feat: better UX during refusal (#5260)

<img width="568" height="169" alt="Screenshot 2025-10-16 at 18 28 05"
src="https://github.com/user-attachments/assets/f42e8d6d-b7de-4948-b291-a5fbb50b1312"
/>

codex-rs/core/src/tools/mod.rs

@@ -238,6 +238,7 @@ fn truncate_function_error(err: FunctionCallError) -> FunctionCallError {
         FunctionCallError::RespondToModel(msg) => {
             FunctionCallError::RespondToModel(format_exec_output(&msg))
         }
+        FunctionCallError::Denied(msg) => FunctionCallError::Denied(format_exec_output(&msg)),
         FunctionCallError::Fatal(msg) => FunctionCallError::Fatal(format_exec_output(&msg)),
         other => other,
     }