# ADR-0005: In-memory default adapters

• Status: accepted
• Date: 2026-04-23

# Context

The reference implementation must boot and pass the full test suite on a fresh clone, without Docker, Postgres, or Valkey. Yet it must also be a credible starting point for a production deployment.

# Decision

Ship in-memory repositories, event bus, and delivery journal as the default adapters. They implement the same application/ports.ts interfaces as any future Postgres / Valkey backing. Production adapters plug in via composition-root.ts without touching application code.

# Consequences

• Zero-setup onboarding for contributors.
• The tests that matter (domain rules, use cases, HTTP endpoints) run end-to-end with no external services.
• Adapters are designed to be swappable: the in-memory implementation is not a stub but a real implementation of the port contract.
• Risk: someone may deploy the in-memory version to production. We mitigate with clear docs (SETUP.md) and explicit "production" adapters in infra/helm/.

# Alternatives considered

• Testcontainers: requires Docker even for unit tests. Rejected.
• SQLite as default: simpler than Postgres but still adds initialisation complexity; rejected in favour of a pure in-memory default.