fix: support AnnotatableBlock in the new content runtime (#268)

While extracting the Annotatable block from openedx-platform, we parted
ways with RawMixin, which contains the parse_xml_new_runtime method. That
method is still required by the extracted annotatable block to make it
compatible with the new content runtime, and it was missed during
extraction. So this change copies the method from RawMixin into the
extracted AnnotatableBlock.

Without this, loading an annotatable block in a Content Library crashed
with "XML Serialization is only supported with OpenedXContentRuntime",
because the base XBlock.parse_xml treats annotatable's nested OLX
(<instructions>, <p>, <annotation>) as child blocks and calls
runtime.add_node_as_child(), which the new runtime does not implement.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: farhan

xblocks_contrib/annotatable/annotatable.py

@@ -246,6 +246,28 @@ def workbench_scenarios():
             ),
         ]
 
+    @classmethod
+    def parse_xml_new_runtime(cls, node, runtime, keys):
+        """
+        Interpret the parsed XML in `node`, creating a new instance of this
+        module.
+        """
+        # In the new/openedx_content-based runtime, XModule parsing (from
+        # XmlMixin) is disabled, so definition_from_xml will not be
+        # called, and instead the "normal" XBlock parse_xml will be used.
+        # However, it's not compatible with RawMixin, so we implement
+        # support here.
+        data_field_value = cls.definition_from_xml(node, None)[0]["data"]
+        for child in node.getchildren():
+            node.remove(child)
+        # Get attributes, if any, via normal parse_xml.
+        try:
+            block = super().parse_xml_new_runtime(node, runtime, keys)
+        except AttributeError:
+            block = super().parse_xml(node, runtime, keys)
+        block.data = data_field_value
+        return block
+
     @classmethod
     def definition_from_xml(cls, xml_object, system):
         if len(xml_object) == 0 and len(list(xml_object.items())) == 0: