Implementation Plan: 007 Messaging NATS Replacement

Scope

• Transition from 005-postgres-database-replacement to 006-messaging-nats-replacement.
• Replace messaging component and protocol while preserving baseline business behavior.
• Keep runtime model on Docker Compose + NGINX ingress (no Kubernetes dependency in this state).

Technical Approach

1. Define architecture deltas:
   • remove Socket.IO trade-feed messaging role,
   • introduce nats-broker,
   • define backend and frontend messaging paths.
2. Define event/subject mapping for baseline flows (new trade, account updates, position updates).
3. Define compose and ingress snippets for NATS TCP + WS exposure.
4. Define backend migration rules:
   • publish/subscribe client changes per service.
5. Define frontend migration rules:
   • switch from Socket.IO subscription model to nats.ws consumer model (or documented gateway fallback if needed).
6. Define conformance + smoke checks for messaging compatibility and runtime operability.

Deliverables

1. Requirements and contracts deltas under requirements/ and contracts/.
2. fidelity-profile.md for state-level technical profile updates.
3. Updated architecture, topology, and migration guidance documents under system/.
4. Component and conformance docs for NATS messaging behavior.
5. Generation hook and smoke-test stubs for follow-on implementation.

Exit Criteria

• Architecture and migration intent are fully specified and reviewable.
• Runtime wiring examples (compose + ingress) are explicit.
• A clear path exists to implement generation/runtime scripts for state 006.
• State is ready for implementation phase and subsequent publish to code/generated-state-006-messaging-nats-replacement.