整理配置和代码入口，增加部分测试。

tests/unit/test_registry_unified_handler_lookup.py

@@ -0,0 +1,49 @@
+from __future__ import annotations
+
+from pydantic import BaseModel
+
+from sync_state_machine.common.registry import DomainRegistry
+
+
+class RegistryLookupSchema(BaseModel):
+    __test__ = False
+    id: str
+
+
+class RegistryLookupNode:
+    __test__ = False
+
+
+class RegistryLookupJsonlHandler:
+    __test__ = False
+
+
+class RegistryLookupApiHandler:
+    __test__ = False
+
+
+class RegistryLookupDbHandler:
+    __test__ = False
+
+
+def test_registry_supports_unified_handler_lookup() -> None:
+    node_type = "registry_lookup_demo"
+
+    if DomainRegistry.is_registered(node_type):
+        reg = DomainRegistry.get_registration(node_type)
+        reg.jsonl_handler_class = RegistryLookupJsonlHandler
+        reg.api_handler_class = RegistryLookupApiHandler
+        reg.db_handler_class = RegistryLookupDbHandler
+    else:
+        DomainRegistry.register(
+            node_type=node_type,
+            schema=RegistryLookupSchema,
+            node_class=RegistryLookupNode,
+            jsonl_handler_class=RegistryLookupJsonlHandler,
+            api_handler_class=RegistryLookupApiHandler,
+            db_handler_class=RegistryLookupDbHandler,
+        )
+
+    assert DomainRegistry.get_handler(node_type, "jsonl") is RegistryLookupJsonlHandler
+    assert DomainRegistry.get_handler(node_type, "api") is RegistryLookupApiHandler
+    assert DomainRegistry.get_handler(node_type, "db") is RegistryLookupDbHandler