ENH: Give more helpful error message on serialization fail

Author: mferrera

src/runrms/api/proxy.py

@@ -154,6 +154,16 @@ def _send_request(self, request: Request) -> Response:
                     response.traceback,
                 )
             return response
+        except TypeError as e:
+            raise TypeError(
+                "Unable to serialize request to rmsapi. This can happen for "
+                "several reasons:\n"
+                "1. You're using an attribute like 'some.attr' directly. You must "
+                "instead use 'some.attr.get()' to use the actual value.\n"
+                "2. You're passing an object where some attribute is being used "
+                "in a way similar to 1. You must called '.get()' on it first.\n"
+                f"Details: Request: {request}, Error: {e}"
+            ) from e
         except zmq.Again as e:
             logger.error(f"Request timed out after {self._rcv_timeout_ms}ms")
             raise TimeoutError(f"Request timed out: {e}") from e

tests/test_api/test_proxy.py

@@ -531,3 +531,11 @@ def test_get_on_root_raises(proxy_with_mocks: RmsApiProxy) -> None:
     """get() on root proxy raises."""
     with pytest.raises(RuntimeError, match="Cannot get value of root proxy"):
         proxy_with_mocks.get()
+
+
+def test_no_get_on_dict_key_raises(proxy_with_mocks: RmsApiProxy) -> None:
+    """Helpful serialization error is raised when using an RmsApiProxy as an arg."""
+    some = {}
+
+    with pytest.raises(TypeError, match="Unable to serialize request to rmsapi"):
+        some[proxy_with_mocks.some_attr] = "foo"