fix: Restore f-string placeholder for safety decision error message

Author: breeznik

agent.py

@@ -422,7 +422,7 @@ def _get_safety_confirmation(
         self, safety: dict[str, Any]
     ) -> Literal["CONTINUE", "TERMINATE"]:
         if safety["decision"] != "require_confirmation":
-            raise ValueError("Unknown safety decision: safety['decision']")
+            raise ValueError(f"Unknown safety decision: {safety['decision']}")
         termcolor.cprint(
             "Safety service requires explicit confirmation!",
             color="yellow",