Extension framework optimization

tests/test_extension_registry.py

@@ -54,6 +54,8 @@ def test_extension_registry_lists_by_kind_and_capability():
     assert [descriptor.id for descriptor in registry.require_capability("fts")] == [
         "backend.local-sqlite"
     ]
+    assert registry.require_capability("missing") == []
+    assert registry.list(kind="missing") == []
 
 
 def test_extension_registry_rejects_duplicate_ids():