Research: PostgreSQL Database Replacement

Objective

Define the transition from state 003 to 009 by replacing H2 with PostgreSQL while preserving behavior.

Inputs Reviewed

• spec.md
• plan.md
• tasks.md
• requirements/functional-delta.md
• requirements/nonfunctional-delta.md
• system/architecture.md
• system/runtime-topology.md

Key Decisions

1. Use PostgreSQL as the default SQL persistence engine for this branch.
2. Preserve application-level behaviors and API compatibility from predecessor state.
3. Keep migration reversible and clearly isolated as a state-specific delta.