# Non-Functional Delta: 006 Messaging NATS Replacement

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

Parent state: `005-postgres-database-replacement`

## Runtime / Operations

*   Messaging broker is a standalone NATS container (single binary, low operational overhead).
*   Compose runtime adds NATS service and health gate before dependent service startup.
*   Ingress supports NATS websocket upgrade path for browser clients.

## Security / Compliance

*   Subject namespace design must avoid exposing internal-only subjects to browser subscriptions.
*   Browser-visible subjects are limited to account-scoped streams via documented naming policy.
*   No auth hardening changes are introduced in this state; auth/TLS hardening remains future non-functional states.

## Performance / Scalability

*   Broker should support higher fan-out and lower overhead than Socket.IO trade-feed role.
*   Subject-based routing with wildcards reduces application-layer channel orchestration complexity.

## Reliability / Observability

*   Messaging topology supports request/reply and optional future JetStream durability without redesign.
*   Broker health endpoint and connectivity checks are included in smoke/conformance expectations.