Migrate PayGuard from Oracle to PostgreSQL and integrate HashiCorp Vault #26

Type: Infrastructure / Security / Database Migration
Priority: High
Component: Platform Infrastructure
Status: Planned

Objective

Modernize PayGuard's persistence and secrets-management infrastructure by migrating all applicable business services from Oracle to PostgreSQL and integrating self-hosted HashiCorp Vault.

Preserve PayGuard's financial correctness, customer identities, domain invariants, database ownership, and service isolation.

All implementation work is organized into six GitHub Sub-issues.

Sub-issues

1. Repository Inventory & Architecture Decisions
2. Oracle to PostgreSQL Migration
3. Concurrency & Transactional Correctness
4. HashiCorp Vault Integration
5. Integration & Security Testing
6. Documentation & Operational Handover

Track progress through GitHub's native Sub-issues feature. Each phase must be managed and reviewed independently.

Architectural Constraints

• Preserve one owned database per business service.
• Maintain customer identities and financial data integrity.
• Keep persistence and secrets infrastructure outside Domain models.
• Preserve JSpecify nullness contracts.
• Use open-source-compatible PostgreSQL, jOOQ, and Vault capabilities.
• Prevent destructive migrations or unauthorized data loss.
• Never commit secrets or use Vault root tokens in application services.
• Require reproducible tests before making correctness or security claims.
• Avoid unrelated authentication redesigns or framework migrations.

Definition of Done

• All six Sub-issues are completed.
• All applicable services have migrated to PostgreSQL.
• Vault integration is functional and verified.
• Required concurrency and security tests pass.
• Architecture Decision Records are completed.
• Migration and operational documentation are complete.
• Changes are reviewed and merged.
• Outstanding limitations are documented.

Ownership: All implementation is performed by the repository maintainer. This issue authorizes no automated repository modification.