diff --git a/src/cleveragents/infrastructure/sandbox/strategy_registry.py b/src/cleveragents/infrastructure/sandbox/strategy_registry.py
index 04c8c68d..5d7335f7 100644
--- a/src/cleveragents/infrastructure/sandbox/strategy_registry.py
+++ b/src/cleveragents/infrastructure/sandbox/strategy_registry.py
@@ -259,14 +259,14 @@ class SandboxStrategyRegistry:
     # ------------------------------------------------------------------
 
     @staticmethod
-    def _validate_protocol(cls: type[Any]) -> None:
+    def _validate_protocol(klass: type[Any]) -> None:
         """Validate that a class satisfies :class:`SandboxStrategyProtocol`.
 
         Uses structural subtyping: checks that all 9 required methods
         are present as callable attributes on the class.
 
         Args:
-            cls: The class to validate.
+            klass: The class to validate.
 
         Raises:
             ProtocolMismatchError: If the class is missing required methods.
@@ -286,12 +286,12 @@ class SandboxStrategyRegistry:
         missing = [
             method
             for method in required_methods
-            if not callable(getattr(cls, method, None))
+            if not callable(getattr(klass, method, None))
         ]
 
         if missing:
             msg = (
-                f"Class '{cls.__name__}' does not satisfy "
+                f"Class '{klass.__name__}' does not satisfy "
                 f"SandboxStrategyProtocol. Missing methods: "
                 f"{', '.join(missing)}"
             )