diff --git a/openhcs/mcp/server.py b/openhcs/mcp/server.py
index 90a44d50e..d9978ca56 100644
--- a/openhcs/mcp/server.py
+++ b/openhcs/mcp/server.py
@@ -1986,9 +1986,8 @@ def control_args(
         arguments: Mapping[str, JsonValue],
         timeout_policy: type[McpControlTimeoutPolicy] = McpViewerTimeoutPolicy,
     ) -> "McpViewerConnectionToolArgs":
-        return dataclass_from_mapping(
-            McpViewerConnectionToolFields,
-            arguments,
+        return McpViewerConnectionToolFields.from_tool_arguments(
+            arguments
         ).to_control_args(timeout_policy)
 
     @staticmethod
@@ -2647,6 +2646,26 @@ class McpViewerConnectionToolFields:
     transport_mode: TransportMode | None = None
     timeout_ms: int | None = None
 
+    @classmethod
+    def from_tool_arguments(
+        cls,
+        arguments: Mapping[str, JsonValue],
+    ) -> Self:
+        """Reconstruct this record from its own declared tool fields."""
+        declared_names = tuple(
+            declared_field.name
+            for declared_field in dataclass_fields(cls)
+            if declared_field.init
+        )
+        return dataclass_from_mapping(
+            cls,
+            {
+                field_name: arguments[field_name]
+                for field_name in declared_names
+                if field_name in arguments
+            },
+        )
+
     @classmethod
     def signature_parameters(
         cls,
diff --git a/tests/unit/agent/test_mcp_server.py b/tests/unit/agent/test_mcp_server.py
index e2a984e10..41c0026f2 100644
--- a/tests/unit/agent/test_mcp_server.py
+++ b/tests/unit/agent/test_mcp_server.py
@@ -14830,6 +14830,7 @@ def test_mcp_viewer_connection_tool_fields_parse_nominal_transport_from_wire():
             "host": "127.0.0.1",
             "transport_mode": "tcp",
             "timeout_ms": 2000,
+            "route_key": "image-layer",
         },
         server.McpViewerCommandTimeoutPolicy,
     )