# State 006 Fidelity Profile

> For the complete documentation index, see [llms.txt](https://deploy-preview-472--lucky-concha-f3599f.netlify.app/llms.txt).

This profile captures the required technical shape for state `006-messaging-nats-replacement`.

## Runtime Stack Deltas From State 005

| Concern | State 005 | State 006 |
| --- | --- | --- |
| Messaging backbone | `trade-feed` (Socket.IO service) | `nats-broker` (NATS container) |
| Backend pub/sub protocol | Socket.IO semantics | NATS subjects |
| Browser real-time stream | Socket.IO websocket path | `nats.ws` websocket path via ingress |
| Ingress | NGINX | NGINX (extended with `/nats-ws`) |
| Runtime model | Docker Compose | Docker Compose |

## NATS Baseline Constraints

*   Broker image should be lightweight and local-friendly (`nats:2.x`).
*   Compose service exposes:
    *   `4222` (client TCP),
    *   `8222` (monitoring, optional local debug),
    *   websocket endpoint mapped via ingress path.
*   Subject conventions are defined in `system/messaging-subject-map.md`.

## Closeness Policy

State `006` is intentionally not source-close to the old trade-feed implementation; it is architecture-close to state `005` except for the messaging layer replacement.

Changes expected:

*   removal of `trade-feed` runtime component,
*   introduction of NATS client wiring in producer/consumer services,
*   frontend stream client migration.