fix: address rpc and mcp review followups

tests/wf_transport_rpc_http/test_structure.py

@@ -2,8 +2,11 @@ from __future__ import annotations
 
 import importlib
 import inspect
+import pkgutil
 
+import wf_transport_rpc_http.client as rpc_client_package
 from wf_transport_rpc_http.client import RpcWorkflowApiClient
+from wf_transport_rpc_http.client.base import RpcCaller, RpcClientTransport
 
 
 def test_rpc_transport_has_domain_method_modules() -> None:
@@ -26,3 +29,20 @@ def test_rpc_transport_client_stays_thin() -> None:
     line_count = len(inspect.getsource(RpcWorkflowApiClient).splitlines())
 
     assert line_count < 40
+
+
+def test_rpc_client_mixins_share_one_call_contract() -> None:
+    call_owners = {
+        RpcClientTransport._call,
+        RpcCaller._call,
+    }
+
+    for module_info in pkgutil.iter_modules(rpc_client_package.__path__):
+        if module_info.name in {"__init__", "base"}:
+            continue
+        module = importlib.import_module(f"wf_transport_rpc_http.client.{module_info.name}")
+        for _name, value in inspect.getmembers(module, inspect.isclass):
+            if value.__module__ == module.__name__:
+                assert "_call" not in value.__dict__
+
+    assert len(call_owners) == 2