraint validation ensuring data integrity and encryption consistency
- Optimized indexes for key lookup, rotation queries, expiration tracking, and audit log searches

Advanced Key Operations:
- store_key() and load_key() operations with automatic encryption and version management
- retire_key_version() for secure key retirement while maintaining decryption capabilities
- cleanup_old_key_versions() with configurable retention policies preventing key sprawl
- get_keys_due_for_rotation() for automated rotation scheduling and compliance
- record_key_usage() with comprehensive usage statistics and last access tracking
- record_audit_event() providing complete audit trails for compliance and security monitoring

Security and Compliance Features:
- External Key Management Service (KMS) integration support for AWS KMS, Azure Key Vault, HashiCorp Vault
- Key source management supporting environment variables, static keys, generated keys, and external services
- Comprehensive audit logging with operation type, success/failure tracking, and error message capture
- Key purpose categorization: Encryption, MAC (Message Authentication Code), and KEK (Key Encryption Key)
- Key status management: Active, Retired, Revoked, and Expired with proper lifecycle transitions
- Configurable key expiration, rotation intervals, and automated cleanup policies

Key Management Statistics and Monitoring:
- KeyManagerStats providing comprehensive metrics: total keys, active/retired/revoked/expired counts
- Key usage analytics: total access operations, rotations performed, average key age
- Proactive monitoring: keys expiring soon alerts and rotation due notifications
- Performance metrics and key management health indicators

Configuration and Flexibility:
- KeyManagerConfig with fluent builder pattern for easy configuration management
- Support for auto-rotation with configurable intervals and maximum key version limits
- Audit logging enable/disable with comprehensive event tracking
- External KMS configuration with service type, endpoint, authentication, and namespace support
- Key derivation configuration with Argon2 parameter tuning for security vs. performance optimization

Testing and Quality:
- Added 20 comprehensive unit tests covering all key management functionality
- Error handling tests validating robust parsing and graceful failure modes
- Database operation tests ensuring proper integration with both PostgreSQL and MySQL
- Configuration validation tests for all builder patterns and default values
- Serialization/deserialization tests ensuring cross-system compatibility

Code Quality and Maintainability:
- Exposed parsing helper functions (parse_algorithm, parse_key_source, parse_key_purpose, parse_key_status) for extensibility
- Implemented Display traits for all key management enums enabling human-readable output
- Added comprehensive error types and messages for debugging and troubleshooting
- Proper feature flag isolation ensuring encryption functionality is optional and self-contained

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>