Update changelog

Author: cpsievert

CHANGELOG.md

@@ -13,7 +13,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * Added a new `.add_sass_layer_file()` method to `ui.Theme` that supports reading a Sass file with layer boundary comments, e.g. `/*-- scss:defaults --*/`. This format [is supported by Quarto](https://quarto.org/docs/output-formats/html-themes-more.html#bootstrap-bootswatch-layering) and makes it easier to store Sass rules and declarations that need to be woven into Shiny's Sass Bootstrap files. (#1790)
 
-* The `ui.Chat()` component's `.on_user_submit()` decorator method now passes the user input to the decorated function. This makes it a bit more obvious how to access the user input inside the decorated function. See the new templates (mentioned below) for examples. (#1801)
+* The `ui.Chat()` component gains the following:
+    * The `.on_user_submit()` decorator method now passes the user input to the decorated function. This makes it a bit easier to access the user input. See the new templates (mentioned below) for examples. (#1801)
+    * The `.append_message_stream()` method now returns the `reactive.extended_task` instance that it launches. Among other things, this allows you to access the final result of the stream when it completes. (#1846)
 
 * `shiny create` includes new and improved `ui.Chat()` template options. Most of these templates leverage the new [`{chatlas}` package](https://posit-dev.github.io/chatlas/), our opinionated approach to interfacing with various LLM. (#1806)