PR-003A: PostgreSQL Repository Adapters + Persistence Independence Test

- 4 PostgreSQL adapter stubs (Session, Mission, DecisionCase, Artifact)
- Migration 001: Initial schema (sessions, missions, artifacts, decision_cases)
- Persistence Independence Test: 6 tests verifying same behavior
  across InMemory and PostgreSQL implementations
- ADR-008: PostgreSQL Adapters for Production
- ADR-009: Persistence Independence

Architecture Quality Gates:
- Domain unchanged
- Application unchanged
- Only adapter implementation changes
- Same test suite runs against both implementations

Next: PR-003B — Schema & Migrations, PR-003C — Integration Tests,
PR-003D — Unit of Work / Transactions

packages/infrastructure/adr/ADR-008-PostgreSQL-Adapters.md

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+# ADR-008: PostgreSQL Adapters for Production
+
+## Status
+Accepted
+
+## Context
+In-memory adapters are sufficient for testing but not for production. We need persistent storage.
+
+## Decision
+Implement PostgreSQL adapters that implement the same repository interfaces as in-memory adapters:
+
+- PostgresFieldSessionRepository
+- PostgresMissionRepository
+- PostgresDecisionCaseRepository
+- PostgresArtifactRegistry
+
+Key principles:
+- Same interface as in-memory adapters
+- Domain unchanged
+- Application unchanged
+- Only adapter implementation changes
+
+## Consequences
+
+### Positive
+- Production-ready persistence
+- Same test suite verifies both implementations
+- Easy to swap implementations
+
+### Negative
+- Requires PostgreSQL instance
+- Need migrations
+- More complex setup
+
+## Related
+- ADR-006: In-Memory Adapters for Testing
+- ADR-009: Persistence Independence

packages/infrastructure/adr/ADR-009-Persistence-Independence.md

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+# ADR-009: Persistence Independence
+
+## Status
+Accepted
+
+## Context
+We need to ensure that business logic is not coupled to persistence implementation.
+
+## Decision
+Same use cases must produce same results regardless of repository implementation.
+
+### Verification Method
+1. Run test with InMemoryRepository
+2. Run test with PostgresRepository (when implemented)
+3. Compare results
+4. If different, adapter is wrong
+
+### Architecture Rules
+- Domain: 0 external dependencies
+- Application: only domain + contracts
+- Infrastructure: may depend on external libraries, never reverse
+- Persistence Independence: same use cases, same results
+
+## Consequences
+
+### Positive
+- Strong architecture verification
+- Easy to swap implementations
+- Tests document expected behavior
+
+### Negative
+- Need to maintain two test suites
+- PostgreSQL tests require database setup
+
+## Related
+- ADR-006: In-Memory Adapters for Testing
+- ADR-008: PostgreSQL Adapters for Production