Properly send custom message in a synchronous manner (#1888)

Author: cpsievert

CHANGELOG.md

@@ -15,6 +15,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * Fixed an issue where the `<main>` areas of `ui.page_sidebar()` and `ui.page_navbar()` (with a `sidebar`) were made to be a fillable containers even when `fillable=False`. (#1816)
 
+* Fixed an issue where the `.update_user_input()` method on `ui.Chat()` isn't working in shinylive.  (#1891)
+
 ## [1.3.0] - 2025-03-03
 
 ### New features

shiny/ui/_chat.py

@@ -1107,16 +1107,13 @@ def update_user_input(
             }
         )
 
-        _utils.run_coro_sync(
-            self._session.send_custom_message(
-                "shinyChatMessage",
-                {
-                    "id": self.id,
-                    "handler": "shiny-chat-update-user-input",
-                    "obj": obj,
-                },
-            )
-        )
+        msg = {
+            "id": self.id,
+            "handler": "shiny-chat-update-user-input",
+            "obj": obj,
+        }
+
+        self._session._send_message_sync({"custom": {"shinyChatMessage": msg}})
 
     def set_user_message(self, value: str):
         """