add changeset

.changeset/nervous-goats-rescue.md

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+---
+"anywidget": patch
+"@anywidget/types": patch
+---
+
+Add experimental reducer API for sending/await-ing custom messages
+
+Introduces a unified API for dispatching messages from the front end, and
+await-ing response from Python. This removes a lot of boilerplate required for
+this kind of pattern previously. This API is experimental and opt-in, only if
+`_experimental_anywidget_reducer` is implemented on the anywidget subclass.
+
+```py
+class Widget(anywidget.AnyWidget):
+    _esm = """
+    async function render({ model, el, experimental }) {
+      let [response, buffers] = await experimental.dispatch("ping");
+      // Handle the response
+      console.log(response) // pong
+    }
+    export default { render };
+    """
+
+    def _experimental_anywidget_reducer(self, action, buffers):
+        assert action == "ping"
+        return "pong", []
+```