Add Direct Reply-To to 4.2.0 release notes

Release notes for #14474

Author: ansd

release-notes/4.2.0.md

@@ -17,6 +17,11 @@ AMQP 1.0 apps or client libraries must set the `durable` field of the header sec
 Team RabbitMQ recommends client libraries to send messages as durable by default.
 All AMQP 1.0 client libraries [maintained by Team RabbitMQ](https://www.rabbitmq.com/client-libraries/amqp-client-libraries) send messages as durable by default.
 
+### `Mandatory` flag in Direct Reply-To
+
+Starting with RabbitMQ 4.2, if an AMQP 0.9.1 Direct Reply-To responder (RPC server) publishes with the `mandatory` flag set, then `amq.rabbitmq.reply-to.*` is treated as a queue.
+Whether the requester (RPC client) is still there to consume the reply is not checked at routing time.
+In other words, if the responder publishes to only this queue name, then the message will be considered "routed" and RabbitMQ will therefore not send a `basic.return`.
 
 ## Release Highlights
 
@@ -55,6 +60,15 @@ To learn more, check out the new documentation guide on [Stream Filtering](https
 
 Pull Request: [#14184](https://github.com/rabbitmq/rabbitmq-server/pull/14184)
 
+### Direct Reply-To for AMQP 1.0
+
+RabbitMQ 4.2 adds Direct Reply-To support for AMQP 1.0, alongside the existing AMQP 0.9.1 implementation.
+It also works across protocols (e.g., AMQP 1.0 requester with AMQP 0.9.1 responder, or vice versa).
+
+For more information, read our updated documentation on [Direct Reply-To](https://www.rabbitmq.com/docs/next/direct-reply-to).
+
+Pull Request: [#14474](https://github.com/rabbitmq/rabbitmq-server/pull/14474)
+
 ### New Tooling for More Automated Blue-Green Deployment Migrations from 3.13.x Clusters to 4.2.x
 
 [Blue-Green Deployment migration from RabbitMQ 3.13.x](https://www.rabbitmq.com/blog/2025/07/29/latest-benefits-of-rmq-and-migrating-to-qq-along-the-way)
@@ -183,7 +197,7 @@ This section is **incomplete** and will be expanded as 4.2 approaches its releas
    can create:
 
    ```ini
-   # Applications won't be able to decalre more than 200 exchanges
+   # Applications won't be able to declare more than 200 exchanges
    # (including the protocol-standard pre-declared ones) in the cluster
    cluster_exchange_limit = 200
    ```