Add render export adapter contract

src/markitect_tool/extension/builtins.py

@@ -5,6 +5,10 @@ from __future__ import annotations
 from markitect_tool.extension.registry import ExtensionDescriptor, ExtensionRegistry
 from markitect_tool.extension.processing import ProcessingCapability
 from markitect_tool.query import default_query_engine_registry
+from markitect_tool.render import (
+    default_render_export_adapter_registry,
+    render_export_registry_descriptor,
+)
 from markitect_tool.source import (
     default_source_adapter_registry,
     source_adapter_registry_descriptor,
@@ -28,9 +32,12 @@ def builtin_extension_registry() -> ExtensionRegistry:
         _memory_graph_contract_descriptor(),
         _memory_runtime_adapter_descriptor(),
         _agent_memory_descriptor(),
+        render_export_registry_descriptor(),
         source_adapter_registry_descriptor(),
     ]:
         registry.register(descriptor)
+    for descriptor in default_render_export_adapter_registry().extension_descriptors():
+        registry.register(descriptor)
     for descriptor in default_source_adapter_registry().extension_descriptors():
         registry.register(descriptor)
     return registry